Nutrient depletion from soils by intensive cultivation and changes in phosphorus fractions [electronic resource].

Includes references.

The present investigation was carried out to study the effect of intensive alfalfa cultivation on the possible depletion of P, K, Fe, and Cu from soils. Further work was carried out to identify changes in the relative abundance of P fractions. A pot experiment was designed in the greenhouse to simulate the nature overstretching scenario of intensive cultivation. Five surface soil samples of different textures were used to support intensively cultivated alfalfa for a total of six cuts. Measurements were taken to determine dry matter production, nutrient uptake, levels of elemental availability in soils, and the P fractions. The data indicate that the dry matter yield of alfalfa declined "as ,a". function of progressing cuts but not necessarily in a linear trend. Some soils were able to sustain a flourishing dry matter accumulation before reverting to the falling trend. With the possible exception of Cu, the total uptake of nutrients was closely related to the soil clay content. On the average of all soils, the initial available P and K decreased by 52 % after the final harvest, whereas Fe decreased by only 40 %. Huge amounts of P and K were mined from the soils, reaching 70 and 500 kg per feddan from the two nutrients, respectively. All P fractions were markedly affected by the intensity of cultivation. Reductant soluble P shows a loss of only 50 %, indicating that it was rejuvenated. The Fe¬ P fraction was reduced to nil, indicating that it was comprised of young small crystallites that are prune to decomposition. It is recommended that calibrated soil management programs should be adopted to make up for nutrients mined by intensive cultivation. The alternative is soil degradation.

Summary in Arabic.

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