Estimation of Water Balance Variables in the SRI Paddy Field by Considering Soil Moisture

Abstract

Water Balance analysis in the System of Rice Intensification (SRI) paddy field is essential to evaluate water management regarding its water productivity and water use efficiency. In the observed field, however, particular water balance variables are not easily measured since the methods are often costly, complicated and time consuming. The current study proposed the novel method to estimate non-measurable water balance variables by considering monitored soil moisture in the field by using Excel solver estimation. The field experiment was conducted by adopting SRI rice cultivation in the SRI experimental field in Nagrak Organics SRI Center, Sukabumi, West Java, Indonesia during the first rice season 2010/2011 (October 2010 to Februari 2011, wet season). Results of the developed model showed satisfactory result between observed and estimated soil moisture with the values of R2 higher than 0.70 in the all growth stages. Accordingly, each estimated water balance variable has reasonable trend and value. We found that total inflows through precipitation and irrigation water were 1331.8 and 107 mm, respectively. Meanwhile, the water has leaved the field through crop evapotranspiration, runoff and percolation with their total values were 296.5, 1010.7 and 116 mm, respectively. Minimum irrigation water was needed to meet plant water requirement since no standing water and high precipitation occurred in the current wet season. Also, the total crop evapotranspiration and percolation were low according to the FAO values as the results of low reference evapotranspiration and reduction of hydrostatic pressure, respectively. On the other hand, high runoff was estimated because almost precipitation was drained directly and only retained the water in the field to meet crop evapotranspiration.