Tillage And Beef Cattle Manure Effects On Soil Nitrogen In A Dryland Rotation

Minimum tillage practices used in dryland cropping systems that reduce soil water evaporation and erosion may also decrease efficiency of manure nutrient utilization. We initiated a study in 1997 to investigate the effects of surface-applied stockpiled and composted beef cattle (Bos taurus) manure on soil N and sorghum [Sorghum bicolor (L.) Moench] and wheat (Triticum aestivum L.) yields and N-uptake within a wheat-sorghum-fallow dryland crop rotation. Paired terraces with no-tillage (NT) and stubble-mulch tillage (ST) systems were main plots of a single rotation phase. Stockpiled manure, composted manure, or commercial fertilizer (urea + ammonium phosphate) were applied prior to sorghum planting to supply estimated Nand P requirements of sorghum and wheat for a 3- year period. Phosphorus-based manure or compost treatments also received supplemental urea. Unfertilized treatment checks were included for yield and nutrient comparisons. Sorghum grain yield in 1999 exhibited a significant (P \u3c 0.05) response to tillage and fertilizer treatments. Plots receiving urea had 22% greater yield and 16% greater N-uptake than manure and compost amended plots. Moreover, manure and compost sorghum yields were no different or slightly lower than those of the unfertilized plots. Wheat was a good scavenger of residual N accumulated throughout the fallow period although grain yield was not affected by N treatments and tillage. Residual NO3--N after harvest and N-uptake were significantly greater under ST as compared with NT. Tillage may be required to maintain higher mineralization rates and permit a more efficient use of manure N