ABSTRACT

This research was carried out to determine maize (Zea mays L) requirement of Zn, Cu, Mn and Fe fertilization, through a correlation and calibration test, in laboratory, greenhouse and field studies between 2008 and 2009 in soils of Southeastern Nigena. For this purpose twenty surface (0-20 cm) soil samples were collected from 20 locations in Southeastern Nigeria to ascertain the status of available micronutrients, examine the efficiencies of 5 extractants for predicting available micronutrients in soils, estimate critical levels of Zn, Cu, Mn and Fe by 5 extraction methods and to establish the optimum rates of the Zn, Cu, Mn and Fe fertilizers requirement for maximum maize production in soils of Southeastern Nigeria. The field experiments were carried out in two successive growing cropping-seasons in coastal plain sands derived soils at Akpabuyo, Cross River state, Nigeria in the degraded tropical rain forest zone. The first stage of the experiments was done in greenhouse conditions with 4 replications and maize var. Oba super II was grown. Four different doses of micronutrients (Zn, Cu, Fe and Mn) fertilizers at (0, 4, 8, 10, and 12 kg/ha) were applied to each pot, while in the second stage of the studies (0.0, 2.0, 4.0, 6.0, 8.0, 10.0, and 12.0 kg ha 1) of Zn, Cu, Fe and Mn fertilizer were applied in the field experiments, in randomized complete block designed (RCBD) with 4 replicates as ZnSO4.7H20, CuSO4.5H20, MnSO4.5H20 and Fe2SO4.5H20, respectively. The results obtained showed that, the soils were generally strongly acidic with values ranging from 4.19 to 5.48. The soils were predominantly sandy ranging from loamy-sands (LS); sandy-barns (SL); sandy-day-barns to clayey loam. Total N, available P and exchangeable K content were very high in soils used for the greenhouse studies but, these were found low in the case of field experiments. The available Zn and Cu content by different extraction methods were found to be low in the soils while, Fe and Mn were considered moderate and varied significantly (P<0.05) with the extractants used. Coca-cola solution among others was recommended as the best extractant for predicting available Zn and Cu in the soils evaluated while 0.1 M HCl solution was equally recommended as the best extractant for predicting available Fe and Mn contents of the soils under review. The estimated critical levels of Zn, Cu, Fe and Mn by the 5 extraction methods are recommended for use to predict or interpret soil and plant test values for these nutrients in soils of southeastern Nigeria and in similar soils. Maize plant height, dry matter, concentration and uptake were increased with increase levels of applied Zn, Cu, Fe and Mn fertilizers in soil. The determined optimum rates of Zn, Cu, Fe and Mn requirement for maximum maize production in soils of southeastern Nigeria, were found to be 9.5 kg Zn ha 1, 10.1 kg Cu ha 1, 11.3 kg Fe ha', and 11.3 kg Mnha', respectively. In the field studies, the application rates of 7.7, 9.5, 8.5 and 9.0 kg ha' of Zn, Cu, Fe and Mn fertilizers respectively, are achievable to meet both maize grain yields and other growth parameters over a period of two or more cropping seasons (residual) in soils of southeastern Nigeria.