| Abstract: | The diagnosis of Zn deficiency in cotton by means of total analysis or the appearance of deficiency symptoms is unsatisfactory. In order to obtain a better understanding of the development of Zn deficiency symptoms in relation to Zn content cotton plants were cultivated in waterculture under reproducible environmental conditions and Zn deficiency induced by different means. It was observed that deficiency symptoms developed equally, regardless of the inducing factors such as low Zn in the nutrient solution, high nutrient solution pH, high Ca and high Fe supply. High amounts of P in the nutrient solution did not induce Zn deficiency symptoms. Zn deficiency symptoms appeared first as interveinal chlorosis in the medium-aged leaves. The internodes remained short. Later red spots appeared on the leaf blades. The leaves suffering from deficiency were thicker because of enlarged palisade cells. The total Zn content of the leaves did not correlate with the symptoms. Different fractions of the Zn in the leaf (extractable with water, NaCl solution, hydrochloric acid) gave no better results. The analytically determined and calculated Zn fractions are discussed in relation to Zn deficiency inducing conditions. |
