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BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

The Sustainable Agriculture Farming Systems (SAFS) Project has studied the transition to low‐input and organic alternatives in California's Sacramento Valley. This project compares a 4‐yr rotation of tomato (Lycopersicon esculentum Mill.), safflower (Carthamus tinctorius L.), corn (Zea mays L.), and wheat (Triticum aestivum L.) followed by double‐cropped bean (Phaseolus vulgaris L.) in the conventional system and oat (Avena sativa L.)–purple vetch (Vicia benghalensis L.) in the low‐input and organic systems. A conventional 2‐yr rotation (tomato–wheat) is also studied. In 1997 and 1998, we evaluated the transition to alternative systems on soil bulk density, water holding capacity, infiltration and storage, water use efficiency, and ‘Brigade’ tomato yield and quality. No differences in laboratory determinations of soil bulk density and water holding capacity were found; however, in situ water holding capacity was highest in the organic system, lowest in the conventional 4‐yr rotation and intermediate in the low‐input and conventional 2‐yr rotations. In 1998, infiltration during 3‐h irrigations was 0.028 m3 m−1 for the conventional, and 0.062 m3 m−1 and 0.065 m3 m−1 for the low‐input and organic systems, respectively. Similar results were observed in 1997. The alternative systems required more water per irrigation for uniform application, resulting in higher soil water content in the organic systems throughout 1998. Evapotranspiration was higher in the conventional systems in both years relative to other systems. Tomato yields did not differ among systems in either year. Fruit quality was highest in the conventional 4‐yr system.

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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 (NO 3 /NO 2 -N), soluble reactive phosphate (SRP), total suspended solids (TSS), and five-day biological oxygen demand (BOD 5 ) 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), BOD 5 (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 BOD 5 was significantly positively correlated with TN (r = 0.43, p ≤ 0.001), NO 3 /NO 2 -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.