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Land use conversion of row crops to bioenergy cropping systems in the southeastern United States (U.S.) creates concerns associated with water use and NO 3 -N leaching. Production of energy from biomass is associated with large amounts of byproducts generated during biofuel processing. Biochar and vinasse are two nutrient rich byproducts that could be land-applied to bioenergy crops to reduce reliance on synthetic fertilizer. However, effects on water dynamics of applying these byproducts to support biomass production is poorly understood, particularly when bioenergy crops replace traditional row crops. Thus, this study aimed to compare a cotton ( Gossypium hirsutum L.)-peanut ( Arachis hypogaea L.) rotation to sweet sorghum [ Sorghum bicolor (L.) Moench] receiving annual applications of biochar and vinasse, on biomass yield, crop evapotranspiration, water use efficiency (WUE), NO 3 -N leaching, and soil volumetric water content. A field study was conducted from 2013 to 2015 to assess the following treatments: cotton + 150 kg N ha −1 (COT), peanut + 30 kg N ha −1 (PEA), and sweet sorghum receiving one of the following i) 30 kg N ha −1 (S30); ii) 30 kg N ha −1 + biochar (S30B); iii) 30 kg N ha −1 + vinasse (S30V); and iv) 150 kg N ha −1 (S150). Similar aboveground dry matter yields were obtained in 2013 and 2015 for cotton and all sweet sorghum treatments and were on average 19 Mg ha −1 for both years. S30 and S150 achieved similar yields. Sweet sorghum and COT exhibited the highest WUE (∼5 g kg −1 ). S30B increased soil moisture retention at 0–0.2 m depth 36, 29, and 24% in 2013, 2014, and 2015, respectively. Biochar incorporated at 0.15 m soil depth increased soil moisture retention down to 0.4 m. Low N rate application combined with biochar in S30B could represent an alternative management practice to minimize N leaching, recycle nutrients, and increase soil water retention if sweet sorghum were to be widely adopted by farmers in the southeastern U.S. [ABSTRACT FROM AUTHOR]

Changing pasture land to the production of bioenergy crops will affect regional water dynamics. Returning by-products of industrial conversion of bioenergy crops like fermentation residual or biochar back to the field could be used to improve sustainable nutrient management, but could also impact water quantity and quality in ways that are poorly understood. The objective of this study was to assess the effects of land-use conversion from low-input bahiagrass ( Paspalum notatum Flüggé) pastures to elephantgrass [ Pennisetum purpureum (L.) Schum.] for bioenergy production under different nutrient management practices on biomass yield, crop water dynamics and nitrate-nitrogen (NO 3 -N) leaching during growing and dormant seasons. Treatments evaluated were 1) bahiagrass + 50 kg N ha −1 ; 2) elephantgrass + 50 kg N ha −1 ; 3) elephantgrass + 50 kg N ha −1 + fermentation residual; 4) elephantgrass + 50 kg N ha −1 + biochar; and 5) elephantgrass + 250 kg N ha −1 . Data were collected on crop evapotranspiration (ET), water use efficiency, drainage, NO 3 -N leaching, and aboveground dry matter accumulation. Dry matter yield of elephantgrass was 4- to 7-fold greater than bahiagrass after the first growing season, but was similar among elephantgrass treatments. Elephantgrass produced with no residual amendments reduced drainage (approx. 43% across all growing seasons) compared to bahiagrass, and this reduction was exacerbated in the residual treatments. Reduced drainage was associated with increased ET. Elephantgrass, regardless of treatment, reduced the amount of NO 3 -N lost through drainage compared to bahiagrass. Therefore, replacing bahiagrass with elephantgrass will increase cropping system water use and diminish the rate of groundwater replenishment during the growing season, which could have detrimental effects for other ecosystem processes that rely on this water resource. However, elephantgrass increased the efficiency with which water was used to produce biomass and reduced NO 3 -N leaching to groundwater. [ABSTRACT FROM AUTHOR]