Manejo da cobertura do solo e adubação com P e S na cultura da mandioquinha-salsa

Abstract

Population in general is getting more interested in consuming healthy food. Alternative eco-agricultural cropping practices are being emphasized, thanks to the benefits to sustainable agricultural and environment systems. Management of organic and mineral fertilizers, in search of nutrient efficiency, is directly related to environmental, social and economical issues. As plants become more efficient to absorb nutrients, the farmer can count on better products quality and, consequently, to better economic results. The experiments described in the chapters one and two of this study were conducted, respectively, in Fazenda Córrego Frio and in Fazenda Santo Antônio de Estrela, both in Nova Friburgo municipality, Rio de Janeiro State. The first one was accomplished in partnership with Pesagro-Nova Friburgo, and it aimed to evaluate the production of the arracacha (Arracacia xanthorrhiza Bancroft) plant associated with covering plants. The experimental design was of random blocks with four repetitions, and four management treatments: conventional (control), spontaneous vegetation, black oats (Avena strigosa Schreb), and consortium black oats + Villosa villosa. The arracacha variety tested in both studies was the “Amarela de Carandaí” (AC). The results showed that in the treatments with oats and oat + Villosa villosa, the accumulation of dry mass in the plant and their parts was smallest. The production of commercial roots was higher at 12 months after the planting (MAP) for the conventional and spontaneous vegetation treatments. The second experiment aimed to evaluate the yield of the arracacha crop submitted to increasing doses of phosphorus, with two sources of the fertilizer. The experimental design was of randomly blocks with 4 repetitions and 12 treatments, that consisted of 2 phosphorous sources (simple super phosphate and rock phosphate), and 6 phosphorous doses (0 - without phosphorus - control), 40, 80, 120, 240 and 480 kg P2O5 ha-1). The largest production of total and commercial roots was verified in the treatments with rock phosphate as source of P. The highest total levels of sulfur in the plants were found in the treatments with simple super phosphate. Concerning the accumulation of total nutrients, it was observed a similarity between the two sources of phosphorous. A third experiment was conducted in a greenhouse, located in Seropédica municipality - RJ. The experimental design was of randomly blocks with four repetitions and six treatments. The treatments consisted of increasing doses of gypsum (CaSO4H2O) as following: 12.5; 25; 50; 100; 200 kg ha-1 of S and a control without gypsum. The soil material was sampled from an Udult soil and the cultivated variety was “Amarela de Senador Amaral” (ASA). The objective of the study was to evaluate the effect of the sulphur addition in the crop yield. There were determinate: plant dry matter weight; and the levels of N, P, K and S in the plant tissue. The highest doses of S increased the dry matter accumulated in leaves + petioles. Concerning the sulfur accumulation, it was dose dependent for the three parts of the arracacha plant. Despite the conditions in which this research was conducted (greenhouse), it was possible to conclude preliminarily that the ASA is responsive to sulphur fertilization.