Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Nutrient availability and wheat growth as affected by plant residues and inorganic fertilizers in saline soils

Auteur : Elgharably, Ahmed Galal

Grade : Doctor of Philosophy PhD (2008)

Université de soutenance : University of Adelaide Australie

Résumé partiel
Over 10% of the world’s land is salt affected. Salt accumulation is a major soil constraint for agricultural sustainability in arable or newly cultivated soils. As a result of salinity, soil chemical, physical and biological properties deteriorate, plant uptake of water and nutrients, particularly P, decreases and plant growth declines. Application of plant residues can enhance the activity of soil microorganisms, the availability of nutrients, including P and the plant uptake of P and growth. Such a practice can also be economically viable as it can reduce the use of P from inorganic sources, maintaining the world’s reserve of P rocks and reducing the price of fertilizers and the environmental pollution often associated with the excessive application of inorganic N and P fertilizers. Little is known about how P, with N in proper form, added from inorganic and/or residue sources can affect wheat growth in the salt affected soils with no confounding pH or sodium adsorption ratio (SAR). Increasing microbial activity, N and P availability and wheat uptake of P by application of N and P from organic and inorganic sources may improve wheat growth and hence productivity under saline conditions. The overall aim of this study was to determine ways for enhancing the activity of microorganisms and increasing the availability of N and P, the uptake of nutrients, particularly P and the growth of wheat by management of fertilization from inorganic and organic sources in saline soils. This study therefore was conducted with the following aims : 1) to investigate the relationship between salinity and P availability ; 2) to assess wheat response to combined application of N and P fertilizers under saline conditions ; 3) to evaluate the effect of plant residue addition on N and P availability and microbial activity in salt affected soils ; 4) to determine microbial response to addition of inorganic N rate and form, and how this will affect N and P availability in a saline soil, and 5) to determine the effect of P added from inorganic fertilizer and plant residue, compared to inorganic P fertilization, on microbial biomass and wheat nutrient composition and growth in a saline soil. In saline soils, P availability can be affected by the salt type and concentration and soil texture. Three experiments were conducted to study the relationship between P availability, soil texture and salinity. The results of the first experiment in which soil was shaken with different concentrations of NaCl or CaCl2 or Na2SO4, indicated that P solubility decreased with increasing concentration of Ca2+, but was not affected by Na+ salts. In the second experiment, P availability (after 24h shaking) decreased with increasing salt concentration up to EC1:5 3.1 dS m-1, increased with increasing P addition (0, 100, 200, 400, 600, 1200, 2500 and 5000 µg P g-1 soil), and was generally higher in sandy soil than in sandy loam soil. In the third experiment (15 days incubation), it was found that P availability significantly decreased one day after P addition which was followed by a further decrease to day 5, but then remained unchanged until day 15. It can be concluded that P availability is reduced in presence of clay, and decreases with increasing concentration of salts, particularly Ca2+, and that the availability of P stabilizes in sandy and sandy loam soils within 2 weeks after addition of P from inorganic source. Increasing N or P fertilization enhanced wheat growth in salt affected soils.

Mots clés s : Wheat Growth. Crops and soil. Fertilizers. Soils, Salts in.

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