Abstract

HERVE, Dominique; MITA, Víctor  and  COUTEAUX, Marie-Madeleine. Building nitrogen balance in post-fallow potato crops. Ecología en Bolivia [online]. 2006, vol.41, n.3, pp.133-153. ISSN 1605-2528.

In the Bolivian Altiplano the small farmer aims to insure his production against climatic risks without costly chemical inputs. We exposed two questions studied in the European project TROPANDES: how to mobilize in the potato crop the soil nitrogen improvement due to fallowing and what fraction of this stock is still available for a second potato crop? The effect of fallowing on potato yields and of potato crop on its next yield are evaluated with a plant and soil nitrogen balance. Potato-potato rotation (with potato Solanum tuberosum subsp. andigena and bitter potato Solanum x Juzepczukii) after 3 to 5 years fallowing, is evaluated in three sites near the Patacamaya experimental station during 1998-99 and 1999-2000. The plots with low initial soil nitrogen were managed according to the peasant practices, applying ovine dung at potato planting and incorporating crop residues to soil. Treatments against pests and diseases were performed if necessary. Potato leaf, stem, root and tuber biomass, and total nitrogen of each compartment, were measured at harvest time; soil mineral nitrogen was measured at planting and harvesting. The basis for nitrogen balance calculation was defined in potato crops. Nitrogen availability from dung was significant only during the second year. Nitrogen availability from potato residues is very low. Potato needs are very low relatively to the total soil nitrogen. Yield variability is high, mainly due to climate. The crop and soil nitrogen balance was negative at the end of the first potato crop and positive in all treatments at the end of the second potato harvest. This static balance deduces from crop net exportation, the soil N contribution. To analyse the dynamic availability of nitrogen and its synchronisation with the plant requirements, flux analysis is needed.

Keywords : Fallow; Nitrogen balance; Potato; Ovine dung; Bolivian high plateau.

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