ISSN:
1573-5036
Keywords:
alfisol
;
immobilization
;
mineralization
;
nitrogen-15
;
savanna
;
tropical agrosystems
Source:
Springer Online Journal Archives 1860-2000
Topics:
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
Notes:
Abstract A field experiment was designed to follow the fate of fertilizer nitrogen in an annual crop (maize) and a permanent meadow (Digitaria decumbens) cultivated on an alfisol under the tropical two-season-climate of the Venezuelan Llanos.15N labelled urea equivalent to 150 kg N.ha−1 was added to field plots and to lysimeters of undisturbed soil. Results obtained after the first year show that the accumulation of fertilizer nitrogen was twice as great in the aboveground parts of maize and accompanying weeds (29% of the added nitrogen) than in the aerial parts of grass (16%), while the reverse trend was shown by roots: about 2% of the added nitrogen was detected in corn roots and more than 4% in the underground biomass of the meadow. Leaching losses were less than 2% under maize and almost nil under pasture in spite of intensive leaching which occured during the rainy season. The top-soil (0–40 cm) of the grassland retained about 50% of the fertilizer nitrogen while only about 25% remained in the top-soil of the maize plot. The loss of fertilizer could be explained, largely, either by volatilisation immediately after application, or denitrification during the following weeks. The relative proportions of fertilizer-N and soil-N in maize and grass suggest that, during this period, gross mineralization of soil-N in both agroecosystems attained a value almost equivalent to the total nitrogen added in the fertilizer. The implications of these results when converting natural savannas into cultivated regimes are very different in the case of permanent pasture, which can improve the organic status of these poor soils and annual crops, like maize, which induce an unavoidable deficit in the nitrogen balance.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF02220810
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