Showing papers in "The Journal of Agricultural Science in 2001"

Emissions of ammonia, nitrous oxide and methane from different types of dairy manure during storage as affected by dietary protein content

Abstract: In a storage experiment with dairy cow manure, the effects of dietary protein content and manure type on ammonia, nitrous oxide and methane volatilization as well as overall nitrogen (N) loss from manure were investigated. Early-lactating cows received rations with 175, 150 and 125 g crude protein/kg dry matter. Each ration was tested in four manure storage systems reflecting typical farm conditions. These either contained total excreta with high amounts of straw (deep litter manure) or no straw (slurry) or, proportionately, 0.9 of urine and 0.1 of faeces (urine-rich slurry) complemented by the residuals with a low amount of straw (farmyard manure). Manure samples were stored for 7 weeks under controlled conditions and trace gas emission was repeatedly measured. Reduction of N intake decreased daily N excretion and urine N proportion and, on average, led to 0.7-fold lower storage ammonia emission rates on average. Total storage N loss was simultaneously reduced with the extent depending on urine N proportion of the respective manures. A lower dietary protein content furthermore reduced nitrous oxide emission rates in most manure types but increased methane emission from urine-rich slurry; however, global warming potential (based on trace gas output) of all manures was similar with low and high dietary protein content. In deep litter manure, characterized by the highest C: N ratio, emission rates of total N, ammonia and methane were lowest, whereas nitrous oxide values were intermediate. Substantial emission of nitrous oxide occurred with farmyard manure which also had the highest methane values and, consequently, by far the highest global warming potential. C:N ratio of manure was shown to be suitable to predict total N loss from manure during storage in all manure types whereas urine N proportion and manure pH were only of use with liquid manures.

Biohydrogenation and digestion of long chain fatty acids in steers fed on different sources of lipid

Abstract: Scollan, N. D., Dhanoa, M. S., Choi, N.-J., Maeng, W. J., Enser, M., Wood, J. D. (2001). Biohydrogenation and digestion of long chain fatty acids in steers fed on different sources of lipid. Journal of Agricultural Science, 136, (3), 345-355

Potential importance of water status traits for durum wheat improvement under Mediterranean conditions

Abstract: Water status traits have been proposed as criteria for drought tolerance improvement in several species especially in bread wheat, oat and barley. In order to test this possibility in durum wheat, in 1995 and 1997, a collection of 144 genotypes from different geographical origins was cultivated under rainfed Mediterranean conditions in Montpellier (southern France). Relative water content (RWC), osmotic potential (OP), as well as leaf morphological traits, grain yield (GY), total above-ground biomass and harvest index (HI) were measured. Large genotypic variations were observed for all traits. Differences between the 2 years were also noticed for all the traits which could be attributed to differences in water availability between the 2 growing seasons. The correlation analysis has revealed significant positive associations between water status traits and both GY and HI within and across years. These results suggest that genotypes which can maintain higher water status and then higher transpiration rates during grain filling, are more efficient in dry matter partitioning to grain and hence higher yield. Heritabilities of water status characters were higher than those of productivity traits. Our results emphasized the value of RWC and OP as criteria for durum wheat grain yield improvement under rainfed Mediterranean conditions. Relationships between RWC, OP and flag leaf morphological traits are also discussed.

Effect of timing of drought stress on growth and grain yield of extra-short-duration pigeonpea lines

Abstract: Four extra-short-duration (ESD) pigeon pea (Cajanus cajan) lines in 1991 and eight ESD lines in 1992 were grown with adequate soil moisture throughout their growth or subjected to drought coinciding with the vegetative, flowering and pod-filling stages under rainout shelters (India). In both years, drought stress treatments significantly reduced dry matter accumulation and seed yield. The extent of reduction in seed yield varied with the line and stage of stress imposition. Drought stress at the flowering stage caused greater reduction in total dry matter and seed yield than the stress imposed during the preflowering and pod-filling stages. Drought stress coinciding with the flowering stage reduced seed yield by 40-55% in 1991 and 15-40% in 1992 in different lines. ESD genotypes could extract moisture from up to a metre depth during preflowering and flowering stage stress but less during the pod-filling stage stress. Genotype ICPL 88039, followed by ICPL 89021, consistently showed the lowest sensitivity to drought stress at flowering. Protracted drought stress commencing from the preflowering to flowering or from the flowering to pod-filling stages was more harmful than stress at the individual stages. The reduction in yield under drought stress could be attributed mainly to less total dry matter accumulation, but also increased abscission of plant parts. The results suggest variation in sensitivity of ESD lines in relation to timing of stress, which should facilitate targeted screening for different intermittent moisture stress environments

Effect of variety, irrigation regime and planting date on depth, rate, duration and density of root growth in the potato (Solanum tuberosum) crop

Abstract: Experiments were conducted over the period 1987–94 at Cambridge University Farm and two other sites to examine the effect of various husbandry factors, particularly variety and irrigation regime, on rate, depth and density of rooting in potatoes. Maximum rooting depth ranged from 59 to 140 cm, indicating that potatoes can root to considerable depths and thereby have access to large volumes of water to satisfy the potential demand for water created by the atmospheric conditions and the size of the canopy. Root extension vertically through the soil profile was best described as a three-phase process: an initial rapid period lasting 3–5 weeks with growth rates c. 1·2 cm/day, a second period of slower growth (c. 0·8 cm/day), followed by cessation of root extension for the rest of the life of the crop. Variety had a major influence on the ultimate depth of rooting, primarily owing to variations in the length of the different periods of rooting rather than the rate in each period. It was observed that changes in the rate, or the cessation of root penetration were always preceded 4–9 days earlier by a change in the rate, or cessation, of leaf appearance. This feature should make it possible to characterize the duration of rooting of varieties through measurement of leaf emergence. Varieties which ceased leaf production early, such as Atlantic, were found to have a duration of root growth of c. 60 days, with Cara rooting for c. 30 days longer. Maximal total root length (TRL) and root length density (RLD) in the experiments reported were 16·9 km/m2 and 5·5 cm/cm3, respectively, similar to those found previously in potatoes and crops such as sugar beet, but considerably greater than many other vegetables. Rooting density decreased with depth, but the root systems were not as surface-oriented as many other studies have shown. When TRL was close to its maximum, the vertical distribution of RLD showed that between 40 and 73% was confined to the upper 30 cm, with irrigated crops possessing a greater proportion of their roots in the plough layer. Despite being planted in rows 70–91 cm apart, rooting systems were homogeneously distributed in a horizontal direction by c. 35 days after emergence, at which time the roots had reached a depth of c. 50 cm. Therefore, apart from a short period after emergence, the potato crop is capable of accessing considerable volumes of soil from which to extract water and nutrients. Ensuring that soil conditions are conducive to maximal rates of root growth should be the target for growers, since this will lead to a more efficient use of soil water and irrigation.

Effect of phosphorus fertilization and foliar application of chelated zinc and calcium on seed, protein and oil yields and oil properties of cotton

Abstract: Field experiments were conducted during two successive seasons in the Agricultural Research Center, Giza, Egypt (a clay loam soil), to study the effects of phosphorus fertilization (addition at rates of 44 and 74 kg of P 2 O 5 /ha) and foliar application of zinc (at 0.0 and 40 ppm of Zn applied twice, 75 and 90 days after planting) and calcium (at 0.0, 20, 40, and 60 ppm of Ca applied twice, 80 and 95 days after planting) on seed, protein and oil yields and oil properties of the Egyptian cotton cultivar Giza 75. Application of P at the high rate and spraying plants with zinc and calcium at any concentration increased cottonseed yield/ha, seed index, seed oil content, oil and protein yields/ha, seed oil unsaponifiable matter, and total unsaturated fatty acids (oleic and linoleic). Conversely, decreases in oil acid value, saponification value and total saturated fatty acids occurred. The seed protein and oil refractive index tended to increase when the high P rate and Zn were applied. Seed protein content tended to decrease slightly with Ca application. Regardless of the slight decrease in protein content as a result of Ca application, the yield of protein increased, due to the fact that there was an obvious increase in seed yield which counterbalanced the negative effect of the decrease in protein content. The highest Ca concentration (60 ppm) gave the highest values of cottonseed yield/ha, seed index, seed oil and protein yields/ha and oil unsaponifiable matter, followed by the concentration of 40 ppm. The concentration of 40 ppm gave the lowest total saturated fatty acids. The effect of Ca concentrations on oil refractive index was very limited.

Effect of dietary condensed tannins on gastrointestinal nematodes.

Abstract: It has been previously shown in this laboratory that feeding a model condensed tannin, quebracho tannin, reduces the small intestinal nematode burden in sheep and rats. The aim of the current programme was to determine whether this occurs through direct toxicity against the parasites. Both in vivo and in vitro studies were conducted. The first study compared the effect of dietary quebracho tannin (40 g/kg) on the establishment of the parasitic nematodes Nippostrongylus brasiliensis and Trichinella spiralis in the rat small intestine. The burden of N. brasiliensis, which, although closely associated with the mucosa, actually dwells within the small intestinal lumen, was significantly reduced (P 0·05) by the dietary inclusion of quebracho tannin. The second study involved monitoring the survival of adult N. brasiliensis and T. spiralis when incubated in vitro in varying concentrations of quebracho tannin in Hanks’ balanced salt solution. The survival of N. brasiliensis was compromised at concentrations as low as 0·01% (w/v) quebracho tannin but improved with the addition of 0·1% (w/v) polyethylene glycol, which binds to, and inactivates, tannin. T. spiralis was similarly affected, but much more rapidly. These results suggest that dietary quebracho tannin may reduce nematode worm burdens through a toxic effect that requires direct contact between parasite and tannin. This raises the possibility that feeding locally available plant material containing condensed tannins may be an alternative method for controlling parasite infections, especially in areas such as the tropics and subtropics.

Nitrate leaching and growth of cereal crops following cultivation of contrasting temporary grasslands

Abstract: Intensive dairy farming with low N use efficiencies may have adverse environmental impact through nitrate leaching. The residual effects of six different temporary grasslands (1994-96) on yield and nitrate leaching in the following cereal crops (1997-99) were investigated on a loamy sand in central Jutland. The grasslands were unfertilized grass-clover and fertilized ryegrass subject to cutting or continuous grazing by dairy cows with two levels of N in feed supplements. In the first year there was sufficient residual effect of the grazed grasslands to obviate the need for supplementary fertilizer, but in the following years gradually more fertilizer N was required to obtain optimal yields. Nitrate leaching decreased as a function of time after cultivation of grassland, but grassland management had little effect on the subsequent nitrate leaching (6 to 36 kg N/ha in unfertilized plots). Application of cattle slurry to cereals influenced nitrate leaching more than the history of the grassland and caused the annual mean nitrate concentration to exceed the EU Drinking Water Directive upper limit in most cases. Presumably, large differences in N-input during the grassland phase of the crop rotation had relatively little effect on the subsequent N release because of variable N losses during grazing. Possibilities for further improvement of the utilization of grassland N following cultivation are limited when the current knowledge has been implemented. If the N use efficiency of dairy farming systems is to be further improved the utilization of N during the pasture phase is crucial.

The effects of ploidy and a phenotype conferring a high water-soluble carbohydrate concentration on carbohydrate accumulation, nutritive value and morphology of perennial ryegrass (Lolium perenne L.)

Abstract: Smith, K. F., Simpson, R. J., Culvenor, R. A., Oram, R. N., Humphreys, M. O., Prud'homme, M. P. (2001). The effects of ploidy and a phenotype conferring a high water-soluble carbohydrate concentration on carbohydrate accumulation, nutritive value and morphology of perennial ryegrass (Lolium perenne L.). Journal of Agricultural Science, 136, 65-74.

The ability of wheat cultivars to withstand drought in UK conditions: resource capture

Abstract: Experiments in three dry seasons (1993/94, 1994/95, 1995/96) on a loamy medium sand at ADAS Gleadthorpe, Nottinghamshire, England tested responses of green area, radiation interception, water uptake and above-ground dry matter growth of six wheat cultivars to irrigation. Cultivars differing in date of introduction (Haven 1987, Maris Huntsman 1969, Mercia 1983, Rialto 1991, Riband 1985 and Soissons 1989) were chosen for contrast in flowering time and maximum green area. Maximum soil moisture deficit (SMD) exceeded 140 mm in all years, with large deficits (> 75 mm) from early June in 1994 and more prolonged large deficits in 1995 and 1996. Restricted water availability first affected canopy expansion at a SMD of 74 mm (50% available water capacity; AW), and canopy senescence at 95 mm (64% AW). Decreases in biomass at harvest were larger with prolonged droughts in 1995 and 1996 (424-562 g/m 2 ) than in 1994 (222 g/m 2 ). Compared in the two driest years, 1995 and 1996, the decrease in biomass was greater in Haven (599 g/m 2 ) than in Maris Huntsman (420 g/m 2 ) (P < 0.05). The better drought resistance of Maris Huntsman appeared to arise through its greater water use efficiency (WUE); 6.2 cf. 5.5-5.7 g/m 2 /mm. The susceptibility of Haven to drought was possibly due to restricted water uptake, depression of radiation use efficiency (RUE) and accelerated senescence. The cultivars differed in flowering by up to 9 days but date of flowering correlated poorly with biomass response to irrigation. Early flowering was, however, correlated with favourable distribution of seasonal water use with respect to the grain filling period. The maximum green area index (GAI) of cultivars varied from 4.4 to 5.3 (P < 0.01), but differences were countered by shifts in the extinction coefficient (K), such that season-long radiation interception varied little. Green area index maxima did not therefore relate to the pattern of growth or water use, and they were correlated poorly with the biomass responses. Cultivars did not differ in their maximum depth of water extraction; they all extracted water to 1.65 m depth in each year. It is concluded that early flowering and high WUE might offer scope for improving drought resistance in the UK's temperate climate, but that small maximum GAI seems less useful.

Responses of potato ( Solanum tuberosum ) to potassium fertilizers

Abstract: Between 1989 and 1999, 33 experiments tested the effects of potassium (K) fertilizer on the yield and quality of potatoes. The experiments were done on a range of soil types and used varieties and management conditions common to modern commercial production. The average yield in these experiments was 48 t/ha. Nearly half of the experiments were done on soils that had exchangeable K values 170-210 kg K/ha. When applied at the optimal rate, the effects of K fertilizer on tuber dry matter concentration were nonsignificant. Exceeding the optimal K application rate caused occasional reductions in tuber dry matter concentrations particularly if potassium chloride (KCl) was used. In the two experiments where it was tested, application rate and form of K had no effect on crisp fry-colour. The effect of K fertilizer on tuber K concentration was measured in 21 experiments and on average each tonne of fresh weight yield was associated with 4.2 kg K. The range in values was large, 2.8-5.7 and related to soil exchangeable K. For fertilizer recommendations based solely on the probability of a significant yield response to K fertilizer it is suggested that no more than 210 kg K/ha be applied even on soils with < 120 mg exchangeable K/l. For fertilizer recommendations based on crop K removal, an uptake value of 4.8 kg K/t fresh weight (FW), as has been suggested, would be adequate, although errors in the estimation of yield may lead to over or under application of K. Since there was little evidence to support fertilizer policies that apply more K than is removed by the crop a fertilizer recommendation system based primarily on the probability of a yield response would be more than sufficient.

The response of dairy cows of high genetic merit to increasing proportion of concentrate in the diet with a high and medium feed value silage

Abstract: Forty-eight high genetic merit Holstein/Friesian dairy cows with Predicted Transmitting Abilities for milk fat plus protein yield, calculated using 1995 as the base year (PTA95 fat plus protein), of 40·0 kg, were used in an eight treatment, two period (period length = 8 weeks) change-over design experiment. Diets were offered ad libitum in the form of a complete diet. Treatments comprised a high and medium feed value silage, with concentrates being incorporated into the diet at proportional inclusion rates of 0·10, 0·30, 0·50 and 0·70 of total dry matter with the high feed value silage, and at 0·32, 0·48, 0·64 and 0·80 of total dry matter with the medium feed value silage. The high feed value silage was produced from a primary regrowth herbage (regrowth interval of 33 days) which was wilted prior to ensiling, while the medium feed value silage was produced from a primary growth herbage harvested on 9 June 1995. The high and medium feed value silages had estimated metabolizable energy concentrations of 12·4 and 11·3 MJ/kg DM respectively. Animals commenced treatments after a mean post calving interval of 26 days.Irrespective of silage feed value, total dry matter intake and milk yield tended to increase with increasing proportion of concentrate in the diet. Milk protein concentrations increased to concentrate inputs of 0·50 and 0·64 of total DM with the high and medium feed value silages respectively, but decreased at the highest concentrate inclusion rates. Milk fat concentrations tended to decrease at higher concentrate inclusion rates. The milk yield responses to increasing proportion of concentrate in the diet have been described by a pair of significantly different equations: Y = 34·2−11·9×0·0101x and Y = 34·2−28·5×0·0101x for the high and medium feed value silages respectively (where Y = milk yield (kg/day) and x = concentrate proportion in the diet on a dry matter basis). Similarly, milk fat and milk protein yields for the two silage types have been described by pairs of significantly different equations. Using these milk yield response equations, it can be calculated that at a concentrate proportion in the diet of 0·32 total dry matter, an additional 3·7 kg of milk per day would be produced by offering the high, rather than the medium feed value silage, while at a concentrate proportion of 0·70 total dry matter, the milk yield benefit associated with the high feed value silage was reduced to 0·6 kg per day. Similarly, total dry matter intakes for animals offered the high feed value silage were 7·4 and 0·8 kg per day greater than for animals offered the medium feed value silage, at concentrate proportions in the diet of 0·32 and 0·70 total dry matter, respectively. These responses indicate that at low concentrate inclusion rates in the diet, silage feed value has a major influence on animal performance, while at higher concentrate inclusion rates, the importance of silage feed value is reduced.

Heterosis, combining ability and genetics for vitamin C, total soluble solids and yield in tomato ( Lycopersicon esculentum ) at 1700 m altitude

Abstract: A study was conducted on a 15 x 15 diallel set of tomato excluding reciprocals to find out the extent of heterosis, combining ability and nature of gene action for yield with two important quality traits: ascorbic acid (vitamin C) and total soluble solids (TSS). Significant differences among genotypes were obtained for all three traits. Positive high significant heterosis was found for yield (41.97, 157.84 and 28.94%), for ascorbic acid (16.68, 54.57 and 161.33%) and for TSS (25.97, 11.93 and 19.02) over the top, the better parent and the commercial control respectively. The magnitude of variance due to general as well as specific combining ability were highly significant indicating the importance of both additive and non-additive gene action. However degree of dominance (o -2 g/o -2 s) revealed the prevalence of a non-additive gene effect. Cross combinations Arka Vikas × Sel-12 (13.19), KS-10 x Pant T-3 (1.66) and EC 818703 x EC 13042 (0.88) were best specific combiners for ascorbic acid, total soluble solids and yield/plant. Predominance of non-additive gene action plays a greater role in the inheritance of ascorbic acid and total soluble solids in tomato under hill conditions.

Integrated nutrient management by using farmyard manure and fertilizers in potato–sunflower–paddy rice rotation in the Punjab

Abstract: A rotation experiment was conducted on an alluvial soil at Central Potato Research Station, Jalandhar, India between 1994 and 1999 to develop an integrated nutrient management programme for a potato–sunflower–paddy rice rotation. It tested 10 fertilizer treatments that combined application of 50, 100 and 150% of the recommended rates of inorganic nitrogen (N), phosphorus (P) and potassium (K) with farmyard manure (FYM) and in some cases zinc. Potatoes were the most nutrient-responsive crop followed by paddy rice and sunflower. The responses of potatoes to both P and K were greater in frost and late blight years. In these experiments potatoes required NPK at 150% of the currently recommended rate for maximum tuber production (i.e. they required 270 kg N, 52 kg P and 150 kg K/ha). Application of FYM at 30 t/ha with 270 kg of inorganic N/ha (FYM+N) was less effective than the use of NPK at 150% of the currently recommended rate. Application of K to replace that removed in the harvested crop was more effective in potatoes than giving K at 100 or 150% of the currently recommended rate.Sunflowers grown after potatoes that had received NPK at 150% of the currently recommended rate or with the FYM+N treatment required only half of the currently recommended rate of NPK for maximum yield (i.e. they required 23 kg N, 7 kg P and 13 kg K/ha), whereas paddy rice, grown as a third crop, required the full amount of NPK at the currently recommended rate (i.e. 120 kg N, 26 kg P and 67 kg K/ha). Application of K to adjust for its removal did not benefit sunflowers or paddy rice. Zinc had no direct effect on potatoes or any residual effects on the succeeding sunflower and paddy rice crops. The effects of the FYM+N treatment were cumulative, especially on potatoes which were the most responsive crop, whereas those involving the application of NPK at 150% of the currently recommended rate were not. Also, the NPK fertility of the soil was enhanced and more organic carbon was present following the FYM+N treatment than with NPK fertilizers applied at the currently recommended rate. Application of P resulted in a build-up of P but none of the treatments, even the applications of K to adjust for its removal, maintained the K status of the soil at its initial level.

The effect of water stress on grain filling processes in wheat

Abstract: The effect of water stress, commencing from the late cell division period, on in vivo grain growth was studied in relation to grain sucrose, water status and in vitro starch synthesis. Detached ear experiments were conducted to assess the effect of sink dehydration on grain filling processes under non-limiting source conditions. Water stress caused premature grain desiccation and resulted in a marked decline in grain sucrose and reduced grain weight. Both sucrose uptake and conversion to starch in vitro were increased by mild water stress (solute potential (Ψ s )-0.8 MPa). However, a decline in Ψ s below this optimum resulted in reduced sucrose uptake and starch synthesis not attributable to a reduced supply of sucrose. Stressed grains which failed to accumulate dry matter in vivo showed significant starch synthesis when cultured in vitro. Grains from in situ and osmotically stressed plants showed a lower capacity for starch synthesis in vitro. The results indicate that grain filling processes under stress conditions are limited by (1) low substrate availability and low Ψ s within the sink i.e. an unfavourable seed environment (non-lasting effect) and (2) reduced synthetic capacity of the sink (carry-over effect).

Mansfeld's Encyclopedia of Agricultural and Horticultural Crops, ed P. HANELT. 3645 pp. Berlin: Springer-Verlag Publishers (2001). £614.00, US $899.00 (hardback). ISBN 3 540 41017 1.

Abstract: This excellent edited volume on the uptake and metabolism of nitrogen in plants is, according to the preface, an outcome of the increased use of nitrogenous fertilizers in increasing agricultural production and the resulting environmental hazard of nitrate, with crop plant growth and metabolism as major components of these changes to the nitrogen cycle. The focus of the book is on what happens between nitrogen fertilization and ‘excess ’ nitrogen, i.e. on the extent and mechanism of uptake of soil (including fertilizer) nitrogen, and the means by which the nitrogen is transported, transformed and stored within the plant and is used in plant growth, ending with a discussion of combined nitrogen in the environment. The editors ’ introduction puts the uptake and metabolism of nitrogen in plants into its agronomic and environmental context, and emphasizes the role of recent advances in molecular biology, and new techniques, understanding and modelling in biochemistry and physiology of the nitrogen relations of plants, in increasing our knowledge of how nitrogen behaves in plants. This introduction is followed by the eight chapters, six of which have two (in one case, three) components, each written by two or more authors. These up to date and clearly written reviews deal with Nitrate Assimilation, Ammonia Assimilation, Symbiotic Nitrogen Fixation, Nitrogen and Seed Storage Proteins, Nitrogen andYield, andNitrogen in theEnvironment. While some of these chapter titles are rather opaque (e.g. ‘Nitrogen Traffic’) the content is better explained in the titles of the (in this case) two components of the chapter. As might be expected from the co-publication of this volume by Springer-Verlag and Editions INRA many of the authors are from France, and most of the rest are from other European countries, with two from the United States and one from Australia. The literature coverage is, nevertheless, worldwide, although there is an emphasis on European examples in discussing the environmental impacts of human intervention in the nitrogen cycle. The literature surveyed was mainly published in 1999 or earlier, with a few references to work published in 2000. This book is attractively produced and has a good index and few typographical errors. It provides a critical account of the role of plants in the nitrogen cycle, relating agronomic and environmental aspects to molecular genetic, biochemical and physiological aspects. While not focusing entirely on topics which are central to readers of the Journal of Agricultural Science, it is certainly a volume to which they should have access. . . 

Dynamics of nitrogen capture without fertilizer: the baseline for fertilizing winter wheat in the UK

Abstract: Experiments at three sites in 1993, six sites in 1994 and eight sites in 1995, mostly after oilseed rape, tested effects of previous fertilizer N (differing by 200 kg/ha for 1993 and 1994 and 300 kg/ha for 1995) and date of sowing (differing by about 2 months) on soil mineral N and N uptake by winter wheat cv. Mercia which received no fertilizer N. Soil mineral N to 90 cm plus crop N (‘soil N supply’; SNS) in February was 103 and 76 kg/ha after large and small amounts of previous fertilizer N respectively but was not affected by date of sowing. Previous fertilizer N seldom affected crop N in spring because sowing was too late for N capture during autumn, but it did affect soil mineral N, particularly in the 60–90 cm soil horizon, presumably due to over-winter leaching. Tillering generally occurred in spring, and was delayed but not diminished by later sowing. Previous fertilizer N increased shoot survival more than it increased shoot production. Final shoot number was affected by previous fertilizer N, but not by date of sowing. Overall, there were 29 surviving tillers/g SNS.N uptakes at fortnightly intervals from spring to harvest at two core sites were described well by linear rates. The difference between sowings in the fitted date with 10 kg/ha crop N was 1 month; these dates were not significantly affected by previous fertilizer. N uptake rates were increased by both previous fertilizer N and late sowing. Rates of N uptake related closely to soil mineral N in February such that ‘equivalent recovery’ was achieved in late May or early June. At one site there was evidence that most of the residue from previous fertilizer N had moved below 90 cm by February, but N uptake was nevertheless increased. Two further ‘satellite’ sites behaved similarly. Thus at 14 out of 17 sites, N uptake until harvest related directly and with approximate parity to soil mineral N in February (R2 = 0·79), a significant intercept being in keeping with an atmospheric contribution of 20–40 kg/ha N at all sites.It is concluded that, on retentive soils in the UK, SNS in early spring was a good indicator of N availability throughout growth of unfertilized wheat, because the N residues arising from previous fertilizer mineralized before analysis, yet remained largely within root range. The steady rates of soil mineral N recovery were taken as being dependent on progressively deeper root development. Thus, even if soil mineral N equated with a crop's N requirement, fresh fertilizer applications might be needed before ‘equivalent recovery’ of soil N, to encourage the earlier processes of tiller production and canopy expansion. The later process of grain filling was sustained by continued N uptake (mean 41 kg/ha) coming apparently from N leached to the subsoil (relating to previous fertilizer use) as well as from sources not related to previous fertilizer use; significant net mineralization was apparent in some subsoils.

Variation in outcrossing levels in faba bean cultivars: role of ecological factors

Abstract: Understanding the role of pollinators in determining the outcrossing rate is very important for the development of synthetic varieties of faba bean. Isozyme markers have been used to study the multilocus outcrossing rate in five cultivars under field conditions and in two locations. The study was carried out at Cordoba (Spain) and at Rennes (France). These two locations were chosen because previously studies showed strong differences in cross-pollination. Multilocus outcrossing rates at both locations, Cordoba and Rennes, were 0.65 and 0.33 respectively. Local differences in pollinator abundance and foraging activity were 26 and 32 times higher, respectively, at Cordoba than at Rennes which could explain an outcrossing rate twice at Cordoba compared with Rennes. So, pollinators may play a prominent role in determining the differences in outcrossing between locations. However, at a local level, there is a highly significant positive correlation between foraging activity and outcrossing only at Rennes (where the number of pollinators is scarce) but not at Cordoba (where pollinators are abundant). We suggest that although pollinators have a major impact on the level of outcrossing, in circumstances where there are a lot of pollinators the differences in outcrossing between cultivars depends on other factors among which is the ability of the genotype itself to outcross. No type of floral display seems to be clearly important in the determination of the outcrossing level in such a case. The implication of our results for faba bean breeding strategies is discussed.

Comparative effectiveness of phosphate-enriched compost and single superphosphate on yield, uptake of nutrients and soil quality under soybean–wheat rotation

Abstract: Low organic matter concentration coupled with low native soil phosphorus (P) concentrations is a major constraint limiting the productivity of a soybean-wheat system on Vertisols in the Indian semi-arid tropics. In a 3-year field study (1996-99), the performance of four different composts obtained from legume straw (Glycine max Merr.L), cereal straw (Triticum aestivum), oilseed straw (Brassica juncea L.) and city rubbish were compared, and also with chemical fertilizers in terms of degree of maturity, quality of compost, improvement in soil organic matter, biological activities of soil and yields of soybean and wheat. Phospho-sulpho-nitrocomposts (phosphocomposts) were prepared containing approximately 2.5 to 4.2 % P and 1.4 to 2.3 % N, in an aerobic decomposition process for 4 months by adding an aqueous slurry of 1:1 (dry weight) cow dung, 2.2% P in the form of low grade Mussorie phosphate rock (7.5 % P), 10 % pyrite (S, 22.2 %) and 0.5% urea N, and bioinoculums such as the cellulose decomposers Paecilomyces fusisporus and Aspergillus awamori, and P-solubilizing organisms i.e. Bacillus polymyxa and Pseudomonas striata. The maturity indexes were strongly associated with the source of materials, chemical composition and degree of decomposition. The matured composts had lower C/N ratios (8.2 to 21.7) and water soluble carbohydrates (0.23 to 0.43%) and larger ratios of cation exchange capacity/total organic carbon (CEC/TOC) and lignin/cellulose than the initial. The matured compost increased total P, water soluble P, citrate soluble P, total N and NO 3 -N and the application of phosphocompost at the rate of 10 t/ha gave plant growth dry matter accumulation, seed yield and P uptake by soybean equivalent to single superphosphate at 26.2 kg P/ha. The continuous turnover of enriched phosphocompost increased soil microbial biomass C and the activity of enzymes compared to application of chemical fertilizer.

Evaluation of six chickpea varieties for seed yield under autumn and spring sowing

Abstract: The possibility of increasing seed yield in chickpeas was studied by changing sowing time from spring to autumn in an experiment conducted in central Greece over 4 years. Six chickpea varieties, two susceptible to Ascochyta blight and Sclerotinia diseases and four resistant, were evaluated in two sowing seasons (autumn and spring).Results showed that autumn sowing in comparison with spring influenced reproductive and growth periods of the varieties as follows: advanced initiation of flowering (April instead of May), increased flowering duration of the varieties from 7 to 13 days and advanced time for harvest, on average up to 4 days when an exceptionally rainy spring prevailed and up to 30 days when exceptionally dry. Due to the above changes induced by autumn sowing, varieties yielded on average from 23–188% (655–1015 kg/ha) more than if they were sown in spring. The largest per cent increase was observed during the year with the driest spring and the smallest during the year with the wettest spring. The two susceptible varieties ‘Thiva’ and ‘Gravia’ when infected by Ascochyta blight and Sclerotinia diseases in autumn sowing, had yields similar to the spring sowing. However, during the years without infection these two varieties yielded more in autumn sowing.

Assessment of the CERES-Rice model for rice production in the Central Plain of Thailand

Abstract: CERES-Rice model was used to simulate growth and yield of four common rice varieties in Thailand with the attention on rate and timing of N application, a factor that most limits crop yield. The model predicted slightly higher grain yield than that observed for all varieties at N input of 75 kg/ha, but the differences between observed and simulated yields were not significant, except for varieties HSP and SPR90. The simulated grain[ratio ]straw ratio was significantly higher than the observed value for all varieties except that of HSP. There was no significant difference between the simulated and observed values of days to flowering. Generally, the model reasonably predicted the phenology and yields of RD23 and KDML105 varieties. The model was also used to compare the yields of KDML105 variety as influenced by rate and timing of N application grown in acid sulphate soils. There was a variation in predicted biomass yield with applied N rates at 0 and 150 kg/ha, but timing of application had no effect. In Aeric Endoquept and Sulfic Tropaquept soils at Suphan Buri and Pathum Thani rice research stations, the yield patterns remained unchanged and showed a positive response to N rate up to 75 kg/ha. The model estimated higher grain yields beyond 75 kg N/ha while the observed yield decreased. Based on the simulated yields for a 10-year period at the Asian Institute of Technology (AIT), Pathum Thani, Suphan Buri, Nakhon Pathom and Ratcha Buri rice research stations the varieties were ranked as: SPR90 > RD23 = HSP > KDML105. The model suggested that SPR90 is the most suitable variety for the central plain and its potential yield ranges from 4030 to 5600 kg/ha. Pathum Thani province, with acid sulphate soils, had the lowest potential for rice production.

Effects of 15N-labelled crop residues and management practices on subsequent winter wheat yields, nitrogen benefits and recovery under field conditions

Abstract: SUMMARY Nitrogen-15 enriched ammonium sulphate was applied to micro-plots in a field in which two leguminous (white clover and peas) and two non-leguminous (ryegrass and winter wheat) crops were grown to produce "&N-labelled crop residues and roots during 1993}94. Nitrogen benefits and recovery of crop residue-N, root-N and residual fertilizer-N by three succeeding winter wheat crops were studied. Each crop residue was subjected to four dierent residue management treatments (ploughed, rotary hoed, mulched or burned) before the first sequential wheat crop (1994}95) was sown, followed by the second (1995}96) and third wheat crops (1996}97), in each of which residues of the previous wheat crop were removed and all plots were ploughed uniformly before sowing. Grain yields of the first sequential wheat crop followed the order: white clover " peas " ryegrass " wheat. The mulched treatment produced significantly lower grain yield than those of other treatments. In the first sequential wheat crop, leguminous and non-leguminous residues supplied between 29‐57% and 6‐10% of wheat N accumulated respectively and these decreased with successive sequential crops. Rotary hoed treatment reduced N benefits of white clover residue-N while no significant dierences in N benefits occurred between residue management treatments in non-leguminous residues. On average, the first wheat crop recovered between 29‐37% of leguminous and 11‐13% of nonleguminous crop residues-N. Corresponding values for root plus residual fertilizer-N were between 5‐19% and 2‐3%, respectively. Management treatments produced similar eects to those of N benefits. On average, between 5 to 8% of crop residue-N plus root and residual fertilizer-N was recovered by each of the second and third sequential wheat crops from leguminous residues compared to 2 to 4% from non-leguminous residues. The N recoveries tended to be higher under mulched treatments especially under leguminous than non-leguminous residues for the second sequential wheat crop but were variable for the third sequential wheat crop. Relatively higher proportions of leguminous residue-N were unaccounted in ploughed and rotary hoed treatments compared with those of mulched and burned treatments. In non-leguminous residue-N, higher unaccounted residueN occurred under burned (33‐44%) compared with other treatments (20‐27%).

Adjusting for fertility and competition in variety trials

Abstract: A joint model for plot yield in response to fertility trends and interplot competition is described. The model combines the mixed model representation of a cubic smoothing spline to model fertility and a regression model with auto-regressive terms to model competition. Estimation is based on a generalization of residual maximum likelihood. The methods were applied to a series of 70 sugar beet trials conducted by the Plant Breeding Institute, Cambridge, UK, and the results summarized.

Evaluation of groundnut genotypes for heat tolerance under field conditions in a Sahelian environment using a simple physiological model for yield

Abstract: Heat tolerance of groundnut (Arachis hypogaea L.) was evaluated under field conditions using physiological traits identified in a yield model [crop growth rate (C), reproductive duration (Dr) and partitioning (p)]. In 1991, 625 diverse genotypes were initially screened under irrigation during the hottest months (February to May). Subsequent tests consisted of 16 contrasting genotypes selected based on a combination of high pod yield and partitioning coefficient of >0· 50. Large variation was observed among the 625 genotypes for pod yield and physiological traits. C was a powerful factor influencing pod yield. Eight genotypes combining high pod yield and a partitioning coefficient greater than 0·6 were identified. These included two released cultivars (55–437 and 796) in the Sahel. Correlations between seasons were significant for p (r=0·84), but non-significant for pod yield (r=0·40), C (r=0·39), and Dr (0·36). Date of sowing and genotypes had significant effects on pod yield and C, but were slight on p and Dr. Pod yield of most genotypes declined by more than 50% when flowering and pod formation occurred when maximum temperatures averaged 40°C. The results revealed that estimates of p would be a more reliable selection criterion for identification of genotypes tolerant to heat than yield. Further research is suggested to maximize crop growth rate and partitioning of genotypes growing under supra-optimal temperatures.

Optimum plant populations for okra ( Abelmoschus esculentus ) in a mixture with cassava ( Manihot esculenta ) and its relevance to rainy season-based cropping systems in south-western Nigeria

Abstract: Experiments were conducted in Nigeria to evaluate the optimum plant population density for okra (Abelmoschus esculentus) sown in monoculture or intercropped with cassava (Manihot esculenta). The crops were sown as late and early season crops in 1997 and 1998. Okra was sown at varied spacings to achieve final plant densities of 25000, 35000 and 50000 plants/ha in both monoculture and mixed stands. Intercropping had no significant effect on okra phenology (time to vegetative growth, flowering and fruiting). However, it significantly reduced weed growth by 25–45% and nematode infection in okra by 36%, and kept the canopy environment of cassava cooler by 3·0–4·4°C and more moist by 5–10g/kg, compared with monoculture. The durations of vegetative and reproductive growth and the weed-control ability of okra in both cropping systems were influenced by population density. Okra sown at 50000 plants/ha took the longest time to reach specific phenological stages, controlled weeds best and gave the highest fresh pod yields in both seasons. There was little increase in pod yields between 35000 and 50000 plants/ha in mixed stands in late season sown crops. The growth and tuber yield of cassava were not significantly affected by intercropping and okra population density.The growth of okra and cassava were better with early than late season sowing, irrespective of okra population density or cropping system. This appears to have been due mainly to the effect of temperature and rainfall differences between the seasons. The substantial variation in the weather during the two seasons also had greater effect in monoculture than mixed stands. It is concluded that when rainfall is limiting, okra could be intercropped with cassava using population density up to 35000 plants/ha to allow the vegetable to develop and to maximize pod yield under the relatively dry conditions. The optimum target suggested is 50000–60000 plants/ha during the wet periods.

Effect of genotype of Trifolium repens on mycorrhizal symbiosis with Glomus mosseae

Abstract: Forty-three near-isogenic lines (NILs) of white clover (Trifolium repens), derived from four parental self-compatible genotypes containing the rare self-fertility allele, were inoculated with the arbuscular mycorrhizal fungus Glomus mossae. Plant growth response (shoot and root weight and root length), shoot P uptake and mycorrhizal root infection rates were recorded 12 weeks after inoculation. There was generally a high degree of variation between individual lines in all recorded parameters. The most sensitive indicator of plant response to mycorrhizal infection was root length with almost half of all lines showing significant responses (in most cases a decrease in root length). Shoot weight was significantly different between mycorrhizal and nonmycorrhizal plants in nine lines. Parental genotype significantly affected both plant response to mycorrhiza as well as mycorrhizal infection rates. The results suggest that the NILs will prove useful for further studies to elucidate the molecular genetic control of the symbiosis and inform plant breeding strategies of this agronomically important species.

The use of radiation interception and transpiration to predict the yield of healthy, droughted and virus-infected sugar beet.

Abstract: This paper reports an analysis of the yield of sugar beet crops grown under experimental conditions between 1993 and 1995 in the UK. Crops were either healthy (unstressed) or subjected to drought, infection with Beet yellows virus (BYV) or a combination of both. The study investigated whether the large differences in yield between the crops grown in different seasons and subjected to different stresses could be accounted for by simple relationships between total biomass and radiation interception (e s ), transpiration (e w ) or e s and e w adjusted for mean saturation deficit (Ω s and Ω w respectively). Mean values of e s , e w , Ω s and Ω w in healthy crops were 1.42 g/MJ, 0.89 g/kg, 6.76 g/kPa/MJ and 4.29 g/kPa/kg respectively. Variations in the dry matter yield between seasons were best accounted for by Ω u and less well by e u or e s . Ω s accounted for least variation in yield between seasons. None of these relationships remained constant in stressed plants; both drought and BYV-infection decreased e s (and Ω s ) but Ω u was increased by drought and decreased by BYV-infection. However, in common with healthy crops, seasonal variation in yields was best accounted for by Ω w . Mean values of e s , Ω s , e w and Ω w for all healthy, infected and droughted crops accounted for 61, 50, 88 and 97% of the variation in dry matter yield between experiments respectively. Accurate prediction of the yield of stressed plants requires a knowledge of their infection and drought status. If this information is unavailable then the mean value of Ω w for healthy, infected and droughted crops will provide a reasonable prediction of the yield of such crops.

Comparison of fertilizer strategies for reducing nitrate leaching from grazed grassland, with particular reference to the contribution from urine patches

Abstract: The effectiveness of alternative fertilizer strategies to control nitrate leaching was investigated in a field experiment at IGER, Aberystwyth using simulated pastures to represent swards grazed by dairy cattle between May and October 1997, following an initial silage cut Cut-plots with and without applications of artificial urine were used to represent the separate components of grazed pastures managed with the following nitrogen (N) fertilizer strategies: standard (fertilizer applied uniformly to all areas of the sward at a total rate of 180 kg N/ha between May and October), tactical (fertilizer rates adjusted to match the average soil mineral-N content of the pasture to that of ungrazed reference plots receiving the standard rate) and patch-avoidance (fertilizer applied at the standard rate but withheld from areas that had received urine) Calculated stocking rates derived from herbage yields indicated that 12 % of the pasture would have been affected by urine up to the end of grazing' in October The presence of urine patches increased the nitrate-N content of the 0-90 cm soil profile in October from 61 kg N/ha for ungrazed pasture to 104 kg/ha for grazed' pasture receiving the standard fertilizer rate Although the patch-avoidance strategy was more effective than the tactical in reducing the accumulation of nitrate in soil under urine patches, they were both of limited effectiveness in reducing the content over the pasture as a whole Profile contents in October for the simulated pastures managed with the tactical and patch-avoidance strategies were equivalent to 99 and 97 kg nitrate-N/ha, respectively The tactical strategy achieved a 26 % saving in overall fertilizer use Under the conditions of the experiment this did not significantly reduce herbage yields The patch-avoidance strategy reduced fertilizer use by only 3%

Effects of soil- and foliar-applied phosphorus fertilizers on the potato ( Solanum tuberosum ) crop

Abstract: Twenty-two field experiments in England, done between 1986 and 2000, tested the effects of phosphorus (P) fertilizers on number of tubers and tuber yield in Solanum tuberosum. Applying P fertilizer resulted in statistically significant increases in tuber yield in six experiments and the optimal P application rate ranged from c. 90 to 180 kg P/ha. Statistically significant increases in yield in response to application of P fertilizers were found only in soils that contained 26 mg/l. The absence of yield responses on P Index 3 soils found in the current experiments was attributed to increased use of irrigation that may have increased the availability of soil P. Re-interpretation of data from long-term experiments showed that the agronomic benefits of increasing soil P status by applying more P than is removed by harvested crop parts, are small. Since large P residues, estimated by Olsen-P or degree of soil P saturation, are associated with desorption of P and consequent loss to drainage water it is inadvisable to increase soil P above Index 3. For these reasons, no P fertilizer is recommended for Index 4 soils, an amount equivalent to replacement is recommended for Index 3 soils but up to 110–130 kg P/ha should be applied to Index 0 soils. Applications of foliar P had no effect on number of tubers or tuber yield and this practice cannot be recommended.

The impact of modern farming practices on soil fertility and quality in England and Wales

Abstract: Data are presented on the effects of modern farming practices on soil as an agricultural resource in England and Wales (E&W), namely: nutrient status, pH, soil organic carbon (SOC), heavy metal concentrations, and on soil erosion risk. Fertilizer-N inputs to tillage (arable) and grassland soils increased from 84 and 65 kg/ha N in 1969 to 151 and 120 kg/ha N, respectively, in 1997. The estimated N surplus (inputs less outputs) increased from 84 and 96 kg/ha N to 102 and 154 kg/ha N, respectively, over the same time. Phosphorus inputs to tillage (mean 37 kg/ha P) and grassland (mean 21 kg/ha P) changed little over the period. However, P surpluses decreased from 25 kg/ha P in 1969 to 15 kg/ha P in 1997 on tillage land (largely as a result of greater P offtakes), and from 20 to 17 kg/ha P in 1997 on grassland (largely because of a small decrease in fertilizer P). The cumulative tillage land soil P surplus was c. 580 kg/ha P, and was estimated to increase topsoil total P concentrations by c. 170 mg/kg P and Olsen-extractable soil P by c. 26 mg/l P. The mean annual P surplus for grassland was 18 kg/ha P which, over the study period, added c. 427 kg/ha P to the soil, an increase in topsoil total P of c. 214 mg/kg P, and in Olsen-extractable P of 19 mg/l P.Concentrations of SOC in some soils have decreased between 1980 and 1995, especially where soils have been ploughed out of grassland and on lowland organic and peaty soils in tillage. The mean SOC of soils in arable/ley cultivation in 1980 was 3·4% and 2·8% in 1995.The proportion of arable soils with pH < 6·0 decreased from 10% in 1969–73 to 4% in 1990–93, reflecting the better targeting of lime inputs. In contrast, the proportion of grassland soils with pH < 6·0 increased from 39% in 1969–73 to 56% in 1990–93.Although there were statistically significant changes in the mean soil concentrations of Cd, Cu, Ni, Pb and Zn between 1980 and 1995, many of the changes were small in absolute terms. Hence, there was little evidence of marked or systematic changes in topsoil total heavy metal concentrations that could not be explained by factors other than increased pollutant loadings.Over the next 50 years or so, the threat from soil erosion to crop productivity will be greatest on shallow soils ([les ] c. 0·3 m depth), mostly over chalk and sandstone as further removal of soil will lead to increased drought stress. Provided that nutrient supplies are maintained, the evidence is that losses in arable crops on eroded soils would range between 2% and 8% of current yields.Thus, within the limitations of the data available, both in time and space, we found little evidence that most soils in E&W cannot continue to support modern farming practices, and the associated crop and animal outputs, given appropriate inputs of nutrients and an adequate degree of crop protection.