Animal manure is a useful resource that could be recycled beneficially for crop production. When applied to the agricultural land, manure can increase grain yield and improve soil fertility. The objective of this study was to assess the influence of variable rate manure applications on grain yield under continuous maize ( Zea mays L.) fields across low, medium and high Management Zones (MZs) in dryland cropping systems. The study was conducted over two consecutive years in northeastern Colorado on a fine-loamy, mixed, mesic Aridic Haplustalfs soil. Treatments included (i) Variable and Constant yield goal manure treatments ranging from 22 to 67 Mg ha -1 and (ii) uniform application of synthetic N fertilizer based on soil testing. Experimental strips were 4.5 m wide and 540 m long spanned across MZs with treatments nested within MZs. Manure applications exhibited positive relationship with grain yield in site-year I (R 2=0.53) and site-year III (R 2=0.98), which were dryland fields in succeeding years. After two years of the on-going study, VYG and CYG manure treatments produced higher grain yield on low MZs as opposed to high MZs. The increased grain yield on low MZ in SY III was due to the increased level of organic matter, mineralized N and increase precipitation. Uniform application of synthetic N fertilizer has shown no improvement in the second year, producing lesser grain yield as opposed to VYG and CYG manure treatments on low producing MZ. Variable rate applications of manure have the potential to significantly enhance maize grain yield of low producing areas of the field. The study suggests that variable rate application of manure has potential to be used as an alternative to or in conjunction with synthetic N fertilizer for improving soil fertility and maintaining or improving grain yield. The key to precision manure management is to find a balance between agronomically and environmentally sound manure application rates across spatially variable soils. The good thing about manure application in dryland farming is that, there is little environmental pollution concern, more especially in semi-arid environment of northeastern Colorado.
