Durga D. Poudel

Comparison of soil N availability and leaching potential, crop yields and weeds in organic, low-input and conventional farming systems in northern California

Increasing dependence on off-farm inputs including, fertilizers, pesticides and energy for food and fiber production in the United States and elsewhere is of questionable sustainability resulting in environmental degradation and human health risks. The organic (no synthetic fertilizer or pesticide use), and low-input (reduced amount of synthetic fertilizer and pesticide use), farming systems are considered to be an alternative to conventional farming systems, to enhance agricultural sustainability and environmental quality. Soil N availability and leaching potential, crop yields and weeds are important factors related to agricultural sustainability and environmental quality, yet information on long-term farming system effects on these factors, especially in the organic and low-input farming systems is limited. Four farming systems: organic, low-input, conventional (synthetic fertilizer and pesticides applied at recommended rates) 4-year rotation (conv-4) and a conventional 2-year rotation (conv-2) were evaluated for soil mineral N, potentially mineralizable N (PMN), crop yields and weed biomass in irrigated processing tomatoes (Lycopersicon esculentumL.) and corn (Zea mays L.) from 1994 to 1998 in California’s Sacramento Valley. Soil mineral N levels during the cropping season varied by crop, farming system, and the amount and source of N fertilization. The organic and low-input systems showed 112 and 36% greater PMN pools than the conventional systems, respectively. However, N mineralization rates of the conventional systems were 100% greater than in the organic and 28% greater than in the low-input system. Average tomato fruit yield for the 5-year period (1994–1998) was 71.0 Mg ha −1 and average corn grain yield was 11.6 Mg ha −1 and both were not significantly different among farming systems. The organic system had a greater aboveground weed biomass at harvest compared to other systems. The lower potential risk of N leaching from lower N mineralization rates in the organic and low-input farming systems appear to improve agricultural sustainability and environmental quality while maintaining similar crop yields.

Impacts of cropping systems on soil nitrogen storage and loss

Abstract Organic and low-input cropping systems that use more C inputs are alternatives to conventional systems for sustaining long-term soil fertility. An understanding of the impacts of these cropping systems on N balance (N applied minus N removed in harvested plant material), storage and loss is necessary to improve long-term soil fertility and minimize the risk of environmental pollution. An evaluation of 4-year rotations of organic (N from legumes and composted manures), low-input (N from legumes and reduced amounts of synthetic fertilizers), and conventional (conv-4, N from synthetic fertilizers) and a conventional 2-year rotation (conv-2, N from synthetic fertilizers) on N balance, storage and loss was conducted from 1989 to 1998. Compared to the conv-2 system, the organic and conv-4 systems showed 119 and 8% greater cumulative N balances, respectively, over the duration of the study. However, N balance in the low-input system was 19% less than in conv-2 system. After 10 years of differential management, total N in the top 15 cm of soil was 1.46 g kg−1 in the organic, 1.26 g kg−1 in the low-input, 1.13 g kg−1 in the conv-4, and 1.1 g kg−1 in the conv-2 system. Compared to the conv-2 system, cumulative N losses for the organic, low-input and conv-4 systems were lower by 80, 92, and 10%, respectively. These findings suggest that organic and low-input cropping systems that add C to soil have the potential for storing N and making it available for future crop use, while minimizing the risk of environmental pollution.

The sustainable agriculture farming system project in California 's Sacramento Valley

The Sustainable Agriculture Farming Systems project (SAFS) was established in 1988 to study the transition from conventional to low-input and organic crop production practices. The project includes four-year crop rotations under conventional (conv-4), low-input, and organic management and a conventionally managed, two-year rotation (conv-2). Positive effects on soil quality resulting from low-input and organic management include increased soil organic matter, a reduction in soil-borne diseases, increased pools of P and K, higher microbial biomass and activity, an increase in mobile humic acids and increased water infiltration rates and soil water-holding capacity. Pesticide use in the low-input cropping system is about 25% of that used in the conventional systems. The most profitable farming system continues to be the conv-2 system due to the greater frequency of tomato in that rotation. Among the four-year rotations, the organic system, in which the produce commands premium prices, is the most profitable, although least profitable if premium prices are not applied. Information generated from SAFS research has been disseminated via videotape, workshops, annual field days, field tours, educational materials, peer-reviewed articles and an Internet homepage. Future challenges for the SAFS project include development of reduced-tillage and cover crop management strategies to optimize N availability following cash crops, weed management in organic and low-input systems, improvement of water-use efficiency in alternative systems and sequestration of C in the soil.

Changes of Tomato Yield and Fruit Elemental Composition in Conventional, Low Input, and Organic Systems

ABSTRACT The Sustainable Agriculture Farming System (SAFS) Project was begun in 1988 to compare conventional 4-year and 2-year rotations receiving synthetic fertilizers and pesticides to low input and organic farming systems. In 1998 and 1999, we evaluated the influence of 10 years of organic, low input, and conventional management practices on soil chemical properties, processing tomato yields, and fruit mineral composition. The organic system had highest soil total C, N, soluble P, exchangeable Ca, and K levels as a result of 10 years of manure application and cover crop use. In both years, fruit yields were similar in the three farming systems. Organic fruits contained highest amounts of P, and Ca. Conventionally-grown tomatoes were richer in N, and Na, while the low input system had an intermediate values for N, P, and Na, and the lowest Ca concentration of the three systems.

Assessment of seasonal and spatial variation of surface water quality, identification of factors associated with water quality variability, and the modeling of critical nonpoint source pollution areas in an agricultural watershed

Surface water quality impairment in agricultural watersheds is a major environmental concern in the United States. To assess seasonal and spatial variability of surface water quality and identify factors associated with surface water quality variability, we monitored surface water quality at seven locations in Bayou Plaquemine Brule Watershed in Louisiana twice monthly from March of 2002 to February of 2008 and performed multivariate analyses of the dataset. Using the Soil and Water Assessment Tool (SWAT) model, we identified critical areas of nonpoint source pollution in the watershed. While temperature, turbidity, dissolved oxygen (DO), conductivity and pH were determined in the field using YSI Sonde (YSI Incorporated, Yellow Springs, Ohio), surface water samples were analyzed for total nitrogen (TN), total phosphorus (TP), nitrate/nitrite-N (NO3/NO2-N), soluble reactive phosphate (SRP), total suspended solids (TSS), and five-day biological oxygen demand (BOD5) in laboratory. The monthly water quality sampling included a regular sampling and an after-rain-event sampling. Average DO for the summer months, March through November, was 4.91 ± 0.08 mg L−1 (4.91 ± 0.08 ppm), while average DO for the winter months, December through February, was 8.32 ± 0.12 mg L−1 (8.32 ± 0.12 ppm). Dissolved oxygen was negatively correlated with TN (r = −0.22, p ≤ 0.001), SRP (r = −0.17, p ≤ 0.001), TP (r = −0.17, p ≤ 0.001), BOD5 (r = −0.25, p ≤ 0.001), and surface water temperature (r = −0.70, p ≤ 0.001). Turbidity was strongly correlated with TSS (r = 0.59, p ≤ 0.001), suggesting that most turbidity in the water body comes from suspended solids. Similarly BOD5 was significantly positively correlated with TN (r = 0.43, p ≤ 0.001), NO3/NO2-N (r = 0.26, p ≤ 0.001), TP (r = 0.25, p ≤ 0.001), and SRP (r = 0.18, p ≤ 0.001). Results of factor analyses showed sediment, phosphorus (P), nitrogen (N), surface water temperature, dissolved solids, and acidity/alkalinity as the most important factors associated with surface water quality variability in this watershed. Although relatively higher concentrations of sediments, TP, and TN were observed in the upper reaches of the watershed based on water quality monitoring, the SWAT simulation results showed the critical nonpoint source pollution areas of sediment, P, and N in the lower reaches of the watershed. Lower reaches of the watershed have mainly rice and crawfish production, while the upper reaches include primarily sugarcane, pasturelands, and soybean production. Information on seasonal variability of surface water quality, factors associated with surface water quality variability, and the critical areas for nonpoint source pollution will be valuable inputs for developing a watershed management plan for effective nonpoint source pollution control in an agricultural watershed.

Hands-On Activities and Challenge Tests in Agricultural and Environmental Education

Many agricultural and environmental problems are interrelated and overlapping. Several agencies, including nonprofit organizations, have developed programs to educate schoolchildren about agricultural and environmental issues; however, programs that integrate both agricultural and environmental learning, especially among middle and high school students, are limited. To facilitate agricultural and environmental learning among middle and high school students, an agricultural and environmental challenge program was developed at the University of Louisiana at Lafayette (UL Lafayette) in southwestern Louisiana. Educators conducted 4 challenge events for middle and high school students in 2002. Each event consisted of 5 stations: water quality, plant science, soil science, land management, and aquaculture. Groups of 5 to 6 students spent 25 min at each station engaged in hands-on activities and discussion. At the end of each event, appropriate tests were administered, and prizes and a scholarship to study in the College of Applied Life Sciences at UL Lafayette were awarded. Students evaluated the events at the end of the day. Teachers and students reported that the events were very interesting, informative, and educational. Hands-on activities and challenge tests enhanced students interest, motivation, and ability to think critically about contemporary agriculture and environmental issues in the region.

An analysis of commercial vegetable farms in relation to sustainability in the uplands of Southeast Asia

Abstract Commercial vegetable production systems in the uplands of Southeast Asia are important to supplement the demand for fresh vegetables in lowland Asian cities. A farm survey and soil sampling was done to characterise and identify major factors limiting vegetable productivity in the uplands of the Manupali watershed, Mindanao, the Philippines. Large yield differences were found among the four most common crops: tomato (Lycopersicon esculentum), cabbage (Brassica oleracea var. capitata), potato (Solanum tuberosum), and Chinese cabbage (Brassica pekinensis). The most closely correlated factors with crop yields were: nitrogen application rates for tomato and cabbage; topsoil per cent sand and fungicide usage for potato; and reliance on family labor for Chinese cabbage. Following multivariate data analysis, two vegetable farming systems were identified: the higher external nutrient (HEN) and the lower external nutrient (LEN) systems. To enhance their sustainability, both systems should adopt more appropriate soil conservation practices, cropping sequences, and plant protection techniques. Additionally, the LEN farmers should increase nutrient application, while the HEN farmers would benefit from labor saving technologies, crop diversification, and more judicious fertiliser application.

Identification of SSR markers associated with saccharification yield using pool-based genome-wide association mapping in sorghum

Saccharification describes the conversion of plant biomass by cellulase into glucose. Because plants have never been selected for high saccharification yield, cellulosic ethanol production faces a significant bottleneck. To improve saccharification yield, it is critical to identify the genes that affect this process. In this study, we used pool-based genome-wide association mapping to identify simple sequence repeat (SSR) markers associated with saccharification yield. Screening of 703 SSR markers against the low and high saccharification pools identified two markers on the sorghum chromosomes 2 (23-1062) and 4 (74-508c) associated with saccharification yield. The association was significant at 1% using either general or mixed linear models. Localization of these markers based on the whole genome sequence indicates that 23-1062 is 223 kb from a β-glucanase (Bg) gene and 74-508c is 81 kb from a steroid-binding protein (Sbp) gene. Bg is critical for cell wall assembly and degradation, but Sbp can suppress the expression of Bg as demonstrated in Arabidopsis (Yang et al. 2005). These markers are found physically close to genes encoding plant cell wall synthesis enzymes such as xyloglucan fucosyltransferase (149 kb from 74-508c) and UDP-D-glucose 4-epimerase (46 kb from 23-1062). Genetic transformation of selected candidate genes is in progress to examine their effect on saccharification yield in plants.

Asian vegetable production systems for the future

Abstract To assist in vegetable research decision-making relevant to the developing countries of Asia, an analysis of agroecological zonation (AEZ) for vegetable-production areas was undertaken. In contrast to grain legumes, vegetable-production areas were found to span AEZs, due largely to the anthropomorphic nature of vegetable-production systems. In broad terms, characterization of vegetable-production systems can be based upon distribution of temperature and rainfall, with three categories recognized: cool highlands, warm-dry, and warm-wet lowlands. Because of pressing environmental concerns for resource management in fragile highlands, and the demographic upturn in cities, vegetable-production research should concentrate on resource management. In highland and peri-urban systems such will help ensure enhanced vegetable-production without compromising the opportunity for future welfare and income of the population at large.

SUSTAINABILITY OF COMMERCIAL VEGETABLE PRODUCTION UNDER FALLOW SYSTEMS IN THE UPLANDS OF MINDANAO, THE PHILIPPINES

The quality of fallow lands in northern Mindanao, the Philippines, was assessed with a farm survey and soil sampling in order to understand land-use dynamics under upland commercial vegetable production systems. Twenty-one percent of com- mercial vegetable growers practiced fallow systems, with an average re-cultivation period of four years. The soils of the fallow lands were highly acidic, nutrient poor, and higher in exchangeable aluminum compared to lands currently under cultivation. Land fal- lowing was more prominent on large farms and those with higher farm labor requirements. Two distinct groups of land fallowers were identified. The first represented fallowers with a positive net return from vegetable crops while the second, and larger, group represented land fallowers with negative net return from vegetable crops. Re-cultivation of fallow lands was more common in the second group. To rejuvenate fallow lands, timber tree planting was the most preferred option of the first group while fruit trees were preferred by the second group. In light of the apparently slow rate of soil fertility regeneration, the lack of capital among most land fallowers, and the increasing demand for arable land to raise farm income, planting of trees on cultivated lands before their being set aside as fallow for natural fertility regeneration is suggested as a potential measure to increase farm income and the sustainability of upland commercial vegetable production under fallow systems.