Aref A. Abdul-Baki

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.

Hypochlorite and tissue sterilization.

SummaryTrace amounts of sodium hypochlorite that remain on the surface of seeds (Lycopersicon esculentum Mill.) after sterilization interfere with subsequent uptake and incorporation of leucine into protein when the seeds are used in metabolic studies. The hypochlorite can be washed away with 0.01 N HCl but not by washing several times with water.

Foliar Disease in Fresh-Market Tomato Grown in Differing Bed Strategies and Fungicide Spray Programs

A 3-year field study in central Maryland evaluated foliar disease in fresh-market tomato grown using combinations of four bed strategies and three fungicide programs. Bed strategies included uncovered beds with or without a composted dairy manure amendment or beds covered with black polyethylene or hairy vetch mulch. Fungicide programs included no fungicide, weekly fungicide, or fungicide applications scheduled according to the TOMCAST disease predictor. In plots with hairy vetch-covered beds, early blight caused by Alternaria solani, Septoria leaf spot caused by Septoria lycopersici, and defoliation were lower versus uncovered beds each year. Early blight and defoliation were lower in beds covered with vetch versus polyethylene mulch in 2 of 3 years. Disease severity, defoliation, and marketable yield were similar for the weekly and TOMCAST fungicide programs, with 40 to 50% fewer sprays using TOMCAST. Marketable yield was similar among bed strategies except for higher yields in covered versus uncovered and unamended beds in a relatively wet year and lower yields in vetch versus polyethylene beds in a dry year.

A conservation-tillage, cover-cropping strategy and economic analysis for creamer potato production

A two-year experiment was conducted at the Beltsville Agricultural Research Center (BARC), MD, and Virginia Polytechnic Institute and State University Kentland Agricultural Research Farm (KARF), VA, to evaluate potato (Solanum tuberosum L.) production of 32- to 57-mm-size-range tubers (referred to hereafter as creamers) in a conservation-tillage, cover-cropping strategy. The experiments used a split-plot design in which the main-plots were cover crop treatments and the sub-plots were different potato selections. Main plot treatments included rye (Secale cereale L.), crimson clover (Trifolium incarnatum L.), Austrian winter pea (Pisum sativum L.), rape (Brassica napus L.), oat (Avena sativa L.), rye/crimson clover mixture, rape/crimson clover mixture, bare soil/raised beds, and bare soil/flat beds (control). Potato selections tested were B1145-2, B1491-5, and B1492-12 in 2000 and B1145-2, B1102-3, and B0811-4 in 2001. Yields in the conservation-tillage treatments were equal to or better than those in the bare soil/flat bed control with few exceptions. Large-sized tubers (<57 mm) in almost all cases remained below 6% of total marketable yield even when the tubers were harvested late. Delayed harvest did not reduce creamer-sized yields nor did it increase yield of large-sized tubers. Economic analysis shows that net returns from some conservation-tillage treatments are equal to or higher than the conventional-tillage strategy and confirms the viability of the conservation-tillage, cover-cropping strategy. Furthermore, the conservation-tillage strategy in many cases allows timely planting using machinery in the wet soils of Maryland and Virginia during the narrow window of spring potato planting time, whereas the conventional tillage strategy does not offer this advantage.ResumenUn experimento de dos años de duración fue realizado por el Centro de Investigación Agrícola de Beltsville (BARC), MD y el Instituto Politécnico de Virginia en la Granja de Investigación Agrícola Kentland de la Universidad del Estado (KARF), VA, para evaluar la producción de tubérculos de papa (Solanum tuberosum L.) de 32 a 57mm de tamaño (referidos en lo sucesivo como “creamers”)) con estrategia de labranza de conservación, cultivo de cobertura. Los experimentos se hicieron empleando el diseño experimental de parcelas divididas, en el cual las parcelas principales fueron con tratamiento de cultivos de cobertura y las subparcelas fueron diferentes selecciones de papa. Los tratamientos de las parcelas principales incluyeron centeno (Secale cereale L.), trébol rojo (Trifolium incarnatum L.), guisante austriaco de invierno (Pisum sativum L.), colza (Brassica napus L.), avena (Avena sativa L.), mezclas de centeno/trébol rojo, colza/trébol rojo, suelo sin labranza/camas altas y suelo sin labranza/camas a nivel (testigo). Las subparcelas incluyeron las selecciones de papa B1145-2, B1491-5 y B1492-12 en el 2000 y B1145-2, B1102-3 y B0811-4 en el 2001. Los rendimientos de los tratamientos de labranza de conservación fueron iguales o mejores, con pocas excepciones, que los de los controles sin labranza / camas a nivel. Los tubérculos de tamaño grande (<57mm) en casi todos los casos estuvieron por debajo del 6% de rendimiento total comerciable aun cuando se cosecharon un tiempo después. La cosecha diferida no redujo los rendimientos de los tubérculos del tamaño “creamer” ni tampoco se incrementó el rendimiento de tubérculos de mayor tamaño. El análisis económico muestra que las ganancias netas de algunos de los tratamientos con labranza de conservación, son iguales o mayores que los de la estrategia de labranza convencional y confirman la viabilidad de la estrategia de labranza convencional, cultivos de cobertura. Más aun, la estrategia de labranza de conservación permite, en muchos casos, la siembra a tiempo, utilizando maquinaria en suelos húmedos de MD y VA, durante la corta temporada de siembra de papa de primavera, mientras que la estrategia de labranza convencional no ofrece esta ventaja.

Biomass Yield and Flower Production in Sunn Hemp: Effect of Cutting the Main Stem

ABSTRACT A field experiment was conducted at the Tropical Research and Education Center, University of Florida, Homestead, to determine the effects on plant morphology, biomass yield, and flower production. of cutting the main stem of sunn hemp (Crotalaria juncea L.) plants at different heights. Seeds treated with cowpea (Vigua unguicalata)-type rhizobium were sown on 15 April 1999. The main stems were cut at 30, 60, and 90 cm above soil surface 100 days after seeding when the plants were about 1.5 m tall. Control plants were left uncut. Biomass that had been cut from plants was included in the total biomass yield. Seventy days following stem cutting, individual plants were evaluated for: plant height; main stem diameter; fresh and dry weights of roots, main stems, primary branches, secondary branches, leaves, open flowers, and unopened flowers. Leaf area and nutritional analyses of the plant parts were determined. Cutting the main stem at 30 and 60 cm above soil surface reduced total plant biomass, whereas cutting at 90 cm height increased biomass yield. Cutting at 30 cm produced the highest quality of biomass by increasing the leaf yield and reducing the weights of root and main stem both of which are low in N and high in C/N. Cutting the main stem at 90 cm produced the highest biomass yield, increased the number and weight of primary and secondary branches and, consequently, increased the number of flowers per plant. Nitrogen was highest in flowers and lowest in roots and main stems. Flowers were highest in K, P, Zn and Cu, whereas roots were highest in Fe content. We conclude that cutting the main stem at 30 cm height and allowing the plants to grow for an additional 70 d result in the highest quality biomass for use as green manure, windbreaks, and mulch. Cutting at 90 cm produced the largest biomass yield and increased flower production.

Evaluation of vegetable production management practices to reduce the ecological risk of pesticides

The ability of agricultural management practices to reduce the ecological risks of pesticides was evaluated. Risk quotients, a mathematical description of the relationship between exposure and toxicity, and hazard ratings, a rank of the potential risk of pesticides to aquatic environments, were calculated for conventional and alternative cultivation practices for tomatoes: Poly-Bare, raised beds covered with polyethylene mulch with bare-soil furrows; Poly-Rye, raised beds covered with polyethylene mulch with cereal rye (Secale cereale) grown in the furrows; and Vetch, raised beds and furrows planted with hairy vetch seed (Vicia villosa). Evaluations were conducted using measured pesticide concentrations in runoff at the edge-of-field and estimated environmental concentrations in an adjacent creek and a theoretical pond receiving the runoff. Runoff from Poly-Bare presented the greatest risk to ecosystem health and to sensitive organisms, whereas the use of Vetch minimized these risks. Previous studies have shown that harvest yields were maintained and that runoff volume, soil loss, and off-site transport of pesticides measured in runoff were reduced using the alternative management practices (Poly-Rye and Vetch). Together, these results indicate that the alternative management practices (Poly-Rye and Vetch) have a less adverse impact on the environment than the conventional management practice (Poly-Bare) while providing growers with an acceptable economic return. In addition, the present study demonstrates the need to consider the management practice when assessing the potential risks and hazards for certain pesticides.

Male fertility of derived tetraploids ofSolanum tuberosum from groups tubersosum x phureja-stenotomum

Four plants of each of 15 derived tetraploids from a cross of B0749-2F (2n=4×=48) and DM91-5 (2n=2×=24) were planted in the greenhouse at Beltsville, Maryland, in January 1992. The female tetraploid parent is a late blight resistant selection from theTuberosum germplasm base. The male diploid parent is a high dry matter selection from the GroupPhureja-Stenotomum germplasm base. For each derived tetraploid, the percent normal, abnormal, and total pollen germinationin vitro were determined on 2–4 flowers per derived tetraploid harvested 3–4 times during a three-week period in April. The percent normal, abnormal, and total pollen germination ranged from 0.6 to 27.5, 0.1 to 7.6, and 1.4 to 36.6, respectively. Pollen tube growth, measured 2 hours from initiation of germination, ranged from 22 to 130 nm. Four general types of abnormalities in the pollen were identified: a) stunted and curly pollen tubes; b) damaged membranes allowing leakage of cytoplasmic contents; c) pollen grains with two or more pollen tubes; and d) split pollen tubes. In hybridizations with Atlantic as the female parent, 11 out of 15 of these derived tetraploids produced viable seeds. All 15 derived tetraploids were female fertile. These results suggest that utilizing derived tetraploids from theTuberosum andPhureja-Stenotomum germplasm bases in future breeding efforts should not present any great difficulty. However, hybridizations involving these derived tetraploids were more successful when the derived tetraploids were the female parent.CompendioCuatro plantas de cada uno de 15 tetraploides obtenidos de un cruzamiento de B0749-2F (2n=4x=48) y DM91-5 (2n=2x=24) fueron plantadas en invernadero en Beltsville, Maryland, en enero, 1992. El progenitor tetraploide femenino es una selección resistente al tizón tardío, procedente de la base de germoplasma Tuberosum. El progenitor diploide masculino es una selección de alto contenido de materia seca de la base de germoplasma del grupo Phureja-Stenotomum. Para cada tetraploide obtenido, se determinó el porcentaje normal, anormal y total de polen germinado in vitro, de 2–4 flores por tetraploide obtenido, cosechado 3–4 veces durante un periodo de tres semanas en abril. El porcentaje de germinación normal, anormal y total varió de 0.6 a 27.5, 0.1 a 7.6 y 1.4 a 36.6, respectivamente. El crecimiento del tubo polínico, medido dos horas a partir del inicio de la germinación, varió de 22 a 130 nm. Se identificaron en el polen cuatro tipos generales de anormalidad: a) tubos polínicos atrofiados y rizados; b) membranas dañadas permitiendo incluso la salida del contenido citoplasmático; c) granos de polen con dos o más tubos polínicos; y d) tubos polínicos rasgados. En hibridaciones con Atlantic como progenitor femenino, 11 de 15 de estos tetraploides obtenidos produjeron semillas viables. Todos los 15 tetraploides obtenidos fueron hembras fértiles. Estos resultados sugieren que el utilizar tetraploides obtenidos de las bases de germoplasma Tuberosum y Phureja-Stenotomum en los trabajos futuros de mejoramiento no habrá de presentar mayor dificultad. Sin embargo, las hibridaciones que incluyeron estos tetraploides fueron más exitosas cuando los tetraploides obtenidos fueron los progenitores femeninos.