Nitrogen and phosphorus dynamics and balances in intensive rice-vegetable cropping systems

Nitrogen and phosphorus dynamics and balances in intensive rice-vegetable cropping systems

Shanhua, Tainan AVRDC Taiwan

1997

p.91-104

S631.3.M6

Overdoses of inorganic nitrogen fertilizers in intensive rice-vegetable cropping systems have created concern about impacts on the environment, product quality, and system profitability. These concerns have prompted demands for better nutrient management practices. Knowledge of nutrient dynamics and balances in the systems is therefore of prime importance in guiding research to reduce environmental risks or, conversely, to develop efficient management practices. Within this context, N and P dynamics and balances under selected rice-vegetable cropping systems were reviewed. A study of rice-vegetable cropping systems in the Philippines found that rates of N and P application exceeded requirements of the vegetables. Applications were sufficient for high yield targets but high yields were seldom attained. Excess N remained in the soil as nitrate which was eventually lost through leaching or denitrification, or both, upon soil flooding for the rice season. The losses ranged from 104 to 549 kg/ha depending upon the crop sequence. Highest losses were in rice-sweet pepper and rice-tomato sequences. The excess P applications resulted in accumulations. Soil P losses to the environment occur mainly through water runoff or soil erosion. These loss mechanisms transport P to surface waters where the nutrient promotes eutrophication. Inserting a catch crop after an over fertilized vegetable crop, adjusting the fertilizer rate to take into account residual nutrients from the previous crop, basing fertilizer rates on realistic anticipated yields, and improving the method and timing of applications will increase nutrient recoveries and therefore reduce losses, and thereby create a more sustainable production stystem.[AS]

Managing soil fertility for intensive vegetable production systems in Asia; Proceedings of an

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