Abstract
During the period 1992-1995 two field experiments were carried out, in order to evaluate the effect of three species of green manure in rotation with potato cultivation. Thus, the effectiveness of Canavalia ensiformis, Mucuna aterrimum and Crotalaria juncea were compared with two control treatments: the first (no green manure, no nitrogen fertilizer) and the second one (with mineral fertilizer, 160 kg.ha-1). The effectiveness of several species depended directly on the volume of green matter and nutrient contents that these contribute, which was related among other factors to seeding time. From the three species evaluated, Canavalia ensiformis had the best behavior, carrying out the highest contributions of green matter and nutrients to the soil. With this species, potato yields surpassed by 7-14 t.ha-1 the control and mineral fertilization variants, respectively. Mucuna aterrimum and Crotalaria juncea had, on the other hand, intermediate behaviors with potato yield increments of up to 8 t.ha-1 compared to the control treatment, these being similar to the variant with mineral fertilization. Green manures increased the contents of available P and exchangeable cations of the soil, as well as NPK absorption for the cultivation. The green manure used proved to be an alternative not only of chemical fertilizer substitution but of soil fertility improvement and yield increments for potato cultivation under the conditions studied.
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