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Impact of herbicide application on soil erosion and induced carbon loss in a rubber plantation of Southwest China

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Rubber plantations are strongly increasing in Xishuangbanna, Southwest China. Herbicide applications controlling the undergrowth may increase erosion potential and carbon export by decreasing plant and litter cover. Quantitative evaluation of the erodibility of rubber systems and the impact of herbicides has not been studied. This study aimed at assessing the impact of herbicide application on soil loss and the induced carbon export in a rubber plantation. Runoff, sediment yield, and total organic carbon (TOC) content in sediments were measured under natural rainfall for one year in a 12-year old rubber plantation subjected to three different herbicide treatments: i) standard application twice per year practiced by the majority of farmers (Hs); (ii) no application to maintain a high understory plant cover (H-); and (iii) bimonthly application (adopted by some farmers) in order to largely avoid understory plant cover (H+). The infiltration rate under different treatments was measured with a rainfall simulator. Monthly measurements of fine root density using soil coring, surface cover, and understory plant cover making photography were carried out. The highest soil and TOC in sediment losses (425 g m-2, 15 g C m-2 respectively) were observed under H+ treatment, while under H- treatment they were strongly reduced (50 g m-2 and 2 g C m-2 respectively). Compared to Hs, H+ increased soil and sediment TOC loss by 34 and 52%, while H- reduced soil and TOC loss, both by 82%. Notably, H- presented high conservation efficiency, reducing sediment yields by 86% for highly erosive rainfall events. The cover and management (C) factor and support practice factor (P) are essential components of the common Universal Soil Loss Equation (USLE) model. We combined the C and P factors into a single value (CP) and, for the first time, derived estimations of annual CP values for a rubber plantation (0.005-0.04) using our data. The dynamic change of the CP factor of plantations during the rainy season was quantified by relating relative soil loss to changes in understory plant cover (PC), which can be expressed as CP = 0.04e-0.028PC (R2 = 0.88, P < 0.0001). Understory plant cover as affected by herbicide application was thus a key factor controlling the soil loss of established rubber systems. This suggests options to improve the soil conservation and biodiversity through reduced herbicide management. © 2016 Elsevier B.V.

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