Effects of vegetation cover and rainfall intensity on sediment-associated nitrogen and phosphorus losses and particle size composition on the Loess Plateau

Abstract

Vegetation and rainfall are two important factors affecting soil erosion and the resulting nutrients loss on the Chinese Loess Plateau. Field experiments under simulated rainfall condition were conducted to investigate the effect of rainfall intensity and vegetation (Caragana korshinskii) cover on soil loss, sediment-associated nitrogen (N) and phosphorus (P) loss, and particle size distribution (PSD) of the eroded sediment. Treatments included three rainfall intensities (60, 100, and 140 mm h⁻¹ [2.364, 3.94, and 5.516 in hr⁻¹]) with each producing 60 min of rainfall and three plots (0%, 30%, and 80%) with the same gradient of 15°. The results showed that vegetation cover, rainfall intensity, and their interaction all had significant effect on sediment and the associated N and P loss. In general, higher rainfall intensity and lower coverage produced higher sediment and consequently higher nutrient loss but led to a lower enrichment ratio for N (ER_N) in sediments. Vegetation cover had no marked effect on enrichment ratio of P (ER_P). A strong positive linear relation was observed between soil loss and N and P loss. The eroded sediment contained more fine particles (clay and silt, < 20 μm [7.874 × 10^-4 in]) compared to the original surface soil. Under the same cover condition, the percentage of clay significantly decreased with increasing rainfall intensity (p < 0.05). The ER_N and ER_P were positively correlated with ER clay. This suggested that the clay fraction (<2 μm [7.874 × 10^-5 in]) was preferentially eroded and that N and P were mainly adsorbed onto or contained within this particle fraction.