Runoff-related nutrient loss affected by fertilization and cultivation in sloping croplands: An 11-year observation under natural rainfall

Abstract

Fertilization and cultivation play important roles in affecting nitrogen (N) and phosphorus (P) losses from sloping croplands. However, the extent and magnitude of these effects are still unknown. Fifteen plots (8 m in length, 4 m in width) were constructed in a representative purple sloping cropland (15°) to determine the fertilization and cultivation effects on runoff-related N and P losses from 2008 to 2018. Five treatments (3 replications for each), including no fertilizer with downslope cultivation (CK), combined manure and chemical fertilizers with downslope cultivation (T1), chemical fertilizer with downslope cultivation (T2), 1.5-fold chemical fertilizer with downslope cultivation (T3), and chemical fertilizer with contour cultivation (T4), were examined. The results showed that there were significant differences in runoff depth, sediment yield, total N (TN) and total P (TP) loss amounts among the five treatments (P < 0.05). The loss amounts of TN, nitrate-nitrogen (NO3-N), ammonium-nitrogen (NH4-N) and TP were the highest in CK and lowest in T4. T1 presented lower TN and TP losses than T2. Total dissolved N (TDN) accounted for 57.97–70.34% of TN loss while total dissolved P accounted for 18.74–31.28% of TP loss in runoff, demonstrating that TDN and particulate P dominated the N and P losses. Runoff depth exhibited significant positive correlations with TN, NO3-N, and NH4-N concentrations (P < 0.05). Our results highlighted that manure application and contour cultivation markedly reduced the N and P losses in sloping croplands, and the risk of N loss caused by unit erosive rainfall decreased with the monitoring years.