Nitrogen is the most limiting nutrient for crop production in many of the world's agricultural areas and its efficient use is important for the economic sustainability of cropping systems Furthermore, the dynamic nature of N and its propensity for loss from soil‐plant systems creates a unique and challenging environment for its efficient management Crop response to applied N and use efficiency are important criteria for evaluating crop N requirements for maximum economic yield Recovery of N in crop plants is usually less than 50% worldwide Low recovery of N in annual crop is associated with its loss by volatilization, leaching, surface runoff, denitrification, and plant canopy Low recovery of N is not only responsible for higher cost of crop production, but also for environmental pollution Hence, improving N use efficiency (NUE) is desirable to improve crop yields, reducing cost of production, and maintaining environmental quality To improve N efficiency in agriculture, integrated N management strategies that take into consideration improved fertilizer along with soil and crop management practices are necessary Including livestock production with cropping offers one of the best opportunities to improve NUE Synchrony of N supply with crop demand is essential in order to ensure adequate quantity of uptake and utilization and optimum yield This paper discusses N dynamics in soil‐plant systems, and outlines management options for enhancing N use by annual crops

Enhancing nitrogen use efficiency in crop plants

A green manure (GM) is a crop used primarily as a soil amendment and a nutrient source for subsequent crops. Green manure approaches to crop production may improve economic viability, while reducing the environmental impacts of agriculture. However, such approaches are complex because they depend on interactions between the GM, the environment, and management. We suggest that the research and management techniques developed for synthetic inputs are not adequate for effective GM use. This review provides a conceptual framework to more critically evaluate GM use, and we discuss a limited number of key examples involving GM adaptation and growth, effects on soil organic matter, N release and availability for future crops, and pest control. We explore the deficiencies in our current understanding of GM approaches and argue that economic justification of GM requires provision of multiple services (such as nutrient supply, pest and weed control, and increase of soil organic matter). We propose that future research efforts make improved use of whole systems and participatory strategies to better address both the complexity of GMbased cropping systems and the obstacles preventing farmer adoption of GM approaches. D

http://www.dzumenvis.nic.in/GM%20Crops/pdf/Green%20Manure%20Approaches%20to%20Crop.pdf

Green Manure Approaches to Crop Production: A Synthesis

This is the publisher’s final pdf. The published article is copyrighted by the Weed Science Society of America and can be found at: http://wssajournals.org/loi/wees. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work.

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Herbicide Resistance: Toward an Understanding of Resistance Development and the Impact of Herbicide-Resistant Crops

Agricultural production systems in North America have become increasingly specialized. The lack of diversification has had negative economic, biological, and environmental consequences. One alternative approach to diversify agricultural production is to integrate cash grain cropping with ruminant livestock production. Our objective was to review research applicable to development of diversified crop– livestock systems in the U.S. Corn Belt and discuss research priorities and constraints to adoption of those systems. One form of integration becoming more common in the U.S. Corn Belt occurs through contractual arrangements between spatially separated, specialized crop and livestock production farms. Less common is the spatial and temporal integration of crops and livestock on the same land base, which can occur via rotations of grain crops with perennial pastures, short rotations of grain crops with annual or short-season pastures, and utilization of grain crop residues for livestock grazing. We feel this latter model is truer to the concept of diversification. Based on published research and preliminary results from an integrated crop–livestock system project in Illinois, we suggest that integration of crops and livestock on the same land base offers tremendous potential to diversify farm ecosystems in the U.S. Corn Belt while being economically competitive and more environmentally compatible than prevailing specialized production systems. Although studies have addressed or are applicable to components of crop–livestock systems in humid– cool environments, there remains a need for systems level research and funding opportunities for addressing the complex environment– plant–animal–economic–social interactions associated with integrated crop–livestock systems.

Integrated Crop-Livestock Systems in the U.S. Corn Belt

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Quantitative synthesis on the ecosystem services of cover crops

Cover crops often reduce density and biomass of annual weeds in no-till cropping systems. However, cover crops that over-winter also have the potential to reduce crop yield. Currently, there is an interest in annual medics (Medicago spp.) and other annual legumes that winter-kill for use as cover crops in midwestern grain cropping systems. A 2-yr study was conducted at East Lansing and the Kellogg Biological Station, Michigan, to investigate the influence of annual legume cover crops on weed populations. Two annual medic species [burr medic (M. polymorpha cv. Santiago) and barrel medic (M. truncatula Gaertn. cv. Mogul)], berseem clover (Trifolium alexandrinum L. cv. Bigbee), and medium red clover (Trifolium pratense L.) were no-till seeded as cover crops into winter wheat (Triticum aestivum L.) stubble in a winter wheat/corn (Zea nays L.) rotation system. Density of winter annual weeds were between 41 and 78% lower following most cover crops when compared with no cover control in 2 out of 4 site years, while dry weight was between 26 and 80% lower in all 4 site years. Impact of cover crops on the density of summer annual weeds was infrequent; however, weed dry weights were reduced by 70% in 1995 following burr medic and barrel medic. Dry weight of perennial weeds before corn planting were 35 to 75% lower following annual legumes compared with the control, while weed density was not affected. This study indicated a potential for annual legumes to reduce weed density and growth in no-till corn grain systems.

Weed suppression by annual legume cover crops in no-tillage corn

Severe winter-kill of alfalfa (Medicago sativa L.) in some years prompts the need for emergency forages in northern locations. Three annual medic species-barrel medic (M. truncatula Gaertn. cv. Mogul), burr medic (M. polymorpha L. cv. Santiago), and snail medic [M. scutellata (L.) Mill. cv. Sava]-and berseem clover (Trifolium alexandrinum L. cv. Bigbee) and 'Nitro' alfalfa were seeded in early spring at East Lansing and the Kellogg Biological Station (KBS) in Michigan in 1994 and 1995. Forage mass was measured at first harvest 60 d after planting and at second harvest 30 d later. Forage mass of annual medics at first harvest ranged from 0.8 to 3.6 Mg ha -1 across locations and years. Berseem clover produced an average forage mass of 2.2 Mg ha -1 at first harvest, which was similar to alfalfa. Crude protein (CP) concentration of annual medics, berseem, and alfalfa ranged from 111 to 210, 178 to 233, and 170 to 218 g kg -1 , respectively, at first harvest. Regrowth of annual medics (except Mogul) was less than alfalfa or berseem clover; however, the regrowth of Mogul was decumbent and not suitable as hay. Average forage mass and CP concentration of berseem at second harvest was 1.8 Mg ha -1 and 191 g kg -1 , respectively, which was similar to alfalfa. Our results indicate that both annual medics and berseem clover can be used as emergency forages in northern locations; however, annual medics have the potential for only one harvest, whereas berseem can be harvested twice during the growing season.

Annual Medics and Berseem Clover as Emergency Forages

Cropping systems that reduce chemical fertilizer N requirements in winter canola (Brassica napus L.) need further study. Studies were conducted in 1994/1995 and 1995/1996 at two locations in Michigan i) to quantify the N accumulated at plowdown by berseem clover (Trifolium alexandrinum L.), alfalfa (Medicago sativa L.) and three annual medic species (Medicago truncatula Gaertn., M. polymorpha L., and M. scutellata L.) when they were managed as green manure or managed as forage; ii) to compare N response of the winter canola crop following the legumes; and iii) to estimate the N fertilizer replacement value (FRV) of the legumes. The legumes were seeded in early May in both years. Winter canola was planted after legume plowdown 90 d after planting (DAP). Four N rates (0, 50, 100, and 150 kg N ha−1) were applied to the winter canola in early spring. Herbage N yield at plowdown was highest (103.9 kg N ha−1) in berseem clover managed as green manure and this treatment resulted in the highest winter canola yiel...

John M. Squire

Papers

Weed suppression by annual legume cover crops in no-tillage corn

Annual Medics and Berseem Clover as Emergency Forages

Annual legumes as green manure and forage crops in winter canola (Brassica napus L.) rotations.