Evaluation of super absorbent polymer on soil water storage, crop growth, yield, and water productivity of rice-groundnut cropping system

AbstractIn eastern India, rice is the principal crop during the kharif season. During rabi season (post-rainy), the area is not fully utilized for crop production and is kept fallow mostly due to low residual soil moisture, coupled with lack of irrigation. Besides this, the soil in this region (mostly Alfisols) is characterized by shallow, coarse texture, low water-holding capacity (WHC), poor soil organic matter (OM), and poor soil fertility, and is subjected to soil erosion. The WHC of coarse textured soils can be improved by soil amendments or conditioners such as farmyard manure (FYM), tank soil, hydrophilic polymers, etc. Due to the unavailability of a sufficient quantity of FYM/compost, super absorbent polymers (SAP) can be used to improve soil WHC, water use efficiency (WUE), restrict soil erosion and runoff, and increase plant performance. Therefore, an attempt has been made to study water retention and release characteristics of a potassium polyacrylate-based polymer and to evaluate its effect on soil water storage, crop growth, yield, and WUE of the rice-groundnut cropping system. It was observed that 0.25% and 0.50% SAP-treated soil took 6.5 and 7.5 hrs, respectively, to come to 100% water absorption (saturation). However, in control (sand without any SAP), 100% water absorption was achieved within 0.25 hr. At saturation, the gravimetric water content in control, 0.25% SAP, and 0.50% SAP was 25%, 109%, and 181%, respectively. When normal soil reached the permanent wilting point (4% soil moisture on w/w) in eleven days after saturation, the soil moisture content was 93% and 145% in 0.25% and 0.50% SAP-treated soil, respectively. However, the use of SAP up to 100 kg per ha did not affect soil moisture storage, plant growth, and yield characteristics of rice and groundnut crops significantly in a sandy loam soil of eastern India. Further research on SAP should consider the optimal application rate for different soils and crops, water absorption in the presence of chemical and organic fertilizer, the aging effect on the soil properties and plant characteristics, and its environmental and economic consequences.