Zinc treatments applied to cassava (Manihot esculenta Crantz) setts changes early growth and zinc status of plants

Abstract

Summary. Zinc (Zn) deficiency limited the early growth of cassava (Manihot esculenta Crantz) in nutritional trials on a Zn-deficient lateritic red earth that was replaced after bauxite mining at Weipa (12°28"S, 141°53"E). The symptoms developed at 2 weeks after emergence, despite the band application of 0–32 kg Zn/ha and were not related to rates of Zn or other fertilisers applied to the soil. The Zn deficiency in the cassava plants was attributed to low Zn in setts before root access to soil and fertiliser Zn. Two techniques were studied to establish if they could be used to correct Zn deficiency early in the growth of cassava: one was the fertilisation of cassava plants before cutting the stems for planting setts, and the other was soaking cassava setts in Zn solutions for various times at 101 kPa (atmospheric pressure) or 51 kPa (partial pressure). Setts, after treatments, were planted into pots of lateritic soil from Weipa. Plants grown from setts soaked in ZnSO4 solutions varying from 17.4 to 348 mmol Zn/L did not develop Zn-deficiency symptoms, whereas, 62% of plants grown from either unsoaked setts or setts soaked in water developed symptoms. However, the prior fertilisation of cassava plants failed to decrease the incidence of Zn deficiency in plants and did not increase the Zn concentration in setts. Several treatments in Zn solutions were found to significantly increase the Zn concentration in setts, were not detrimental to shoot emergence nor the subsequent growth of plants, and provided an adequate Zn concentration in leaf blades. These treatments were: soaking in 17.4 or 69.5 mmol Zn/L for 5 h and in 69.5 mmol Zn/L for 0.5 h at 51 kPa; and soaking in 69.5 mmol Zn/L for 5 h and in 139 mmol Zn/L for 0.5 and 5 h at 101 kPa. These treatments could be used to overcome early Zn deficiency in cassava plants where the deficiency is a problem despite the soil application of Zn fertilisers.