Improvement in Soil Productivity with Long-term lantana (Lantana camara L.) Additions in Rice-Wheat Cropping – I. Effects on Some Soil Properties and Zinc Fractions

To investigate the effects of lantana additions on soil productivity in rice-wheat cropping, a long-term field experiment was started in 1988 with four levels of lantana (0, 10, 20 and 30 t ha⁻¹, fresh weight) and three levels of N (45, 67.5 and 90 kg N ha⁻¹ to rice, corresponded to 50, 75 and 100% of recommended N). The order of these N levels was reversed to 120, 90 and 60 kg N ha⁻¹ to wheat which was again corresponded to 100, 75 and 50 per cent of recommended N. Additions of lantana over the seven years, significantly increased pH, organic carbon (OC) and CEC of the soils. Among various Zn fractions, non-specifically adsorbed exchangeable (Zn I), specifically adsorbed exchangeable (Zn II) and organically bound (Zn III) Zn showed an increase; AI and Fe oxide bound (Zn IV) Zn showed a decrease, and Mn oxide bound (Zn V) and residual (Zn VI) Zn did not show any change due to lantana additions. Lantana additions also increased the DTPA extractable Zn in soils. Although, all the Zn fractions except one (Zn VI) revealed inter-dependency strong association was observed among Zn I, Zn II and Zn III forms. From DTPA extractable Zn point of view, the most important Zn fraction was Zn I followed in decreasing order by Zn III and Zn II, respectively. Residual Zn did not show any relationship with pH, OC or CEC of the soils whereas Zn II was related negatively with all these soil properties. The remaining Zn fractions had positive and significant relationships with all these soil properties except Zn IV which did not bear any association with soil pH.