S13 - Session P1 - Soil water and fertilizer retention and bulk density as improved by gel polymer

Authors: Bahlebi Eiasu *

To improve soil physical and chemical properties, thereby to enhance soil water and nutrient retention and availability to plants, fertilizer-fused gel polymer (Aqua-Soil TM , a formulation consisting of 40% K-linked co-polymer, 30% 3:2:3 (42RS) fertilizer, 15% vermiculite, and 15% gypsum)) and pure gel polymer (Stockosorb), both at 0, 2.0 and 1.5 kg/m3 soil, were applied to two soil types (sandy and sandy clay loam soils) in 10-litre pots and field (at the Experimental Farm of the University of Pretoria, South Africa). In addition water holding capacity of free Aqua-Soil and Stockosor was tested. Aqua-Soil and Stockosorb absorbed water as much as 67 and 139 times of their own masses, respectively. Both gel-polymers formulations induced significant increase in soil moisture retention by up to 24% and consistently minimized evaporation rate (by 95%) without remarkable changing in the water retention of the soils at permanent plant wilting point. This indicates that the extra moisture retained in the gel polymer amended soils was available to plants. Soil bulk density consistently decreased with an increase in the rate of the gelling component in the gel polymer formulations. As a result the lowest bulk density was recorded for the pure gel polymer (1.04 g/cm3) and the highest in the control treatments (1.4 g/cm3). Fertilizer-fused gel polymer increased nitrogen retention 76%. These results suggest that fertilizer-fused gel polymer could have a substantial contribution towards increasing soil and water productivity and minimizing environmental pollution, essentially for orchards of tree/perennial crops.