Influence of summer legume residue recycling and varietal diversification on productivity,energetics, and nutrient dynamics in basmati rice–wheat cropping system of western Indo-Gangetic Plains

A field experiment was conducted on summer mungbean residue recycling (SMBRR) and basmati rice–wheat cropping system (BRWCS) at New Delhi, India. The SMBRR enhanced the system productivity and net returns by ～19.1% and 22.1% compared to summer fallow (SF) with highest magnitude under genotypic sequence of P 2511/HD 2967. Two genotypes each in basmati rice (PB 1 and P 2511) and wheat (HD 2967 and HD 2733) responded well to SMBRR with respect to grain yield efficiency index (GYEI) ≥ 1.0. SMBRR also registered ～13.5% higher microbial biomass carbon (MBC) than SF. Soil organic carbon (SOC) storage also increased by ～6.8% in 0–30 cm soil layer. The rice–wheat–summer mungbean system produced significantly highest energy efficiency compared to the rice–wheat–summer fallow system with highest values under genotypic sequence of P 2511/HD 2967 as a result of better yield expression. Overall, SMBRR with suitable genotypic sequence improved the system productivity, profitability, and nutrient dynamics in BRWCS, which are vital for long-term sustainability of this system.     

Rodent abundance triggered switch between the relative mutualism and predation in a rodent–seed system of the subtropical island forest

Density-dependent non-monotonic species interactions are important in maintaining ecosystem stability and function, but empirical evidences are still rare. Rodents, as both seed dispersers and seed predators, have dual effects on plant regeneration and may result in non-monotonic rodent-plant interactions. According to the non-monotonic models, the relative positive or negative effects of rodents on seedling establishment can be measured based on the positive or negative association of seedling recruitment rate and rodent abundance. In this study, we investigated the fates of acorns of Quercus serrata by tracking tagged seeds on 21 fragmented subtropical islands in the Thousand Island Lake, China. We found that the proportion of germinated seeds of all released seeds showed a dome-shaped association with rodent abundance per seed. The proportion of removed seeds and cached seeds showed a saturated- and a weak dome-shaped association with rodent abundance per seed, respectively. Our results demonstrated a clear empirical evidence that rodent abundance per seed triggered a switch between the relative mutualism and predation in a rodent–seed system. Our study implied that the observed non-monotonic interactions between plants and animals may play a significant role in maintaining biodiversity and ecosystem function. We appeal for more investigations of the complex non-monotonic interactions in various ecosystems.     

Growth and weed suppression ability of common and new cover crops in Germany

Cover crops have a wide-ranging influence on the agroecosystem and create multiple benefits for farmers. A major benefit of cover crops is the suppression of weeds during fall and winter, which can help to reduce soil tillage and herbicide use. However, only a small number of cover crop species are currently grown in Germany. To enlarge this number, four new cover crop species including tartary buckwheat, forage radish, red oat and grain amaranth were tested in comparison with common cover crop species such as white mustard, oilseed radish and phacelia. Emergence, soil coverage, dry matter production and weed suppression ability was assessed for all cover crop species. White mustard emerged faster than all other cover crops and produced the highest amount of shoot dry matter at both locations in southwest Germany twelve weeks after planting (WAP). Oilseed radish was the only cover crop that reduced the weed dry matter in all experiments eight WAP. Phacelia was able to reduce weed density by 77% at Meiereihof twelve WAP. Tartary buckwheat offered the highest soil coverage four WAP, produced the greatest shoot dry matter eight WAP and reduced weed dry matter by more than 96% at Meiereihof and Ihinger Hof twelve WAP. Forage radish produced the highest root dry matter and reduced spring weed density by more than 81% in all experiments. Red oat and grain amaranth emerged slowly, produced less biomass than other cover crops and did not suppress weed growth. The results show that tartary buckwheat and forage radish are well suited as new cover crops in Germany due to their fast growth and good weed suppression ability.     

Crop and cattle production responses to tillage and cover crop management in an integrated crop–livestock system in the southeastern USA

Integrated crop–livestock systems can help achieve greater environmental quality from disparate crop and livestock systems by recycling nutrients and taking advantage of synergies between systems. We investigated crop and animal production responses in integrated crop–livestock systems with two types of winter cover cropping (legume-derived N and inorganic fertilizer N), two types of tillage [conventional disk (CT) and no tillage (NT)], and whether cover crops were grazed by cow/calf pairs or not. The 13-ha field study was a modification of a previous factorial experiment with four replications on Ultisols in Georgia, USA. Recurring summer drought severely limited corn and soybean production during all three years. Type of cover crop had little influence and grazing of cover crops had minor influence on crop production characteristics. Cattle gain from grazing of winter cover crops added a stable component to production. No-tillage management had large positive effects on corn grain (95 vs. 252 g m⁻² under CT and NT, respectively) and stover (305 vs. 385 g m⁻²) production, as well as on soybean grain (147 vs. 219 g m⁻²) and stover (253 vs. 375 g m⁻²) production, but little overall effect on winter wheat grain (292 g m⁻²) and stover (401 g m⁻²) production. Our results suggest that robust, diversified crop–livestock systems can be developed for impoverished soils of the southeastern USA, especially when managed under no tillage to control environmental quality and improve resistance of crops to drought.     

Carrying capacity for finfish aquaculture. Part I—Near-field semi-analytic solutions

The ecosystem carrying capacity for aquaculture cage farming in South Australia is based on guidelines that the maximum feed rates (and farmed fish biomass) be determined such that the concentration c of a given dissolved nutrient does not exceed a prescribed value (say c_P). The problem then is one of relating the nutrient flux F, due to feeding, to the tracer concentration c. To this end the evolution of concentration is modelled using the depth-averaged advection–diffusion equation for a constant source flux F over a finite area cage (or lease) and for both constant and time dependent (tidal) velocities. The divergence theorem is applied to this equation to obtain a new scale estimate of the relation between the flux F and the maximum concentration c_max of a nutrient in the cage region: c_max ≈ F·T*, where T* is a time scale of cage “flushing” that involves both advection and diffusion. The maximum allowed nutrient flux F (and carrying capacity of fish biomass) can then be simply estimated from: F ≈ c_P/T*. New semi-analytic solutions of the advection–diffusion equation for a finite (cage) source are then derived to explore the physics of concentration evolution for constant and tidally varying currents, and to show that the estimate c_max ≈ F·T* is surprisingly robust and generally within 40% of the exact values for a wide set of advective/diffusive parameters. The results generally should find application in other finite source flux problems in the coastal oceans including desalination plants and waste water outfalls.     

Intercropping soybean and palisade grass for enhanced land use efficiency and revenue in a no till system

Integrated no-till crop and livestock production systems may help rejuvenate degraded pastures, increase land use efficiency (LUE), and increase enterprise revenue. Our objectives were to evaluate: (1) planting date effects on seed yield and nutrient concentration of an early-maturing, no-till system (NTS) soybean (Glycine max) when intercropped with palisade grass (Brachiaria brizantha); (2) dry matter production and protein concentration of the grass pasture after soybean harvest; and (3) overall revenue and LUE for the intercrop system. Experiments were performed during two growing seasons in Botucatu, Brazil using a randomized complete block experimental design. When palisade grass and soybean were sown simultaneously, soybean yield averaged 3.28 Mg ha⁻¹. Similar seed yields were observed when palisade grass was planted either 30 d after soybean emergence (DAE) (3.29 Mg ha⁻¹) or at the soybean reproductive stage R6 (full seed) (3.50 Mg ha⁻¹). Monocrop soybean yield averaged 3.50 Mg ha⁻¹. First cut dry matter forage production was greater when palisade grass was sown at the same time as soybean or 30 DAE of soybean. This indicates that interseeding palisade grass with soybean does not significantly affect soybean nutrition or yield. Intercropping did increase LUE and resulted in 1.6 times more revenue than soybean alone. However, sowing palisade grass at the soybean reproductive stage R6 (full seed) significantly reduced the forage yield compared to early planting.     

Weed community responses to soil type during transition to no-till practice on smallholder farms in Zimbabwe

Understanding drivers of weed density and diversity is essential for the development of weed management strategies. Here, we compared temporal changes in weed density and diversity under no-till (NT) and conventional (CONV) tillage systems in cotton–maize rotations on loam, clay loam and sandy loam soils immediately after transition to NT in Kadoma, Zimbabwe. The effect of tillage system on weed density varied through the growth season and was dependent upon soil type and species composition of the weed community. Although weed responses to tillage system varied amongst species, we identified general trend effects on weed density on specific soils. At 3 weeks after crop emergence (WACE), weed density on loam soils was 76% and 96% higher in NT than in CONV during the 2009/2010 and 2010/2011 seasons, respectively, and on clay loam soils it was 37% and 33% higher in NT than CONV, respectively. Weed densities in NT and CONV were similar across all soil types at 6 WACE during the 2009/2010 and 2010/2011 seasons and at 9 WACE in 2009/2010. Tillage system did not affect weed density during the growth season on sandy loam soils. Weed diversity (Shannon index) was at least 75% higher in NT than CONV on loam and clay loam soils at 3 WACE during both seasons. It is likely these increases in weed densities following conversion to NT will exacerbate already prevalent weed management problems in the smallholder sector. Earlier weeding is recommended to suppress weed emergence and reduce likely associated crop yield losses.     

Metabolite profiling of the response to high-nitrogen fertilizer during grain development of bread wheat (Triticum aestivum L.)

Wheat yield and quality are dependent largely on nitrogen (N) availability. In this study, we performed the first metabolomic analysis of the response to high-N fertilizer during wheat grain development using non-targeted gas chromatography-mass spectrometry (GC–MS). Quality parameter analyses demonstrated that high-N fertilizer application led to a significant increase in grain protein content and improvement in starch and bread-making quality. Comparative metabolomic profiling of six grain developmental stages resulted in identification of 74 metabolites, including amino acids, carbohydrates, organic acids and lipids/alcohol, which are primarily involved in carbon and N metabolism. Under high-N fertilizer treatment, numerous metabolites accumulated significantly during grain development. Principal component analysis revealed two principal components as being responsible for the variances resulting from N-fertilizer treatments. Metabolite–metabolite correlation analysis demonstrated that the high-N treatment group had a greater number of positive correlations among metabolites, suggesting that high-N fertilizer treatment induced a concerted metabolic change that resulted in improved grain development. Particularly, the high-N treatment-mediated significant accumulation of metabolites involved in the TCA cycle, starch and storage protein synthesis could be responsible for the improvement of grain yield and quality. Our results provide new insight into the molecular mechanisms of wheat grain development and yield and quality.     

ICT-based agricultural advisory services and nitrogen management practices: A case study of wheat production in China

Excessive use of nitrogen fertilizer in China and its adverse effects on agricultural production have been a national and global concern. In addition to massive public initiatives to promote sustainable farm practices, grass-rooted innovations are emerging in the niche, many of which take the forms of information and communication technologies (ICT) and digital services. This study examines the effects of ICT-based extension services provided by an entrepreneurial startup on adopting sustainable farming practices. We found no significant reduction in N-fertilizer use for wheat production. But the ICT-based services promoted farmers to adapt N-fertilizer use towards site-specific management. The business model of the entrepreneurial venture faces great challenges in becoming participatory and financially sustainable.