INFLUENCE OF AMMONIUM AND NITRATE NUTRITION ON PLANT GROWTH AND ZINC

ACCUMULATION BY INDIAN MUSTARD

Abstract

The source of N used in fertility practices can affect plant growth, nutrient absorption, and the availability of nutrients. The Zn

phytoextraction potential of plants may be increased by selecting the ratio of ammonium to nitrate for fertility that maximizes

growth and Zn accumulation. The objectives were to determine the effects of Zn supply and different molar ratios of ammonium

to nitrate on growth and Zn accumulation in Indian mustard (Brassica juncea Czern.) and to determine the N fertility regime that

maximizes the total Zn content of the harvestable shoots. In a factorial experiment, B. juncea (accession 182921) was supplied

with two levels of Zn (0.05 and 4.0 mg/liter )in combination with six N treatments with different molar % ratios of ammonium-N to

nitrate-N (0:100, 10:90, 20:80, 30:70, 40:60, and 50:50) for 3 weeks in solution culture. Zinc supplied at 0.05 mg Zn/ liter represents

a common, and non-toxic, level of Zn in solution culture, whereas 4.0 mg Zn /liter has been shown to be excessive for B. juncea

growth. The pH of nutrient solutions generally decreased with increasing proportion of ammonium-N in solutions and with increasing

Zn supply. If the supply of Zn in solution was excessive, plants developed symptoms of foliar chlorosis, and symptoms were severe

if plants were supplied 80% of N as nitrate. Supplying high proportions of nitrate in the nutrient medium stimulated Zn accumulation,

whereas increasing proportions of ammonium-N (up to 50% of the total N) enhanced shoot growth. The Zn phytoextraction potential

of B. juncea was maximized at ~15 mg Zn per plant if the plants received 90% as nitrate and 10% of the total N as ammonium.