Estimated potential impacts of soil and water conservation terraces on potato yields under different climate conditions

Abstract

Terracing is a commonly used soil and water conservation beneficial management practice (BMP) designed to reduce soil water erosion in hilly areas. Former studies indicated that potato (Solanum tuberosum L.) yields in terraced fields appeared to be higher than nonterraced fields, even though the effective cultivation area was smaller due to berm construction in terraced fields. People hypothesized that the observed increase of potato yields was due to increased soil moisture retention caused by terracing. However, testing of this hypothesis is difficult due to lack of long-term complete records of soil moisture data together with potato yield information. The objective of this study is to assess the potato yields of terraced and nonterraced fields under different climate conditions with the assistance of a hydrological model to fill the data gaps. The historical soil moisture contents in fields with or without terraces were estimated by the Soil and Water Assessment Tool (SWAT). Then a stochastic regression model was constructed to assess the impact of soil moisture on potato yields based on 20 years of historical potato yields, estimated soil moisture content, and other biophysical data as inputs. Results showed that terracing could increase potato yields under dry and normal conditions, while nonterraced fields achieved higher yields under wet conditions. Soil moistures on terraced fields were significantly higher than on nonterraced fields. The mean annual potato yields in both terraced and nonterraced fields increased with the Soil Moisture Index (SMI) to an optimum at −1.1, then significantly decreased as SMI increased to above −0.8 or decreased to below −1.4. Statistical analysis confirmed that the optimum SMI for potato productions is around −1.1. In addition, the potato yields within each SMI group do not have significant differences for fields with or without terraces. These results indicated that as a soil and water conservation BMP, terracing could also help to improve potato productivity by improving soil water availability during the growing seasons of dry and normal years. However, the excessively high soil moisture trapped by terraces could lead to potato yield reduction during wet years. The results of this study could provide critical information for potato yield predictions and soil and water conservation BMP cost-benefit analysis under different climate conditions.