Soil Micronutrients and Phosphorus Stratification As Affected By Long-Term 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 and environmental sustainability in semi-arid cropping systems. This study examined the long-term effects of nitrogen (N) fertilizer management (N rates of 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), micronutrient distribution and soil acidity in a dryland wheat-sorghum-fallow cropping system. Results showed soil organic matter, iron and zinc concentrations were greater with NT compared to tillage treatments. Similarly, NT increased P accumulation in the upper 0-7.5 cm soil depth. After 40-yr of tillage and N fertilizer application, there was a marked decline in pH at the soil surface (0 to 15 cm) with increasing N application,  regardless of tillage intensity. Averaged across N rates, soil surface pH was lower with NT (5.7) compared to CT (6.3) and RT (6.2) systems. Iron and manganese concentrations increased with increasing N application rates, probably 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 levels or strategic tillage to reduce nutrient stratification.