Sugarcane planting patterns control ephemeral gully erosion and associated nutrient losses: Evidence from hillslope observation

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Globally, the hillslope currently supporting sugarcane production is accelerating soil erosion and nutrient losses that degrade agroecosystem services and increase water pollution. However, sugarcane planting patterns (SPP), involving the arrangement of perennial (P) and newly planted (NP) sugarcane along hillslopes, may influence hillslope erosion and nutrient losses due to changes in root density and litter cover. Yet, no study to date has investigated the contribution of SPP to rill/and ephemeral gully (EG) erosion and associated nutrient losses. Thus, we investigated changes in EG erosion and losses of total nitrogen (TN), phosphorus (TP) and soil organic carbon (SOC) in response to SPP and the underlying mechanisms on hillslopes. Five hillslopes with different SPPs (P–P–P, NP–P–P, P–NP–P, NP–NP–P and P–NP) were identified in a sugarcane growing watershed. Annual EG erosion rates ranged from 56.6–96.1 Mg ha−1 yr−1 in the order of P–P–P < P–NP–P < P–NP < NP–P–P < NP–NP–P. The average EG erosion and associated TN, TP and SOC losses from the newly planted sugarcane fields were 2–3-fold of the perennial fields. The average annual yield of newly planted sugarcane was 10 % higher than the perennial sugarcane, but the increased yield benefit was dwarfed by significant increase in EG erosion and nutrient losses. Simple regression analyses indicated that EG erosion was inversely correlated with sugarcane litter cover and fine root density (root diam. < 1 and 1–2 mm), but positively correlated with slope-length factor. The principal component regression (PCR) showed that fine root density, litter cover, and slope-length were the main predictors for EG erosion. The results of this study revealed that appropriate SPP that replaces perennial sugarcane, at ≤30 % on different slope positions, with newly planted sugarcane, could minimize rill and EG erosion and nutrient losses as well as maintaining the annual yield.