Showing papers by "Guangdi Li published in 2015"

Grass-legume mixtures impact soil N, species recruitment, and productivity in temperate steppe grassland

Abstract: In this study, we aimed to understand effects and mechanisms of legume species and their relative abundance on soil N, species recruitment, and productivity in mixed grassland. We also assessed the utilization prospect of several legumes in natural grassland. In 2006, grass-legume combinations (GLCs) with different ratios (GLR) were established using Leymus chinensis and four legume species (Medicago ruthenica, Lespedeza daurica, Medicago falcata, and Medicago sativa). In 2009, plant and soil samples were taken to examine the differences in soil nitrogen (N) properties, biological N fixation (BNF), recruitment characteristics, and aboveground biomass of the community under different mixture patterns. Soil total N and available N concentration increased when legume component increased from GLR 1:0 (grass monoculture) to GLR 1:1 (grass:legume 1:1) but decreased as legume component increased further from GLR 1:3 (grass:legume 1:3) to GLR 0:1 (legume monoculture). GLR 1:1 had the highest BNF in most GLCs except for L. chinensis-M. falcata. For any GLR with legume, L. chinensis-M. sativa combination (L-MS) had higher soil total N, available N, water content, and BNF. The legume combinations with a GLR lower than 1:1 resulted in more species recruitments compared with the grass monoculture, and L-MS induced relatively more species recruitments than other GLCs, which were correlated with improved soil water and NO3 −-N status. The grassland productivity increased as the GLR decreased; in any GLRs with legume, higher productivity was found under L-MS combination, and current results showed that grassland productivity was positively linked to soil NO3 −-N availability influenced by grass-legume mixture. We concluded that the species and relative abundance of legumes had great impact on soil N status, species recruitment, and productivity in this temperate grassland ecosystem. In this study site, legume introduction can be considered as an alternative to N fertilization for increasing grassland productivity. M. sativa has the greatest economic and ecological potential species to be mixed into natural temperate steppe grassland, and grass-legume ratio 1:1 is the best combination in mixed communities.

Impact of Climate Change on Temperate and Alpine Grasslands in China during 1982–2006

Abstract: Based on GIMMS NDVI and climate data from 1982 to 2006, this study analyzed the impact of climate change on grassland in China. During the growing season, there were significant effects of precipitation on the growth of all the grassland types ( ), except for meadow vegetation. For the air temperatures, there existed asymmetrical effects of maximum temperature ( ) and minimum temperature ( ) on grassland vegetation, especially for the temperate grasslands and alpine steppe. The growing season NDVI correlated negatively with but positively with for temperate grasslands. Seasonally, these opposite effects were only observed in summer. For alpine steppe, the growing season NDVI correlated positively with but negatively with , and this pattern of asymmetrical responses was only obvious in spring and autumn. Under the background of global asymmetric warming, more attention should be paid to this asymmetric response of grassland vegetation to daytime and night-time warming, especially when we want to predict the productivity of China’s grasslands in the future.

A Framework for Modelling Whole-Farm Financial Risk (PowerPoint)

Abstract: We consider the limitations of optimisation analyses that ignore farm-level financial risks arising from combinations of high fixed costs, including debt burdens and highly variable local weather and prices. A sequential multivariate analysis method is used to compute cumulative distribution functions of decadal whole-farm cash balances for a farm facing highly variable prices and weather, and a level of opening debt. This enables direct probabilistic projections of long-term whole-farm financial viability typical of the Coolamon area in New South Wales. We contrast this with a partial-budgeting linear programming study using average annual prices and weather for the same farm. Our focus is on the effects of varying sheep stocking rates, given different pasture compositions in rotation with cropping under weather and price variations over time and different levels of starting debt. We show how best practice recommendations based on partial costing might mislead by ignoring the powerful cumulative effects of input variability and compounding debts. Increasing production, often already near the achievable water-limited potential, can be of far lower priority than reducing costs and lowering heavy debt burdens. We demonstrate that whole-farm financial risk profiles of a farm’s options provide a richer, more meaningful basis for sound advice.

Morphological and structural plasticity of grassland species in response to a gradient in saline-sodic soils.

Abstract: The abundance and distribution of species can be ascribed to both environmental heterogeneity and stress tolerance, with the latter measure sometimes associated with phenotypic plasticity. Although phenotypic plasticity varies predictably in response to common forms of stress, we lack a mechanistic understanding of the response of species to high saline-sodic soils. We compared the phenotypic plasticity of three pairs of high and low saline-sodic tolerant congeners from the families Poaceae (Leymus chinensis versus L. secalinus), Fabaceae (Lespedeza davurica versus L. bicolor) and Asteraceae (Artemisia mongolica versus A. sieversiana) in a controlled pot experiment in the Songnen grassland, China. The low tolerant species, L. secalinus and A. sieversiana exhibited higher plasticity in response to soil salinity and sodicity than their paired congeners. Highly tolerant species, L. chinensis and A. mongolica, had higher values for several important morphological traits, such as shoot length and total biomass under the high saline-sodic soil treatment than their paired congeners. In contrast, congeners from the family Fabaceae, L. davurica and L. bicolor, did not exhibit significantly different plasticity in response to soil salinity and sodicity. All species held a constant reproductive effort in response to saline-sodic soil stress. The different responses between low and high tolerant species offer an explanation for the distribution patterns of these species in the Songnen grassland. Highly tolerant species showed less morphological plasticity over a range of saline-sodic conditions than their paired congeners, which may manifest as an inability to compete with co-occurring species in locations where saline-sodic soils are absent.

Changed recommendations for the use of phalaris on acid soils

Abstract: Phalaris (Phalaris aquatica L.) has been cultivated in Australia as a forage grass for over a century. Since the 1970’s it has developed a reputation for being sensitive to soil acidity with conventional wisdom typically advising against its use on acid soils. However, several recent studies have called this view into question and have prompted a revision of the recommendations for the use of phalaris on acid soils. The release of new phalaris cultivars, first with cv. Landmaster in 1996 and later cv. Advanced AT in 2008, which have demonstrated superior tolerance to aluminium (Al) toxicity needs to be acknowledged. Yet, even prior to these developments it was evident that phalaris performance on acidic soils far exceeded contemporary expectations. We now have documented evidence of phalaris persisting in the field beyond pH and Al thresholds at which it is deemed suitable, and of phalaris persisting significantly better in strongly acid soils than species perceived to be highly tolerant of acidity, such as cocksfoot (Dactylis glomerata L.). Indeed, phalaris is endemic in many acid soil environments across the Tablelands of south-eastern Australia. It is suggested that phalaris should be considered for inclusion in new plantings on acid soils not only for its acid tolerance, but also for its drought tolerance which increases the resilience of pasture swards. Of course, any new plantings of phalaris in strongly acid soil environments should always use more tolerant cultivars following lime application. However, being a deep-rooted species, phalaris requires adequate soil nutrition and depth, and is less well suited to shallower soils which may also be acidic.

Using broadleaf crops to improve wheat grain yield and on farm profitability

Abstract: Broadleaf species are included in cropping systems to improve soil nitrogen (N) fertility, manage difficult weeds and reduce cereal disease incidence in crop rotations. A 4-year crop sequence experiment was conducted at Wagga Wagga to quantify the yield benefit of break crops (canola, field pea, lupin, vetch and high density legume pasture) to wheat crops in subsequent years. Results showed that grain yield increased significantly for the first wheat crop following any break crop that was brown manured. The benefit of break crops diminished in the 2nd and 3rd wheat crops although the grain yields tended to be higher under brown manured treatment. The yield benefits to subsequent wheat crops derived from legumes were compromised when harvested for grain or cut for hay. Overall, the N benefit from legumes was greater than, or equivalent to, fertiliser N (75 kg N/ha) for at least two wheat crops after break crops. Averaged across 4 years, the rotation with canola had the highest gross margin (average $500/year), and treatments that were brown manured were the lowest (average $259 - $289/year) due to income loss in year 1. The brown manured treatments, however, offer opportunities to manage herbicide resistant weeds and reduce the risk of diseases and provide significant N benefits.

Sirolan phalaris and Kasbah cocksfoot prove more persistent than lucerne under drought in a medium rainfall cropping environment

Abstract: Cultivars of phalaris (Phalaris aquatica L.) and cocksfoot (Dactylis glomerata L.) suited to lower rainfall cropping environments have existed in Australia for over 40 years, but remain rarely used in commercial crop rotations. A field experiment was established in 2010 at Ariah Park, NSW, to test the persistence of phalaris cv. Sirolan and cocksfoot cv. Kasbah compared to winter active and semi-winter dormant lucerne (Medicago sativa L.) cultivars on a red soil where the average annual rainfall is 460 mm. All treatments established successfully in 2010 and persisted well through the summers of 2010/11 and 2011/12 which were both substantially wetter than average. A rapid reduction in perennial plant density was observed in all treatments following the dry spring/summer period of 2012/13. However, the basal frequency of Sirolan phalaris (19%) and Kasbah cocksfoot (25%) was greater than either winter active or semi-winter dormant lucerne genotypes (4-5%). Sirolan was the most productive of all perennial treatments, producing significantly more dry matter than lucerne in years 1, 4 and 5. Kasbah cocksfoot was more productive than lucerne in year 5 only, but was significantly less productive in year 2. This study showed that the perennial grasses were productive and persistent in this environment and their greater use could benefit modern crop rotations.

Alternate row sowing: a novel approach to maintain sown species in mixed pasture swards

Abstract: Establishing and maintaining a balanced mixture of perennial and annual pasture species is often difficult, especially in drier environments. One method to reduce the competition between pasture species and to improve the potential productivity and nitrogen fixed by the pasture is to establish pasture species in separate rows (alternate row sowings). An experimental field site was established in the autumn of 2012 near Mirrool in southern NSW. Medicago sativa and Phalaris aquatica were sown in combination with a range of annual legumes either as a monoculture, mixture, or arranged in alternate rows in 1:1 or 1:2 ratios. Legumes were inoculated with appropriate rhizobia and the sites were fertilised with Starter 15 at 150 kg/ ha. Seedling establishment, regeneration and dry matter (DM) were measured each year until 2014. Annual legume seed reserves and nitrogen fixation (N-fix) were measured in 2013. Alternate row sowing improved seedling regeneration and annual legume seed reserves in some situations; however, it did not significantly improve mean DM, mean legume DM or N-fix. In contrast the choice of species combinations impacted on these responses. For example, the inclusion of P. aquatica in the pasture mix tended to increase mean DM, although if N-fix and mean legume DM were to be maintained at acceptable levels, M. sativa and Trifolium subterraneum were important inclusions in combination with P. aquatica.

A Framework for Modelling Whole-Farm Financial Risk

Abstract: We consider the limitations of optimisation analyses that ignore farm-level financial risks arising from combinations of high fixed costs, including debt burdens and highly variable local weather and prices. A sequential multivariate analysis method is used to compute cumulative distribution functions of decadal whole-farm cash balances for a farm facing highly variable prices and weather, and a level of opening debt. This enables direct probabilistic projections of long-term whole-farm financial viability typical of the Coolamon area in New South Wales. We contrast this with a partial-budgeting linear programming study using average annual prices and weather for the same farm. Our focus is on the effects of varying sheep stocking rates, given different pasture compositions in rotation with cropping under weather and price variations over time and different levels of starting debt. We show how best practice recommendations based on partial costing might mislead by ignoring the powerful cumulative effects of input variability and compounding debts. Increasing production, often already near the achievable water-limited potential, can be of far lower priority than reducing costs and lowering heavy debt burdens. We demonstrate that whole-farm financial risk profiles of a farm’s options provide a richer, more meaningful basis for sound advice.

A Framework for Modelling Whole-Farm Financial Risk.

Abstract: We consider the limitations of optimisation analyses that ignore farm-level financial risks arising from combinations of high fixed costs, including debt burdens and highly variable local weather and prices. A sequential multivariate analysis method is used to compute cumulative distribution functions of decadal whole-farm cash balances for a farm facing highly variable prices and weather, and a level of opening debt. This enables direct probabilistic projections of long-term whole-farm financial viability typical of the Coolamon area in New South Wales. We contrast this with a partial-budgeting linear programming study using average annual prices and weather for the same farm. Our focus is on the effects of varying sheep stocking rates, given different pasture compositions in rotation with cropping under weather and price variations over time and different levels of starting debt. We show how best practice recommendations based on partial costing might mislead by ignoring the powerful cumulative effects of input variability and compounding debts. Increasing production, often already near the achievable water-limited potential, can be of far lower priority than reducing costs and lowering heavy debt burdens. We demonstrate that whole-farm financial risk profiles of a farm’s options provide a richer, more meaningful basis for sound advice.

A Framework for Modelling Whole-Farm Financial Risk

Abstract: We consider the limitations of optimisation analyses that ignore farm-level financial risks arising from combinations of high fixed costs, including debt burdens and highly variable local weather and prices. A sequential multivariate analysis method is used to compute cumulative distribution functions of decadal whole-farm cash balances for a farm facing highly variable prices and weather, and a level of opening debt. This enables direct probabilistic projections of long-term whole-farm financial viability typical of the Coolamon area in New South Wales. We contrast this with a partial-budgeting linear programming study using average annual prices and weather for the same farm. Our focus is on the effects of varying sheep stocking rates, given different pasture compositions in rotation with cropping under weather and price variations over time and different levels of starting debt. We show how best practice recommendations based on partial costing might mislead by ignoring the powerful cumulative effects of input variability and compounding debts. Increasing production, often already near the achievable water-limited potential, can be of far lower priority than reducing costs and lowering heavy debt burdens. We demonstrate that whole-farm financial risk profiles of a farm’s options provide a richer, more meaningful basis for sound advice.