Changes in soil surface chemistry after fifty years of tillage and nitrogen fertilization

Knowledge gained on the long-term effects of crop management practices on soil fertility is critical in developing nutrient management strategies to optimize crop yields. This study examined the long-term effects of nitrogen (N) fertilizer application rates (0, 22, 45 and 67 kg N ha(-1)) and tillage intensity [conventional tillage (CT), reduced tillage (RT) and no-tillage (NT)] on soil phosphorus (P), micronutrients and soil acidity in a dryland winter wheat (Diticum aestivum L.) - sorghum (Sorghum bicolor L.)- fallow cropping system. Results showed soil organic matter (SOM), iron (Fe) and manganese (Mn) concentrations were greater under NT compared to CT or RT. Similarly, NT (32 mg kg(-1)) increased P accumulation in the upper 7.5 cm soil depth compared to CT (21 mg kg(-1)) or RT (26 mg kg(-1)). After 50-yr of tillage and N fertilizer application, pH at the soil surface (0 to 7.5 cm) declined markedly with increasing N application, ranging from 6.4 with the unfertilized control to 5.7 when 67 kg N ha(-1) was applied. Averaged across N rates, Delta pH in the soil surface over the 50-yr was greater with NT compared to CT or RT treatments. Iron and Mn concentrations increased with increasing N application rates, possibly due to the decrease in pH associated with N application. Based on our findings, growers adopting NT need to monitor changes in soil surface chemistry and take necessary corrective measures such as liming to maintain satisfactory pH and nutrients levels to optimize crop yields.