Relation of amounts and forms of P to Maize(Zea Mays)yields following PAPR application
Kalipenta, Kasuba Collins
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The study was part of an on going experiment on the evaluation of PAPR on a number of crops including maize. The part of this study was to determine the amounts and forms of P related to maize yield response.The trials were carried out on five benchmarks soil types in Central, Lusaka and Southern Provinces of Zambia. During the first cropping season (2000/2001), On-Farm and On-Station trials were conducted in agro-ecological Regions I and IL There were three On-Farm trials (GART in Chisamba, Chibwe in Kabwe and Mwanachingwala in Magoye) and three On-Station trials (Kafuku Farm Institute in Mkushi, UNZA Farm and Magoye CDT). PAPR was compared with MAP as a source of P for maize production. Treatment rates were 0, 60 and 120 kg P2O5 ha"' and 0, 40, 80, 120, 160 and 200 kg P2O5 ha"' for On-Farm and On-Station trials respectively. Absolute Zeros were added in the second year to evaluate the natural soil fertility compared to the added nutrients.The available forms and amounts of P were determined by Bray I and the Pi soil tests from the first season's soil samples. Results of the soil tests from 0 - 15 cm and 15-30 cm were regressed on maize yield. For GART, only P by Bray 1, in the 0 - 15 cm (surface layer) was significantly (P 0.05) related to the maize yield. At Mwanachingwala and UNZA Farm, maize yield was responding to additional P in the 15-30 cm soil horizon The increase in maize yield response verified the low initial soil P at the above sites. At Kafuku Farm Institute, the response was to higher rates of fresh and residual application of P which maintained a higher soil solution P concentration resulting in significant increase in yield response. At all sites except Kabwe, there was response to both fresh and residual application of both sources of P. The fresh application of PAPR was more effective than MAP at Mwanachingwala. The residual effect of PAPR and MAP was similar at all sites except UNZA Farm where the residual effect was more for PAPR than MAP.This study indicates that the available forms of P at the experimental sites for maize uptake were only H2PO4, HP04. This is deduced from the soil pH and Bray 1 determination and verified by the Pi test.Other nutrients other than P (N,K,S) were limiting for all sites and the extent varied from site to site. The effect of lime application was dependent upon site. Liming increased maize yields where exchangeable aluminum was high and at sites were Ca was deficient. Depression of maize yields was observed were there was a probable inbalance of Ca/Mg cations for normal plant growth.
- Agriculture