Effects of biosolids and an inorganic mulch on soil-plant relationships in two Chihuahuan Desert grasslands
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In-depth research is needed to understand the effects of biosolids (sewage sludge) application on plant growth in semiarid regions. The objectives of this research were to determine the effects of surface application of biosolids on soil properties and plant growth on two Chihuahuan desert grasslands sites during two years. A tobosagrass (Hilaria mutica) site with a Stellar very fine sandy loam soil and a blue grama (Bouteloua gracilis) site with a Jal fine sandy loam soil were selected on the Sierra Blanca ranch, in Texas. Biosolids at 0,18, and 34 Mg ha^-1 were applied either in the dormant or growing season to experimental plots in 1997 or 1998. An inorganic mulch (synthetic fiber-floor pads, "IM") was applied to simulate ground cover of biosolids rates. Supplemental irrigation was provided to half of the plots throughout the growing season. Afternoon soil temperature, soil-volumetric water content, and soil NO3-N were measured throughout the growing season. Plant tissue nitrogen concentration (TKN) was measured in August and October on both tobosagrass and blue grama in 1998. Standing crop was measured in October for both grasses. In general, soil temperature decreased under application of both mulches at both sites during the two years. Soil-water content was higher under application of both mulches at both sites at most sampling dates. Nitrate-nitrogen in the soil increased with application of biosolids during both seasons of application with a more pronounced effect from biosolids applied during the dormant season during the first year of application on both sites. Nitrate-nitrogen in the soil slightly increased with inorganic mulch application on both sites. The dormant application of biosolids promoted earlier improvement of soil properties compared to growing season application of biosolids during the first year of application at both sites. Tobosagrass TKN remained similar with biosolids application in August and October and decreased with IM application in October. In contrast, blue grama TKN increased with biosolids rates in October and was not affected by mulch application in any date. Standing crop of both grasses increased with application of both mulches and irrigation. Biosolids increased NO3-N in the soil and improved plant forage quality more than the inorganic mulch in both sites and years.