Limitation to Sweet Potato growth in small volumes of soil imposed by water and nutrient stress, acidity and salinity.

Abstract

Sweet potato (Ipomoea batatas (L) Lam.) is an important smallholder root crop in Papua New Guinea, and there is an increasing requirement for its use as a diagnostic test species in agricultural research programs. As a result, it was decided to investigate sweet potato growth under conditions of water and nutrient stress, soil acidity and soil salinity using procedures with a small volume (1.7 L) of potted soil. An Orthoxic Tropudult soil deficient in phosphorus (P) and sulfur (S) from the Highlands Agricultural Experiment Station at Aiyura was assessed. Well-defined growth responses were apparent from about 10 days after sowing Water stress dramatically reduced growth As water stress increased, vines decreased in length and had fewer leaves, lower whole plant (tops plus roots) fresh weights and lower dry top weights. Water stress also masked effects of nutrient stress Nutrient stress (P and S deficiency) reduced whole plant fresh weight and dry top weight without affecting vine length or number of leaves. Phosphorus and S requirements for 90% of maximum yield were equivalent to 48 and 25 kg ha'1, respectively. Sweet potato proved intolerant of soluble salts at the high level (electrical conductivity of 1:5 soil .water extract 1 87 dS nr1) imposed. Application of lime raised pH (1:5 soil .water) from 5.0 to 5.8, but had little effect on growth. Limitations on plant size and period of growth imposed by a small volume of soil strongly suggest that soil water must be maintained between field capacity and 50% of field capacity if other factors (e g. nutrition) are to be effectively assessed and extrapolated to the field.