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Effect of cultivation on the nitrogen fertility of selected agro-ecosystems in South Africa






Fertilizer Research 42(1-3): 27-32

Effect of cultivation on the nitrogen fertility of selected agro-ecosystems in South Africa

Surveys of soils on commercial farms practising rainfed agriculture in South Africa, found large losses of N fertility. Information regarding the pattern of this loss is not available for different agro-ecosystems. Thus, the aim was to quantify the effect of cultivation on the N fertility of soils in five agro-ecosystems with virgin soils serving as reference, find the relation between the period of cultivation and the decrease in N fertility for each agro-ecosystem and determine whether this decline differed between the agro-ecosystems. Five to six sites with different cultivation periods were sampled within each agro-ecosystem. At each site a cultivated soil and its virgin counterpart were sampled to 200 mm depth and total and mineralizable N were determined as indices of N fertility. Cultivation, irrespective of the period, caused a significant decrease in the N fertility of all five agro-ecosystems and the rate of loss was rapid during the first few years of cultivation. Thereafter, the rate decreased until an equilibrium was approached. In agro-ecosystems from the warmer, drier regions, an equilibrium was approached much sooner than in agro-ecosystems from the cooler, wetter regions, but the percentage of N fertility loss was larger in the latter regions. The percentage loss of mineralizable N was larger than that of total N. This depletion of N fertility in cultivated soils may result in unsustainable crop production.

Accession: 002811410

DOI: 10.1007/bf00750497

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