Yao-Chi Lu

COVER CROPS IN SUSTAINABLE FOOD PRODUCTION

Cover crops are important components of sustainable agricultural systems. They increase surface residue and aid in the reduction of soil erosion. They improve the structure and water-holding capacity of the soil and thus increase the effectiveness of applied N fertilizer. Legume cover crops such as hairy vetch and crimson clover fix nitrogen and contribute to the nitrogen requirements of subsequent crops. Cover crops can also suppress weeds, provide suitable habitat for beneficial predator insects, and act as non-host crops for nematodes and other pests in crop rotations. This paper reviews the agronomic and economic literature on using cover crops in sustainable food production and reports on past and present research on cover crops and sustainable agriculture at the Beltsville Agricultural Research Center, Maryland. Previous studies suggested that the profitability of cover crops is primarily the result of enhanced crop yields rather than reduced input costs. The experiments at the Beltsville Agricultural Research Center on fresh-market tomato production showed that tomatoes grown with hairy vetch mulch were higher yielding and more profitable than those grown with black polyethylene and no mulch system. Previous studies of cover crops in grain production indicated that legume cover crops such as hairy vetch and crimson clover are more profitable than grass cover crops such as rye or wheat because of the ability of legumes to contribute N to the following crop. A comparative analysis of four reduced-tillage corn based cropping systems at the Sustainable Agricultural Demonstration site showed that the cover crop system with corn following hairy vetch produced the largest average gross margin, followed by the conventional no-tillage system, a manure-based system, and a crown vetch living mulch system. The EPIC model to simulate the long-term economic and environmental impacts of incorporating cover crops into grain production systems in mid-Atlantic states was used. Results based on 60 simulation years indicated that there are tradeoffs between the competing objectives of increased profitability, lower soil erosion, and reduced nutrient and pesticide hazards to surface and groundwater supplies. A corn/soybean two-year rotation was found to be the most profitable, while the cover crop system and the manure system were found to be the most environmentally sound.

An Economic and Environmental Tradeoff Analysis of Sustainable Agriculture Cropping Systems

ABSTRACT This study used the results of a 60-year simulation based on data from the Sustainable Agricultural Demonstration site at the USDA, ARS Beltsville Agriculture Research Center in Beltsville, Maryland, to analyze tradeoffs between profitability and environmental stewardship. Six grain cropping systems included two no-tillage rotations with recommended fertilizer and herbicide inputs, two no-tillage rotations with winter annual cover crops and reduced herbicide and nitrogen inputs, and two reduced-tillage organic rotations. Economic analysis showed that highest gross margins were attained by a cover crop-based system with zero nitrogen inputs (CCZ). Risk analysis showed that the organic systems had lower profit variability across years and, therefore, would be most attractive to risk averse farmers. Both the cover crop-based systems and organic systems had low erosion risks and no risk of herbicide contamination so there were no profit versus erosion or herbicide tradeoffs amongst these systems. All systems had nitrogen runoff that exceeded threshold levels in at least two-thirds of the simulation years. In addition, systems that were lowest in nitrogen runoff were highest in phosphorus losses. This resulted in tradeoffs for risk neutral farmers between higher profitability along with higher nitrogen runoff for the CCZ system versus lower profitability along with lower nitrogen runoff for the organic systems. In contrast, for risk averse farmers, there would be a tradeoff between lower economic risk along with higher phosphorus loss in the organic systems versus higher economic risk along with lower phosphorus loss for the CCZ system. Thus, control of nutrient losses while maintaining profitable production levels represents a major challenge to the design of sustainable cropping systems.

Economic Feasibility Study of Variable Irrigation of Corn Production in Southeast Coastal Plain

ABSTRACT This paper evaluates the economic feasibility of variable rate applications (VRA) of irrigation water in corn production. The data were obtained from an experiment conducted at the site-specific center pivot irrigation facility at Florence, SC, INTERNAT, during the 1999-2001 seasons. The field was divided into 396 plots and a water production function was estimated for each plot to determine the optimal amount of irrigation water for each plot. Net returns from VRA applications were compared with uniform applications. The results indicate that the VRA applications yielded larger net returns than the uniform applications. However, the VRT applications require additional equipment and control. The benefits of reduced irrigation water costs plus the value of increased yields must be greater than the additional costs associated with the VRT application. Because the VRT system used in this experiment was built for experimental research purpose, the costs were much higher than those that would have been used for commercial growers. Even for the commercial system, the additional costs of VRT are more than the benefits of using VRT. Thus, at present, the VRT application of irrigation water is not profitable compared to uniform applications for South Carolina. However, the costs of these equipment and controls are declining over time. Furthermore, the costs would be much smaller when VRT is widely adopted by producers and these equipment and controls are mass-produced.

Soil Conservation Benefits of Large Biomass Soybean (LBS) for Increasing Crop Residue Cover

ABSTRACT Soybeans are planted on approximately eight million hectares (20 M acres) of highly erodible land (HEL) in the United States. Soybean crops have been recognized as deficient in supplying crop residues that reduce soil erosion. A new type of soybean tested at the Beltsville Agricultural Research Center, Maryland, can grow to heights of 1.8-meters (6 ft) or more. The development of the large biomass soybean (LBS) suggested the potential of increased crop residue production to reduce soil loss on erodible soybean lands. An evaluation was conducted of the soil conservation benefits of LBS versus conventional soybean using data from a three-year field experiment. LBS produced more crop residue dry biomass and provided a mean increase of 31 percent more crop residue cover in the spring before mulch tillage and 47 percent more after mulch tillage than conventional cultivars. Soil loss estimates for LBS were much lower than for conventional soybeans as simulated by a revised universal soil loss equation (RUSLE). Breeding for increased residue production in soybeans could produce significant environmental benefits as a soil conservation practice in reducing soil erosion. The conservation benefits of LBS can be realized if enhanced biomass production can be combined with adequate grain production.

Optimal Levels of Irrigation in Corn Production in the Southeast Coastal Plain

ABSTRACT Water is a precious resource and is used in many competing industries. To use water efficiently in crop production, knowledge about crop responses to irrigation water, or the production function, is essential. In this paper, we estimated six production functions, two N-fertilizer treatments for each year in 1999, 2000, and 2001, for corn production using the data from experimental plots in Florence, South Carolina, USA. Optimal levels of irrigation and gross margins under profit-maximizing and yield-maximizing strategies were computed. The results indicate that at the current prices of corn and water in South Carolina, the profit-maximizing strategy conserved more irrigation water and produced larger gross margins than the yield-maximizing strategy. The differences in optimal levels of irrigation water and gross margins between the two strategies became even more significant when the relative water/corn price ratios increased. To find out how demand for irrigation water responds to changes in water prices, demand functions for water were derived and demand elasticities of water were computed. At the current prices of water and corn, the demand elasticities were inelastic, which means that irrigation is not very responsive to changes in the price of water. As the price of water increased, demand for irrigation became more responsive to changes in water prices.

Economic Evaluation of Alternative Production Systems for Fresh-Market Tomatoes in the Mid-Atlantic Region

ABSTRACT Growing competition in tomato production and marketing, in conjunction with environmental concerns, requires innovative systems for fresh-market tomato production that are profitable and environmentally sound. This study evaluated the performance of fresh-market tomato production in systems representing different levels of off-farm inputs from 1997 to 1999 at the Beltsville Agricultural Research Center in Maryland. These experimental systems included different cultivars (‘Sunbeam’, ‘Mountain Pride’), soil mulch practices (bare soil, black polyethylene, compost, hairy vetch cover crop), and fungicide application schedules (no fungicide, weekly application, and application determined by TOMCAST model predictions). Gross margins were computed based on experimental yields, production costs from enterprise budgets for staked and tied tomato crops, and weekly prices at the Baltimore fruit and vegetable wholesale market. The Roys safety-first criterion was used to compare the preferred tomato systems for a risk-averse tomato grower. Gross margins from the hairy vetch system were higher than those from the other mulch systems in 1997, but tended to be lower in the other years. The black polyethylene system had the least overall economic risk, and the hairy vetch system had the highest risk. Gross margins among fungicide treatments were highest in the TOMCAST and weekly-based systems compared to the no fungicide system across all years. Economic risk also was similar in the weekly and TOMCAST systems. These results indicate that the TOMCAST system may be implemented to reduce fungicide applications with no additional economic risk, but that the environmental benefits of the hairy vetch system may require more economic risk to growers.

Efficient Allocations of Irrigation Water and Nitrogen Fertilizer in Corn Production

ABSTRACT N-fertilizer and irrigation water are major inputs to corn production and efficient use of these inputs is essential for profit maximization and resource conservation. To use these inputs efficiently, knowledge about plant responses to N-fertilizer and irrigation water, or production functions, is essential. Corn production functions were estimated using the data from experimental plots in Florence, South Carolina, U.S.A., from 1999 through 2001. There were three irrigation treatments and four N-fertilizer regimes. Several forms of production functions were fitted to the data and the quadratic form of the production function was found to have the best fit for the data. The estimated production functions were then used to determine the optimal levels of water and N-fertilizer applications under both yield-maximizing and profit-maximizing strategies. Results indicate that the yield-maximizing strategy called for more water and N-fertilizer and yielded smaller net returns than the profit-maximizing strategy. In 1999, for example, under the current average prices of corn, water, and N-fertilizer, the yield-maximizing strategy required 667 ha-mm of water and 224 kg of N-fertilizer to produce 10.4 Mg/ha of corn and

Economic and environmental feasibility of variable rate nitrogen fertilizer application with carry-over effects

5.42 of net returns; whereas the profit-maximizing strategy required only 556 ha-mm of water and 174 kg of N-fertilizer to produce 9.87 Mg of corn and

Economics of a Hairy Vetch Mulch System for Producing Fresh-market Tomatoes in the Mid-Atlantic Region

57.38 of net returns. The least-cost combinations of water and N-fertilizer application levels for a given output were also determined. The results provide useful information to farmers to make N-fertilizer and irrigation decisions for profit maximization and for resource conservation.