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University of the Free State (2019)

Comparison of soil phosphorus fractions after 37 years of wheat production management practices in a semi-arid climate

Ncoyi, Khanyisile

Titre : Comparison of soil phosphorus fractions after 37 years of wheat production management practices in a semi-arid climate

Auteur : Ncoyi, Khanyisile

Université de soutenance : University of the Free State

Grade : Magister Scientiae Agriculturae in Soil Science 2019

Résumé partiel
Wheat production management practices are essential for optimum crop growth and the attainment of higher yields. However, these management practices have an impact on the sustainability of soil fertility and productivity. Therefore, it was important to investigate the impact of these residue management options on some soil fertility indicators such as phosphorus (P) fractions under a semi-arid climate. The aim of the study was to evaluate the influence of wheat residue management practices on soil P fractions in a long-term trial near Bethlehem in the Eastern Free State. The trial was established in 1979 and consisted of two methods of straw disposal (burned and unburned), three primary tillage methods (no-tillage, stubble mulch and ploughing) and two methods of weed control (chemical and mechanical). Representative soil samples were collected in 2016 at various soil depth intervals of 0-50, 50-100, 100-150 and 150-250 mm and analysed for soil P fractions. A sequential extraction procedure was used to differentiate between labile (0.5 M NaHCO3 extractable), moderately labile (0.1 M NaOH extractable), stable (1 M HCl extractable) and residual (concentrated HCl) fractions. Except for the residual P fraction, the total P (Pt) of the other fractions was separated into inorganic (Pi) and organic (Po) P. The straw disposal methods had variable influence on soil P fractions. Burning of wheat residues increased the labile Pi and hence Pt fractions when compared to the unburned residues across all four soil layers. However, the unburned plots had a slightly higher labile Po fraction than the burned plots except in the deepest soil layer (150-250 mm). In the moderately labile P fraction, burned residues resulted in a slightly higher Pi, Po and Pt compared to the unburned residues, except in the 0-50 mm (Pi) and 50-100 mm (Pi, Po and Pt) soil layers. Furthermore, burning of wheat residues increased the stable Pi, Po and Pt fractions when the unburned residues served as a reference. Conversely, the unburned plots had a slightly higher residual Pt fraction in the 0-50 and 50-100 mm soil layers.

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