Response of potato (Solanum tuberosum) tuber yield components to gel-polymer soil amendments and irrigation regimes

Two field experiments were conducted to investigate the effects of two gel-polymer formulations (pure and fertiliser-fused) and moisture stress on yield and quality of potato (Solanum tuberosum). The experiments were carried out at the Hatfield Experimental Farm of the University of Pretoria, South Africa. Six gel-polymer rates, consisting of pure gel polymer at 1.5 kg/m(3) of soil, with 85% and 70% fertiliser rate of the control, and fertiliser-fused gel polymer at 1.5, 2, and 3kg/m(3) soil, and control (without gel polymer) were assigned to the subplots. Four maximum allowable moisture depletion (MAD) levels, 25%, 40%, 55%, and 70% of the plant available soil moisture, were allocated to the main plots. Rate of phosphorus (P) was the same for all treatments (168kg/ha). Total nitrogen (N) and potassium (K) budget for the treatments (except one pure gel-polymer treatment received 85%) were balanced to 70% of the control. The fertiliser-fused gel polymer showed no substantial improvement in tuber yield parameters for all rates. The pure gel polymer, especially at higher fertiliser rate, improved total and marketable tuber yield. Marketable tuber number and yield, and total tuber mass showed declining trend with an increase in MAD. Significant reduction in tuber fresh and dry mass was observed at the 55% and 70% MAD irrigation levels. Both high and low soil moisture levels reduced tuber specific gravity. Incidence of common scab was inversely related to the irrigation frequency.