Iron deficiency depresses growth of furrow irrigated soybean and pigeon pea on vertisols of northern N.S.W

Abstract

Crops under furrow irrigation or after heavy rainfall on the alkaline, calcareous Vertisols of northern N.S.W. frequently exhibit chlorosis of young leaves after the soil is wetted, but the specific cause has not been identified previously. The quantitative effects of the syndrome on growth, physiological activity and yield are also unknown. Experiments on soybean and pigeon pea grown on a Vertisol at Breeza, N.S.W., Australia, examined the influence of applying Fe to the leaves, and Fe, Zn, N+P and lime to the soil before sowing, on leaf colour, leaf photosynthesis, crop dry matter, and yield of grain of soybean and dry matter and yield of pigeon pea. In soybean, chelated Fe applied to the soil before sowing increased the levels of active Fe (Fe2+) in leaves by up to 42% and dry matter of shoots by up to 46% early in the season. Active Fe and dry matter of shoots were linearly correlated (r2 = 0.76). Soil Fe treatments did not affect leaf photosynthesis, although addition of chelated Fe to the soil resulted in greener leaves than in the control. Foliar Fe had no significant effect on active Fe, leaf colour, or leaf photosynthesis. The 9% increase in grain yield in response to application of 20 kg Fe ha-1 to the soil was not significant. In pigeon pea, application of 20 kg Fe ha-1 to the soil increased dry matter by 140% and grain yield by 414%. Effects of lime and zinc were not significant, but N+P increased yield by 112%. The study showed that Fe deficiency is limiting the growth and/or yield of irrigated soybean and pigeon pea on the clay soils of northern N.S.W., and pointed to lime-induced iron chlorosis as a possible mechanism of damage.