Effect of mixing ratios of superabsorbent polymer and pumice on clay soil properties and crop productivity

Abstract

Water scarcity and poor soil conditions pose substantial challenges to agricultural productivity in arid and semi-arid lands (ASALs), such as Mogotio Sub-County in Kenya. Specifically, the complex problems exhibited in the clay soils that are the most common in such areas. These soils hold water firmly in fine particles, reducing the water availability to plants. They waterlog during rainy seasons, and are compacted after a rainfall event. This makes the conditions unfavourable to crop growth more so the crops that are highly sensitive to water like the bell pepper (Capsicum annuum). In this regard, superabsorbent materials show potential in enhancing soil hydraulic properties and moisture availability. However, the best application of such amendments in clay soils is not well documented. The study was conducted to determine the effect of various mixing ratios of a superabsorbent polymer (SAP) and pumice on soil moisture dynamics using the growth of bell pepper, and to identify the optimum mixing ratio to promote agricultural water management in clay soils. The research utilized a completely randomized design that included treatment combinations of SAP at levels of 0, 5, l0, and l5 kg/ha and pumice at levels of 0, 6250, 12500, and 18750 kg/ha. All treatment combinations were replicated. The data was collected for one cropping season and analysed using analysis of variance in J ohn’s Macintosh Program Pro l7. It consisted soil physical properties (porosity, bulk density, hydraulic conductivity, moisture retention, and available water) and plant performance (growth parameters, number and weight of fruits). The amendment mixing ratios were found to have a significant effect on soil hydraulic properties. The l5 kg/ha SAP and 6250 kg/ha pumice treatment had the highest porosity (60.l8%), the lowest bulk density (1.03 g/cm’), reduced available water, and a 53% increase in yield over the control. However, high concentrations of amendments lowered hydraulic conductivity which could be attributed to pore clogging. The optimal soil conditions were characterized by a balanced enhancement of both water retention and aeration. Physical optimization identified the best amendment rate as l5 kg/ha SAP and 6250 kg/ha pumice. The combinations of various mixing ratios of SAP and pumice have the potential to enhance soil water retention, reduce compaction, and boost bell pepper yield in clay soils in some ASALs. However, disproportionate amendment levels may restrict water movement or root respiration.