Showing papers in "The Journal of Agricultural Science in 2007"

Conservation agriculture : what is it and why is it important for future sustainable food production?

Abstract: Conservation agriculture (CA), defined as minimal soil disturbance (no-till) and permanent soil cover (mulch) combined with rotations, is a more sustainable cultivation system for the future than those presently practised. The present paper first introduces the reasons for tillage in agriculture and discusses how this age-old agricultural practice is responsible for the degradation of natural resources and soils. The paper goes on to introduce conservation tillage (CT), a minimum tillage and surface mulch practice that was developed in response to the severe wind erosion caused by mouldboard tillage of grasslands and referred to as the American dust bowl of the 1930s. CT is then compared with CA, a suggested improvement on CT, where no-till, mulch, and rotations significantly improve soil properties (physical, biological, and chemical) and other biotic factors, enabling more efficient use of natural resources. CA can improve agriculture through improvement in water infiltration and reducing erosion, improving soil surface aggregates, reducing compaction through promotion of biological tillage, increasing surface soil organic matter and carbon content, moderating soil temperatures, and suppressing weeds. CA also helps reduce costs of production, saves time, increases yield through more timely planting, reduces diseases and pests through stimulation of biological diversity, and reduces greenhouse gas emissions. Availability of suitable equipment is a major constraint to successful CA, but advances in design and manufacture of seed drills by local manufacturers are enabling farmers to experiment and accept this technology in many parts of the world. Estimates of farmer adoption of CA are close to 100 million ha in 2005, indicating that farmers are convinced of the benefits of this technology. The paper concludes that agriculture in the next decade will have to produce more food, sustainably, from less land through more efficient use of natural resources and with minimal impact on the environment in order to meet growing population demands. This will be a significant challenge for agricultural scientists, extension personnel, and farmers. Promoting and adopting CA management systems can help meet this complex goal.

PAPER PRESENTED AT INTERNATIONAL WORKSHOP ON INCREASING WHEAT YIELD POTENTIAL, CIMMYT, OBREGON, MEXICO, 20–24 MARCH 2006 Understanding the physiological basis of yield potential in wheat

Abstract: The present paper focuses on the physiology of yield potential in wheat (Triticum aestivum L.), because breeding progress in yield potential has overtaken farm yield progress. The paper examines developments largely in the last 10 years seeking routes to higher yield potential. Lately this subject has come under pressure from two new imperatives: perceived slowing of genetic progress and ambitious functional genomics. Analysis of trials between 1996 and 2005 at the CIANO research centre in northwest Mexico suggests that yield potential progress in CIMMYT spring wheats has slowed to around 0·50% per year, but has not ceased there nor in winter wheats elsewhere. Meanwhile, in the last 10 years or so, physiological understanding has advanced somewhat. Increased kernel number/m2 remains strongly associated with genetic progress in grain yield, and new research reinforces the importance of spike dry weight (g/m2) at anthesis in its determination. Lengthening the spike growth period through manipulation of sensitivity to photoperiod looks promising, but more attention to kernels per unit of spike weight is also urged. With respect to plant height, an optimum somewhere between 0·7 and 1·0 m is accepted and we are moving away from infatuation with the Norin 10 dwarfing genes as a way of reaching that. What has not been achieved is good lodging resistance in all short spring wheats, nor a complete understanding of its physiological basis. New information is coming to light on the possible role of stored stem reserves at anthesis, for these reserves appear to have increased as yield potential has increased. Part of the benefit may be related to assimilate supply per kernel around anthesis, which new understanding suggests is important for maximum potential kernel weight. Nevertheless, results continue to suggest that despite more kernels/m2, the most recent wheats are still largely sink-limited during grain filling. Growing evidence from spring and winter wheat (and from rice and maize) now points to the importance of increased photosynthetic activity before and around flowering for recent genetic increases in yield potential. This opens up new possibilities for selection in field plots. Finally, attention is given to effects of weather on yield potential and recent advances in techniques for elucidating the physiological basis of genotype by year interactions. From physiological understanding such as described, traits can be suggested as possible selection criteria for yield potential. However, apart from the ACIAR/CIMMYT project looking at stomatal aperture-related traits as well as source and sink traits (Condon et al., in press; Reynolds et al., in press; van Ginkel et al., in press), there appear to have been few attempts to validate physiological (or morphological) selection criteria for wheat yield potential in the last decade, but recent promising results with spectral reflection indices could foreshadow more validation work. This contrasts with efforts to improve the performance of wheat (and maize) under water-limited conditions, and with the new plant type and super rice approaches of IRRI and China, respectively. Such research could be mapped out for wheat yield potential improvement, and could lead to more efficient breeding for yield potential and/or faster progress, but it requires a multidisciplinary team, including, nowadays, molecular biologists. It also needs suitable controlled and field environments and substantial long-term support. All this may no longer be available in the public sector, at least at a single location.

PAPER PRESENTED AT INTERNATIONAL WORKSHOP ON INCREASING WHEAT YIELD POTENTIAL, CIMMYT, OBREGON, MEXICO, 20–24 MARCH 2006 Sink limitations to yield in wheat: how could it be reduced?

Abstract: Ponencia presentada al International Workshop on Increasing Wheat Yield Potential, CIMMYT, Obregon, Mexic, del 20 al 24 de marc de 2006.

Prospects for increasing photosynthesis by overcoming the limitations of Rubisco

Abstract: The low activity and the competing reactions catalysed by Rubisco are major limitations to photosynthetic carbon assimilation in C3 plants; the present paper considers how these limitations can be overcome. The limitations could be most effectively addressed by introducing Rubisco with a higher catalytic rate and/or better able to discriminate between gaseous substrates. Although enzymes with desirable characteristics are available, technical advances are required before their potential can be realized in major crop plants. Significant improvements could be achieved also by increasing the concentrations of the productive substrates, CO2 and RuBP, at the active site of Rubisco. Critically, it is essential that other environmental and genotype constraints are minimized, to realize the highest photosynthetic potential.

Genetic progress in yield potential in wheat: recent advances and future prospects

Abstract: Knowledge of the changes in physiological traits associated with genetic gains in yield potential is essential to improve understanding of yield-limiting factors and to inform future breeding strategies. Recent advances in genetic yield potential and associated physiological changes in wheat (Triticum aestivum L.) are reviewed. Genetic gains in yield potential worldwide have been both positively correlated with harvest index (HI) and above-ground dry matter (AGDM), with more frequent reports of yield progress associated with biomass since about 1990. It is concluded that an important aim of future breeding will be the increase of biomass production while maintaining the present values of HI. In winter wheat recent biomass progress has been positively associated with pre-anthesis radiation-use efficiency (RUE) and water-soluble carbohydrate (WSC) content of stems at anthesis. Present results in two doubled-haploid (DH) populations show a positive linear relationship between stem WSC and grain yield in the UK environment. Results from various investigations worldwide in recent years have demonstrated that biomass increases have been associated with particular introductions of alien genes into wheat germplasm, e.g. the 1BL.1RS wheat-rye translocation and the 7DL.7Ag wheat-Agropyron elongatum translocation. Present results confirm a positive effect of 1BL.1RS on harvest biomass in two DH populations in the UK. The future prospects for identifying physiological traits to raise yield potential are considered with particular reference to winter wheat grown in northwestern Europe. It is proposed that optimized rooting traits, an extended stem-elongation phase, greater RUE, greater stem WSC storage and optimized ear morphology will be important for breeding progress in yield potential in future years.

Artificial neural networks for rice yield prediction in mountainous regions

Abstract: Decision-making processes in agriculture often require reliable crop response models. The Fujian province of China is a mountainous region where weather aberrations such as typhoons, floods and droughts threaten rice production. Agricultural management specialists need simple and accurate estimation techniques to predict rice yields in the planning process. The objectives of the present study were to: (1) investigate whether artificial neural network (ANN) models could effectively predict Fujian rice yield for typical climatic conditions of the mountainous region, (2) evaluate ANN model performance relative to variations of developmental parameters and (3) compare the effectiveness of multiple linear regression models with ANN models. Models were developed using historical yield data at multiple locations throughout Fujian. Field-specific rainfall data and the weather variables (daily sunshine hours, daily solar radiation, daily temperature sum and daily wind speed) were used for each location. Adjusting ANN parameters such as learning rate and number of hidden nodes affected the accuracy of rice yield predictions. Optimal learning rates were between 0·71 and 0·90. Smaller data sets required fewer hidden nodes and lower learning rates in model optimization. ANN models consistently produced more accurate yield predictions than regression models. ANN rice grain yield models for Fujian resulted in R2 and RMSE of 0·87 and 891 vs 0·52 and 1977 for linear regression, respectively. Although more time consuming to develop than multiple linear regression models, ANN models proved to be superior for accurately predicting rice yields under typical Fujian climatic conditions.

Conservation Agriculture in South Asia

Abstract: The Green Revolution era focused on enhancing the production and productivity of rice and wheat New challenges demand that the issues of efficient resource use and resource conservation receive high priority to ensure that past gains can be sustained and further enhanced to meet the emerging needs Extending some of the resource-conserving interventions developed for wheat to rice culture is a major challenge for researchers and farmers alike The present paper shares recent research experiences on resource conservation technologies involving tillage and crop establishment options and associated agronomic practices which enable farmers in reducing production costs, increase profitability and help them move forward in the direction of adopting conservation agriculture

Cassava improvement: challenges and impacts

Abstract: Cassava (Manihot esculenta Crantz) is one of the two most important food crops in sub-Saharan Africa. This area accounts for most of the root harvest worldwide, followed by Asia and Latin America - the centre of origin for Manihot species. In Africa and Latin America, cassava is mostly used for human consumption, while in Asia and parts of Latin America it is also used commercially for the production of animal feed and starch-based products. Cassava is regarded as a crop adapted to drought-prone environments, where cereals and other crops do not thrive, and it also grows well in poor soil. There are about 100 wild Manihot species, which provide an important genetic endowment for cassava breeding. Professional cassava breeding started in the 20th century and was spurred on by increasing population demands. The main breeding goals are high yield per unit area, particularly in marginal or pest-prone environments. The most notable results from cassava breeding are seen today in sub-Saharan Africa, where it has been transformed from a poor man's crop to an urban food, and in Southeast Asia, where it has changed from a subsistence crop to an industrial cash crop. Long-term research by many international and national partners has led to breeding high-yielding cassava cultivars that increased crop yields up to 40%. Manipulation of genes from wild species has led to new cultivars that resist prevailing diseases and pests, allowing the avoidance of large-scale famine in sub-Saharan Africa. Cassava improvement continues to tap genetic variation through conventional breeding (including the use of wild species) and biotechnology, because many pathogens still take their toll and occasionally epidemics affect farmer fields significantly. However, new sources of variation are needed to genetically enhance the nutritional quality of this important food crop in Africa and other areas in the tropics of the developing world.

Towards sustainable grassland and livestock management

Abstract: Grasslands are one of the world's major ecosystems groups and over the last century their use has changed from being volunteer leys, or a resource on non-arable land, to a productive resource equal to any crop and managed as such. Many grasslands are now being acknowledged as having a multifunctional role in producing food and rehabilitating crop lands, in environmental management and cultural heritage. However, grasslands across the globe are under increasing pressure from increasing human populations, reduced areas with increasing livestock numbers, and declining terms of trade for livestock production, and they are managed to varying degrees of effectiveness. The complexity of grassland uses and the many aspects of grassy ecosystems require a framework wherein solutions for better management can be developed. The present paper discusses a generic approach to grassland management to satisfy these multiple objectives. A focus on ecosystem functionality, i.e. on water, nutrient and energy cycling and on the biodiversity required to sustain those functions, provides a means of resolving the dilemmas faced, through the intermediary, management-related, criteria of herbage mass, which also relates directly to animal production. Emphasis is placed on the opportunities to satisfy multiple objectives. A consideration of the basic relationships between stocking rate and animal production shows that the longer-term, economically optimal stocking rate is associated with improved environmental outcomes. There may be environmental objectives that go beyond economically sustainable limits for livestock producers and in those cases direct payments from the government or others will be needed. These are likely to be where degradation is clearly apparent. The achievement of desirable outcomes in grassland management that satisfy multiple objectives will require new areas of research that seek viable solutions for farmers and society.

Nutritional manipulation of the fatty acid composition of sheep meat: a review

Abstract: Sheep meat is characterized as being high in saturated fatty acids and low in polyunsaturated fatty acids (PUFA), attributes that are regarded as being disadvantageous within the human diet. Despite fresh forage being a particularly rich source of 18:3n-3 and vegetable oils being high in 18:2n-6 and 18:3n-3, the process of biohydrogenation in the rumen generally results in proportionally less than 0·1 of these essential dietary fatty acids (FA) reaching the small intestine. Increases in muscle content of 18: 3n - 3 of 1-2-fold have been achieved by supplementation with oil, or oilseeds, whilst increases of 1-3-fold have been obtained from grazing grass compared with concentrates, but in general the polyunsaturated to saturated FA ratio (P:S) in sheep meat has remained low at approximately 0-2-0·3. Substantial improvements in the P:S ratio of up to 0·57 and increases in muscle and adipose tissue levels of 18:3n-3 of up to 4g/100g FA can be obtained, but rely on protecting dietary PUFA from biohydrogenation. Additionally, increasing tissue supply of 18:3n-3 will result in only a small improvement in muscle concentration of the nutritionally beneficial 20:5n-3 and 22:6n-3, with meaningful increases relying on a dietary supply of these very-long-chain PUFA. An alternative strategy to improve the human health attributes of sheep meat is to decrease tissue levels of 18:0 by increasing the activity of stearoyl-CoA desaturase (SCD), although the response is often relatively small. Despite the apparent negative impact of ruminal metabolism on muscle FA content, the process of biohydrogenation is often incomplete and several of the intermediaries can have positive effects on human health. Within these intermediaries, future increases in tissue content of cis-9, trans-11 conjugated linoleic acid (CLA) may be obtained by increasing tissue supply directly, although a greater response may be obtained by maximizing tissue supply of trans-11 18:1 and elevating the action of SCD. Production of a FA profile in sheep meat that is higher in PUFA, particularly the advantageous very-long-chain PUFA, and with flavour and eating characteristics that meet specific market preferences, is a suitable area for research.

Reduced nitrogen and improved farm income for irrigated spring wheat in the Yaqui Valley, Mexico, using sensor based nitrogen management

Abstract: Wheat nitrogen-use efficiency in the Yaqui Valley has been estimated at about 0·31. The nitrogen that is not recovered by the crop has important environmental costs that have regional and global consequences. In addition, these nitrogen losses represent an important reduction in farm income. The objective of the present work was to validate a technology that includes the use of N-rich strips together with the GreenSeeker™ sensor and a crop algorithm in farmers' fields with the ultimate goal of improving nitrogen-use efficiency through site-specific nitrogen management in irrigated spring wheat. During the wheat crop cycle 2002/03 and 2003/04, 13 validation experiments of c. 1 ha each were established in farmers' fields in the Yaqui Valley. After the validation phase, during the wheat crop cycle 2005/06, eight technology transfer trials were established in farmers' fields; these had on an average an area of 10 ha each. Both the validation and technology transfer trials compared the farmers' conventional nitrogen management use v. the use of the N-rich strip together with the Green Seeker™ sensor and a crop algorithm to derive N recommendations for each individual field. The results of the validation trials showed that on an average over all locations, farmers were able to save 69 kg N/ha, without any yield reduction. At the price of US56/ha, when averaged over all trials in all years.

Intercropping with pulses to concentrate nitrogen and sulphur in wheat

Abstract: The effects of intercropping wheat with faba bean (Denmark, Germany, Italy and UK) and wheat with pea (France), in additive and replacement designs on grain nitrogen and sulphur concentrations were studied in field experiments in the 2002/03, 2003/04 and 2004/05 growing seasons. Intercropping wheat with grain legumes regularly increased the nitrogen concentration of the cereal grain, irrespective of design or location. Sulphur concentration of the cereal was also increased by intercropping, but less regularly and to a lesser extent compared with effects on nitrogen concentration. Nitrogen concentration (g/kg) in wheat additively intercropped with faba bean was increased by 8% across all sites (weighted for inverse of variance), but sulphur concentration was only increased by 4%, so N:S ratio was also increased by 4%. Intercropping wheat with grain legumes increased sodium dodecyl sulphate (SDS)-sedimentation volume. The effect of intercropping on wheat nitrogen concentration was greatest when intercropping had the most deleterious effect on wheat yield and the least deleterious effect on pulse yield. Over all sites and seasons, and irrespective of whether the design was additive or replacement, increases in crude protein concentration in the wheat of 10 g/kg by intercropping with faba bean were associated with 25-30% yield reduction of the wheat, compared with sole-cropped wheat. It was concluded that the increase in protein concentration of wheat grain in intercrops could be of economic benefit when selling wheat for breadmaking, but only if the bean crop was also marketed effectively.

Boron application affects seed yield and seed quality of sugar beets

Abstract: Sugar beet (Beta vulgaris L.) is one of the most important sugar crops worldwide. Despite the fact that sugar beet crop has high requirements for boron (B), the effect of B applications on seed yield and on seed quality is not known. A 2-year field study was conducted to determine whether soil and foliar B applications during anthesis increase seed set, final seed yield and improve seed quality of sugar beets. Boron solutions were applied at four rates (0, 245, 490 and 735 mg/l of B) as foliar applications and at two rates (1·5 and 3 kg/ha of B) as soil applications to field plots exhibiting no vegetative symptoms of B deficiency. Foliar B application increased the concentration of B in vegetative and reproductive tissues much more than soil application. In addition, foliar B application increased the seed yield by an average of 10% in the first year and by an average of 44% in the second year. The mean seed weight was affected by B application as it was increased in both years. The proportion of larger seeds (>5·00 and 4·5–5·00 mm) increased with increasing application of B. Moreover, seed quality was affected and the proportion of abnormal seedlings was decreased with B application. However, seed vigour was not affected by B application. These data indicate that foliar B application can improve seed yield and seed quality of sugar beet grown for seed production. However, the physiological basis of this effect remains unknown.

Effects of soil compaction in potato (Solanum tuberosum) crops

Abstract: Since many soils used for growing potatoes in the UK are likely to be close to their plastic limit for cultivation during early spring, there exists the potential for soil compaction to occur during planting which will restrict root penetration. A series of experiments showed that soil compaction delayed emergence, reduced rate of leaf appearance and ground cover expansion, shortened canopy cover duration and restricted light interception, which combined to reduce tuber yield. Rooting density and maximum depth of rooting were reduced, particularly where compaction was shallow. In some soils, irrigation helped alleviate some of the effects of compaction but in others it exacerbated their severity. Using a cone penetrometer, relationships between rate of root penetration and soil resistance (Ω) were established from a number of experiments and replicated blocks in commercial fields and an overall relationship of the form y=16·3–4·08Ω mm/day was produced. Root penetration rates of c. 20 mm/day were measured in the intensively-cultivated ridge zone but growth rates were halved at a Ω of 1·5 MPa. A survey of 602 commercial fields showed that two thirds of fields had Ωs ⩾3 MPa (where root growth rates would be <2 mm/day) within the top 0·55 m of the soil profile. Thus, rooting depth is likely to be considerably shallower than desirable and lead to inefficiency of water and nutrient utilization. The use of powered cultivators to separate stones and clods from beds or ridges and produce a fine seedbed is now almost universally adopted in the UK. However, the system is both time and energy inefficient and increases the risk of creating soil compaction, particularly at shallow depths. All cultivation equipment has been shown to cause compaction and it is suggested that the consequences of the shortening of the growing season from delaying planting by a few days to allow the soil to dry are far less than the yield and quality losses caused by compaction.

Declining rapeseed yields in Finland: how, why and what next?

Abstract: Average seed yields per hectare of Brassica oilseed crops in Finland, mainly summer turnip rape (Brassica rapa L. var. oleifera subvar. annua), which covers 0·93–0·99 of the total oil crop cultivation area depending on year, have fallen dramatically during the last 15 years. This downward trend is contrary to those in other temperate regions, where rapeseed yields have increased or levelled off after reaching a relatively high level. The 5-year moving averages for Finland show that seed yield started to diminish gradually after reaching its highest level of over 1700 kg/ha in the early 1990s. By 2005 it had fallen to 1270 kg/ha. The present study evaluated the possible reasons for the recorded collapse in Finnish turnip rape yields. All the statistical analyses were based on large, previously produced, datasets from multi-location Agrifood Research Finland (MTT) Official Variety Tests, Finnish Food Safety Authority (EVIRA) Seed Testing datasets and the Information Centre of the Ministry of Agriculture and Forestry in Finland (TIKE) national production datasets. Results from MTT trials indicated that the latest turnip rape cultivars were more sensitive to elevated temperatures at late seed set and during seed fill – and such temperatures often occurred during the years of greatest yield reduction. When taking into account how commonly sown these cultivars were at national level during the last 10 years, increased sensitivity contributed to up to two thirds of the recorded yield reduction. Even though the growing area of turnip rape has slightly exceeded 100 000 ha, after long being 60 000–70 000 ha, by extending cultivation to more northern areas of Finland, such changes do not explain the yield collapse according to data from TIKE. Furthermore, lower national yields do not stem from larger, but rather are associated with narrower within year variation in seed yield. Additional empirical work is needed to understand the causes of increased temperature sensitivity in modern cultivars (e.g. possible linkage to drought, diseases and/or drastically increased seed energy content). Furthermore, a national survey is essential for a thorough and up-to-date picture of the prevalence of pests and diseases in turnip rape and their contribution to reduced yields.

Association of source/sink traits with yield, biomass and radiation use efficiency among random sister lines from three wheat crosses in a high-yield environment

Abstract: For many years yield improvement reported in wheat was associated with increased dry matter partitioning to grain, but more recently increases in above-ground biomass have indicated a different mechanism for achieving yield potential. The most likely way of increasing crop biomass is by improving radiation use efficiency (RUE); however there is evidence that sink strength is still a critical yield limiting factor in wheat, suggesting that improving the balance between source and sink (source/sink (SS)) is currently the most promising approach for increasing yield, biomass, and RUE. Experiments were designed to establish a more definitive link of SS traits with yield, biomass and RUE in high-yield environments using progeny deriving from parents contrasting in some of those traits. The SS traits formed three main groups relating to (i) phenological pattern of the crop, (ii) assimilation capacity up until shortly after anthesis, and (iii) partitioning of assimilates to reproductive structures shortly after anthesis. The largest genetic gains in performance traits were associated with the second group; however, traits from the other groups were also identified as being genetically linked to improvement in performance parameters. Because many of these traits are interrelated, principal component analysis (PCA) multiple regression and path analysis were used to expose these relationships more clearly. The trait most consistently associated with performance traits was biomass at anthesis (BMA). The PCA indicated a fairly close association among traits within this group (i.e. assimilation-related traits) while those from the other two groups of SS traits (i.e. phenological and partitioning) appeared to have secondary but independent effects. These conclusions were partially born out by stepwise multiple regression for individual crosses where BMA was often complemented by traits from the two other groups. Taken together, the data suggest that the assimilation traits biomass in vegetative stage (BMV) and BMA have partially independent genetic effects in this germplasm and were complementary to achieving improved performance. The identification of a number of SS traits associated with yield and biomass, which both PCA and multiple regression suggest as being at least partially independent of one another, support the idea that additive gene action could be achieved by adopting a physiological trait based breeding approach where traits from different groups are combined in a single background. A second breeding intervention based on these results would be in selecting progeny for BMA and BMV using spectral reflectance approaches since those traits that lend themselves to large-scale screening. Path analysis confirmed the importance of the spike primordial stage in the genotype by environment interaction for these traits.

The impact of climate change on sugarbeet yield in the UK: 1976-2004

Abstract: Since the 1970s, the delivered sugar yield per hectare has risen at an average annual rate of 0·111 t/ha, while the sugar yield in the official variety trials has increased at an average annual rate of 0·204 t/ha. These increases are usually considered to be the result of improvements in varieties and in beet agronomy. The present paper considers the possible impact of recent changes in climate on UK sugar yields by using the Broom's Barn Crop Growth Model and daily weather data collected over the last 30 years. Simulations of sugar yield using weather in eastern England since 1976 increased by an average annual rate of 0·139 t/ha, which accounted for about two thirds of the rate in the official variety trials. This increase was not an artefact of the accuracy of weather recording but it was, in part, accounted for by the trend to earlier sowing. Although it was not statistically significant, the earlier sowing trend was associated with an increase of 0·025 t/ha per year and was an indirect effect of the climate change. The annual deviations from these trends have not tended to become significantly bigger or smaller over the three decades. The model is not variety-specific, so it makes no allowance for variety improvements during the last 30 years. Clearly, varieties have improved so the implication must be that some of the changes in agronomy have tended to decrease the yields significantly. The changes in agronomic practice most likely to be responsible are the extension of the crop processing campaign, leading to greater post-harvest storage losses, and a decrease in the irrigated area.

Predictability of wheat growth and yield in light-limited conditions

Abstract: In seeking better predictions of grain yield under light-limited conditions, shading was applied to field-grown winter wheat cv. Slejpner during each of five consecutive phases (canopy expansion, ear expansion, pre-flowering, grain expansion and grain filling). Absolute measures were taken of solar radiation and its effects on growth in three seasons, at a site where water and nutrient supplies were not limiting. Replicate mobile shades automatically occluded 0·80 of incident light when mean total solar radiation exceeded 250 J/m2 per s. Mean effects over seasons of shading on incident total solar radiation were -296, -139, -78, -157 and -357MJ/m2 for the five phases respectively, and corresponding effects on shoot dry weight were- 236,- 184,- 58.-122 and - 105 g/m 2 Estimated efficiency of radiation use after flowering was 1·2 g/MJ unshaded, tending to increase with shading. Shading in all phases reduced grain dry matter yield: mean effects over seasons were -106, -64, - 61, - 93 and - 281 g/m 2 for the five consecutive shading periods. Shading from GS31-39 increased mean maximum area of the two top leaves from 2700 to 3100 mm 2 per leaf but, with fewer stems, canopy size remained unaffected. This and the next shading. from GS39-55, reduced specific leaf weight from 42 g/m 2 by 4 and 3 g/m 2 respectively, but effects on shoot dry weight were largely due to stem and ear. By flowering, stem weights, and especially their reserves of water-soluble carbohydrates, had partially recovered. Effects on yield of shading from GS31-39 were explained by a reduction in grains/m 2 of 3070 from 26 109. Shading from GS39-55 reduced grains/m 2 by 4211 due to fewer grains per ear, whilst mean weight per grain increased in compensation. Shading from GS55 -61 decreased grains/ear by 2·5. Shading from GS61-71 decreased ear growth and redAced stem weight, and at harvest resulted in 4·3 less grains/ear. Effects of the final shading from GS71-87 were fully explained by a reduction in mean dry weight/gram of 10-3 mg. Except for shading from GS71-87 source- and sink-based explanations of grain yield both proved feasible, within the precision of the measurements. Constraints to accurate comparison of source- and sink-based approaches are identified, and the implications for yield forecasting are discussed.

The distribution of urine deposited on a pasture from grazing animals

Abstract: Intensive agricultural production practices are known to cause far-reaching effects on water quality. The current paper addresses and quantifies these effects caused by high stocking rates.A set of stochastic difference equations describing the development of the proportion of a grazed field either unaffected by urine deposition, or affected by multiple (1, 2, …) urine depositions is described. A solution to this set of equations is found for the expected value of multiple (0, 1, 2, …) urine depositions, and the variances of these depositions. It is assumed that an animal voids urine with a Poisson probability distribution, and that each urine deposition covers a random area with a Gaussian probability density. Given these reasonable assumptions, the probability distributions for each multiplicity of patch distribution can be found numerically.The utility of the results obtained is illustrated for a problem in assessing the nitrogen (N) pollution of ground water from different grazing strategies. It is demonstrated quantitatively that mob stocking (typical of winter management regimes in New Zealand) is often caused by rotational grazing. The latter is often used to optimize grass growth and intake, especially in winter. This increases (more than linearly) the level of N pollution in ground water. This is because of the increased frequency of multiple urine depositions, i.e. more than one urine deposition on the same patch of land in a short time.

Use of spatial analyses for global characterization of wheat-based production systems

Abstract: CIMMYT (International Maize and Wheat Improvement Centre) and other research groups within the Consultative Group for International Agricultural Research (CGIAR) have made major contributions to agricultural development, e.g. underpinning the 'green revolution', but it is unlikely they will continue making such far-reaching contributions without the ability to collect, analyse and assimilate large amounts of spatially orientated agronomic and climatic data. Increasingly, application of modern tools and technologies are crucial elements in order to support and enhance the effectiveness of international agricultural research. Bread and durum wheats (Triticum aestivum and Triticum durum) occupy an estimated 200 million ha globally, are grown from sea level to over 3500 m asl, and from the equator to latitudes above 60 ° N in Canada, Europe, and Asia. For organizations like CIMMYT, which seek to improve wheat production in the developing world, understanding the geographic context of wheat production is crucial for priority setting, promoting collaboration, and targeting germplasm or management practices to specific environments. Increasingly important is forecasting how the environments, and their associated biotic and abiotic stress patterns, shift with changing climate patterns. There is also a growing need to classify production environments by combining biophysical criteria with socio-economic factors. Geospatial technologies, especially geographic information systems (GIS), are playing a role in each of these areas, and spatial analysis provides unique insights. Use of GIS to characterize wheat production environments is described, drawing from examples at CIMMYT. Since the 1980s, the CIMMYT wheat programme has classified production regions into mega-environments (MEs) based on climatic, edaphic, and biotic constraints. Advances in spatially disaggregated datasets and GIS tools allow MEs to be characterized and mapped in a much more quantitative manner. Parallel advances are improving characterizations of the actual (v. potential) distribution of major crops, including wheat. The combination of improved crop distribution data and key biophysical data at high spatial resolutions also permits exploring scenarios for disease epidemics, as illustrated for the stem rust race Ug99. Availability of spatial data describing future climate conditions may provide insights into potential changes in wheat production environments in the coming decades. There is a pressing need to advance beyond static definitions of environments and incorporate temporal aspects to define locations or regions in terms of probability or frequency of occurrence of different environment types. Increased availability of near real-time daily weather data derived from remote sensing should further improve characterization of environments, as well as permit regional-scale modelling of dynamic processes such as disease progression or crop water status.

Impact of uncertainty on the optimum nitrogen fertilization rate and agronomic, ecological and economic factors in an oilseed rape based crop rotation

Abstract: Crop yield and optimum nitrogen fertilization rates (Nopt) are often calculated ex post by specific functions of the nitrogen fertilization rate, but in doing this, uncertainties in terms of model choice, annual nitrogen response variations and parameter estimation are neglected. In the present study, Nopt, grain yields, net revenues and N balances were estimated for the three crops of an oilseed rape (OSR)–winter wheat–winter barley rotation. The effects of uncertainties were considered using three different statistical models, estimating an identical Nopt over the years and carrying out Monte-Carlo simulations where model parameters were varied according to their estimated standard errors. The statistical models used were the quadratic (Q) polynomial function, the linear response and plateau (LRP) function and the quadratic response and plateau (QRP) function.The Q model tended to estimate the highest Nopt values for the three crops, followed by the QRP and the LRP model in an initial ex post analysis. The highest corresponding mean net revenues in the rotation were estimated by the LRP model, followed by the Q and QRP model; mean N balances increased in the order LRP, QRP and Q. In the comparison of the crops, OSR showed the highest N balances followed by wheat and barley. Considering the protein concentration in wheat, Nopt values estimated by the Q model were considerably higher than without the economic effects of grain quality.In order to consider uncertainties in annual nitrogen response, an ex ante Nopt over the years was determined by maximizing the cumulated net revenues over all years in the rotation. Ex ante Nopt was higher as the mean of the ex post Nopt values for the QRP and LRP model. Average grain yields and net revenues were lower, N balances were higher. Running the Monte-Carlo simulations, ex post Nopt was obtained by 10 000 generated functions in each year and ex ante Nopt by 50 000 generated functions of years 1996, 1997, 1998, 1999 and 2002. This led to an increase in Nopt especially for the LRP model, while effects on the estimation of Nopt by the Q model were rather small. For the LRP model, corresponding mean net revenue decreased and mean N balance rose. In contrast, due to marginal changes in Nopt, the consideration of uncertainties in the estimations had only a small effect on net revenue and N balance in the Q model.In general, all kinds of uncertainty tended to increase Nopt but this effect was much higher for the LRP model as compared to the Q model. This increase in Nopt was associated with decreasing net revenues and increasing N balances. Exceptionally in OSR using the Q model, however, the ex ante approaches considering uncertainty led to slightly lower Nopt values compared to the ex post value.

An economic assessment of the use of physiological selection for stomatal aperture-related traits in the CIMMYT wheat breeding programme

Abstract: Physiological research has shown that measurements on small plots of stomatal conductance, canopy temperature depression (CTD) or carbon isotope discrimination may be useful for screening breeding populations for yield potential, prior to the execution of expensive replicated yield trials. Such indirect selection criteria may be very effective as lower cost alternatives for estimating genetic gain for complex characteristics such as yield that are relatively expensive to measure accurately in the field. In the present paper, economic analysis is undertaken of the results of trials conducted at the International Maize and Wheat Improvement Center (CIMMYT) over three seasons to determine the value of the physiological traits being assessed. The results indicate that the economic value of incorporating these measurements into CIMMYT's breeding programme is potentially important. CTD and stomatal conductance are relatively cheap to measure and could be used to discard lines prior to extensive yield testing, whereas carbon isotope discrimination is relatively expensive and would not be economic for this purpose. The analysis indicates that the incorporation of physiological measurements is likely to provide important economic benefits to the programme. Indications are that other breeding programmes with similar breeding goals and comparable costing structures might also consider using such indirect selection traits.

Winter survival of pea, faba bean and white lupin cultivars in contrasting Italian locations and sowing times, and implications for selection

Abstract: Increasing grain legume yields via autumn sowing requires winter-hardy material. Forty-nine pea, 24 faba bean and 11 white lupin cultivars recently released by 29 breeding institutions worldwide were sown in autumn 2002 at Lodi (northern Italy) and Foggia (southern Italy) on two different dates at each location, with the objective of assessing the winter survival of species and cultivars, its consistency across locations and sowing times, its relationship with grain yield and various morphophysiological traits and the implications for selection. The winter seasons were representative for the sites and had 54 frost days and −7·3°C absolute minimum temperature in Lodi, and 8 frost days and −3·4°C absolute minimum temperature in Foggia. The species differed in optimal sowing time at each location. Mild winter temperatures, preventing a sufficient hardening against late frosts, led to higher proportions of plants killed over winter in Foggia than in Lodi (0·17 v . 0·12 for pea; 0·20 v . 0·16 for faba bean; 0·34 v . 0·11 for lupin). Variation in winter mortality was much larger within species than among species. Winter mortality and grain yield of cultivars were inversely correlated ( r =−0·49, −0·43 and −0·74 for entry means over locations of pea, faba bean and lupin, respectively). The consistency across environments of genotype winter mortality, estimated by genetic correlations, was high across sowing times and low across locations for faba bean, moderate across sowing times and fairly low across locations for pea, and always fairly high for lupin. A visual cold tolerance score was always related to better winter survival. Winter survival tended to correlate with larger seeds in faba bean and lupin, and was associated with later flowering in lupin. A rosette-like winter growth habit (defined by lower height/number of leaves ratio of seedlings in January) was correlated with winter survival in all species (after partialling out the influence of seed size in faba bean and lupin). The optimal index of indirect selection for low winter mortality included the cold tolerance score, the seedling height/number of leaves ratio and the seed size for faba bean, the first two of these variables for pea, but only the first variable for lupin. The gain in predicted efficiency over direct selection was high for faba bean (29%) and modest for pea and lupin (⩽10%).

Genetic variation and correlation among yield and quality traits in cocksfoot (Dactylis glomerata L.)

Abstract: The objective of the present research was to study the genetic variability for total dry matter (DM) yield, tiller number, heading date and three quality traits, namely content of digestible dry matter (DDM), water-soluble carbohydrate (WSC) and crude protein (CP), in cocksfoot (Dactylis glomerata L.). Twenty-five parents were randomly chosen from a genetically broad-based population, and their respective half-sib (HS) families were generated. Clonally-propagated parents and their HS family seeds were grown as individual plants using a randomized complete block design with two replications in Alborz Research Center, Karaj, Iran, during 2002–04. The results of combined analyses over 2 years showed significant variances between clonal parents for all traits except CP. In the HS generation, between-family variances were only significant for tiller number, heading date and WSC. Clone×year (S2GY) and family×year (S2FY) interactions were significant for all traits except for WSC in HS families. The estimates of broad-sense heritability (h2b) were moderate to high for all traits (h2b=0·37–0·69), except CP. Narrow-sense heritability (h2n) estimates from analyses of progenies and from regression of HS progenies on parents (h2op) were moderate, relatively the same values as h2b for heading date, tiller number and WSC, which suggested that additive genetic variance was the main component controlling these traits. For DM yield and DDM, h2n and h2op estimates were low, whereas h2b estimates were moderate, which suggested that both additive and non-additive gene effects played an important role in the genetic regulation of these traits. Genetic correlations among CP with both WSC and DDM were generally negative, whereas WSC was positively correlated with DDM and tiller number. The genetic correlation among DM yield with DDM was weak and inconsistent and, in general, negative. DM yield had negative and positive correlation with heading date and tiller number, respectively. It was concluded that there was significant variation and moderate heritability for most traits in the cocksfoot populations evaluated to improve yield and quality traits. Selection for high WSC is a means to improve quality in general. The data also indicate that response to combined selection for both DDM and DM yield should be possible. Selection for DDM alone could result in reduction in yield.

PAPER PRESENTED AT INTERNATIONAL WORKSHOP ON INCREASING WHEAT YIELD POTENTIAL, CIMMYT, OBREGON, MEXICO, 20–24 MARCH 2006 Use of spatial analyses for global characterization of wheat-based production systems

Abstract: CIMMYT (International Maize and Wheat Improvement Centre) and other research groups within the Consultative Group for International Agricultural Research (CGIAR) have made major contributions to agricultural development, e.g. underpinning the ‘green revolution’, but it is unlikely they will continue making such far-reaching contributions without the ability to collect, analyse and assimilate large amounts of spatially orientated agronomic and climatic data. Increasingly, application of modern tools and technologies are crucial elements in order to support and enhance the effectiveness of international agricultural research. Bread and durum wheats (Triticum aestivum and Triticum durum) occupy an estimated 200 million ha globally, are grown from sea level to over 3500 m asl, and from the equator to latitudes above 60 ° N in Canada, Europe, and Asia. For organizations like CIMMYT, which seek to improve wheat production in the developing world, understanding the geographic context of wheat production is crucial for priority setting, promoting collaboration, and targeting germplasm or management practices to specific environments. Increasingly important is forecasting how the environments, and their associated biotic and abiotic stress patterns, shift with changing climate patterns. There is also a growing need to classify production environments by combining biophysical criteria with socio-economic factors. Geospatial technologies, especially geographic information systems (GIS), are playing a role in each of these areas, and spatial analysis provides unique insights. Use of GIS to characterize wheat production environments is described, drawing from examples at CIMMYT. Since the 1980s, the CIMMYT wheat programme has classified production regions into mega-environments (MEs) based on climatic, edaphic, and biotic constraints. Advances in spatially disaggregated datasets and GIS tools allow MEs to be characterized and mapped in a much more quantitative manner. Parallel advances are improving characterizations of the actual (v. potential) distribution of major crops, including wheat. The combination of improved crop distribution data and key biophysical data at high spatial resolutions also permits exploring scenarios for disease epidemics, as illustrated for the stem rust race Ug99. Availability of spatial data describing future climate conditions may provide insights into potential changes in wheat production environments in the coming decades. There is a pressing need to advance beyond static definitions of environments and incorporate temporal aspects to define locations or regions in terms of probability or frequency of occurrence of different environment types. Increased availability of near real-time daily weather data derived from remote sensing should further improve characterization of environments, as well as permit regional-scale modelling of dynamic processes such as disease progression or crop water status.

Validating the alkane pair technique to estimate dry matter intake in equids

Abstract: The estimation of dry matter intake (DMI) using the alkane pair technique has been validated in ruminants, but not in equids. The current paper reports the finding of three comparative validation studies carried out using a total of 12 cattle, 29 donkeys and 10 horses during which directly measured intake was compared to estimated intake using the alkane pair technique. Two methods were developed to dose the even chain alkanes that were used as external markers. Study I, carried out in Zimbabwe, compared the accuracy of estimated intake with measured intake in cattle and donkeys using hexatriacontane (C36) as the external marker. Studies II and III were carried out in the UK with horses and donkeys and compared the accuracy of estimated intake with measured intake using dotriacontane (C32) as the external marker. Study III also tested the effect on the accuracy of intake estimates of two marker dosing levels (mean daily dose of 224 mg per animal and 448 mg per animal) and two dosing frequencies (2× and 3× daily). Twice daily dosing of even-chain alkane at the lower dose level provided an estimate of DMI similar to that obtained by thrice daily dosing at this low level. The higher dose level given twice daily tended to produce large variation in faecal concentrations of dosed even-chain alkanes, this variation was reduced when dosing frequency was increased to thrice daily. The accuracy of estimated intake improved progressively as the number of faecal sampling days was increased from one to six with no significant difference between estimated intake based on day 5 or 6 of faecal sampling. The results of all three studies indicate that the alkane pair technique provides a robust method of estimating intake in equids with no significant difference between measured and estimated values in all but one case. Using C31 as an internal marker provided a more accurate estimated intake than using C33 as the internal marker in all cases. Faecal recoveries of alkanes in equids do not appear to show the same influence of carbon chain length that has been observed in ruminant studies. © 2007 Cambridge University Press.

Influence of short-term Leucaena leucocephala feeding on milk yield and its composition, thyroid hormones, enzyme activity, and secretion of mimosine and its metabolites in milk of cattle

Abstract: Four Karan/Friesian crossbred (Holstein×Tharparkar) dairy cows in late lactation (>200 days) were fed a basic diet of green maize and concentrates with an increasing proportion of Leucaena leucocephala (leucaena) leaf meal (LLM). The proportion was gradually increased from 0·25 of the dry matter intake (DMI) in the first week to 0·50 in the second, 0·75 in the third and ad libitum in the fourth week. Mimosine, 3,4-dihydroxy pyridine (3,4-DHP) and 2,3-dihydroxy pyridone (2,3-DHP) levels were determined in milk, serum, urine and faecal samples. On average DMI of leucaena was 0·023–0·025, 0·025–0·027, 0·027–0·028 and 0·022–0·025 of live weight (LW) during the first, second, third and fourth week, respectively. Mimosine, 3,4-DHP and 2,3-DHP appeared in the blood serum during leucaena feeding and continued appearing up to sixth week of experimental feeding even after the withdrawal of leucaena from the 34th day onwards. Similarly, excretion of mimosine, 3,4-DHP and 2,3-DHP were observed even after withdrawal of leucaena from the diet. The feeding of LLM resulted in a reduced level of T3 (Triiodothyronine) and T4 (Thyroxine) within a week of LLM feeding. The level of T3 and T4 improved to normal after withdrawal of LLM from the diet. The serum aspartate transferase (AST) and serum alanine transferase (ALT) activities were within the normal range. Leucaena feeding improved milk yield and composition only up to 3 weeks of feeding. The concentration of mimosine, 3,4-DHP and 2,3-DHP in milk was 0·33, 0·05 and 0·02 that of blood, respectively. The secretion of mimosine, 3,4-DHP and 2,3-DHP in the milk might be a concern for health of the offspring of leucaena-fed animals as well as human beings consuming such milk.

Challenges to international wheat improvement

Abstract: Wheat is grown on 210 million ha throughout the world producing approximately 600 million tonnes of grain (10 year average; FAO 2005) and providing on average one fifth of the total calorific input of the world's population (FAO 2003). For some regions such as North Africa, Turkey and Central Asia, wheat provides half of total dietary energy intake. Of the cultivated wheat area, half is located in less developed countries where there have been steady increases in productivity since the green revolution, associated with genetic improvements in yield potential, resistance to diseases and adaptation to abiotic stresses (Reynolds & Borlaug 2006a, b) as well as better agronomic practices (Derpsch 2005). Nonetheless, challenges to wheat production are still considerable, especially in the developing world, not only because of increased demand but also because of the increased scarcity of water resources (Rosegrant 1997; WMO 1997), ever more unpredictable climates (Fischer et al. 2002), increased urbanization and loss of good quality land away from agriculture (Hobbs 2007), and decreased public sector investment in agriculture and rural affairs (Falcon & Naylor 2005). To meet demand in a sustainable way, more resources are required to breed a new generation of genetically improved cultivars as well as implement resource-conserving agronomic management practices.

Estimates of heterosis and association of genetic distance with heterosis in durum wheat under different moisture regimes

Abstract: The objectives of the present study were to evaluate heterosis for grain yield and yield components in durum wheat, and to assess the prediction potential of amplified fragment length polymorphism (AFLP) based and agronomic trait based genetic distances (GD and MD, respectively) to F 1 performance, mid parent heterosis (MPH), and specific combining ability effects (SCA) under well-watered and moisture stress conditions. Six parental genotypes with different responses to moisture stress and their 15 F 1 crosses were evaluated for their responses to moisture stress conditions in a glasshouse. Some cross combinations showed significant MPH for grain yield and yield components. The expression of heterosis for grain yield was greater under moisture stress conditions than under well-watered conditions. Cluster analysis of the parental lines based on agronomic performance under stress conditions was similar to cluster analysis result based on AFLP marker profiles. F 1 performance was strongly correlated to both SCA effects and MPH under both stress and well water conditions. The correlation between SCA and MPH was very high under both treatment conditions for all traits. Correlation between GD and MD was significant only under stress conditions. Positive correlation was found only for the association between GD v. F 1 performance and GD v. SCA effects for harvest index (HI) under well-watered conditions. None of the correlations between MD and SCA effects were significant. The absence of association between GD and heterosis for yield and most agronomic traits implied that heterozygosity per se diversity is not a good predictor of heterosis or F 1 performance under both well-watered and stressed conditions.

U-impact pathway for diagnosis and impact assessment of crop improvement

Abstract: Agricultural research has contributed enormously to poverty reduction and increased food security worldwide. Wheat crop improvement is a good example of this contribution. Public investments in wheat research from the Green Revolution onwards led to significant productivity increases: following the widespread adoption of semi-dwarf varieties, annual yield growth rates peaked at 2-75% p.a. in the 1980s. Since then, public and private investments in crop (including wheat) research have been modest despite the potential of such research to contribute substantially to the first Millennium Development Goal (MDG) of halving hunger and poverty by 2015. Drawing on a wide spectrum of recent literature, the present paper broadens the usual frame of reference for diagnosing the adoption of improved technology and measuring impact. The adoption of improved varieties and management practices is influenced on the supply side by the nature and performance of the input delivery pathway from research to the farm (input value chains), and on the demand side by the characteristics of the farm household system and the marketing or value-adding chains from the farm to the consumer (output value chains). These three elements (input value chains, farm household system characteristics, and output value chains) can be viewed as a U-impact pathway. This pathway determines the rate and extent of adoption of improved varieties and practices, the magnitude of direct and indirect impacts, and the potential for feedback loops leading to improved functioning of the input and output value chains. The U-impact pathway provides a framework to identify an expanded set of beneficiaries from crop improvement which extend beyond the common focus on producers and final consumers; conventional surplus analysis can then be used to estimate the wider benefits to crop improvement. Additional metrics may be needed to estimate impact related to non-economic benefits, such as poverty, health and social capital. The implication of this fuller accounting of impacts is that the benefits accruing to agricultural research may be greater, and more widely distributed across the economy, than previously recognized by research managers and policy-makers. This strengthens the case for maintained or increased public and private sector investment in crop improvement.