Planting density and yield of cassava roots Densidade de plantio e rendimento de raízes de mandioca

In Mata Fresca, an area located on the border of the states of Rio Grande do Norte and Ceará, in Brazil, small farmers have a source of income from the production of cassava roots, using planting densities of around 5,000 plants ha-1. This procedure might be helping to limit higher yields of the roots, since some studies have shown that it is possible to obtain higher yields of cassava using higher densities. The objective of this study was to evaluate the root yield and other characteristics of the cassava, as a response to planting density. The Vermelhinha cultivar was submitted to planting densities of from 5,000 to 21,000 plants ha-1, at intervals of 2,000 plants ha-1, in an experiment under irrigation. A completely randomized block design with four replications was used. The ideal planting densities in order to maximise leaf green matter, stems and branches, total roots, total marketable roots, number of marketable roots, marketable-root dry matter and stem dry matter, were 17,800; 17,077; 14,416; 13,594; 16,436; 12,361; and 18,149 plants ha-1 respectively. When adopting the planting density used by the farmers, a yield for marketable roots of 15,837 kg ha-1 was obtained. By using the optimal density as found in this work (13,594 plants ha-1), the yield was more than double that of the farmers. Increasing planting density reduced both the length of the marketable roots and the harvest index (the ratio of marketable-root dry matter to total plant dry matter). Na Mata Fresca, área situada na divisa dos Estados do Rio Grande do Norte e Ceará, pequenos agricultores têm como fonte de renda a obtida com a produ o de raízes de mandioca, usando densidades de plantio em torno de 5.000 plantas ha-1. Esse procedimento pode estar limitando a obten o de maiores rendimentos de raízes, pois alguns trabalhos demonstraram que é possível a obten o de rendimentos maiores da mandioca, com maiores densidades. O objetivo do trabalho foi avaliar o rendimento de raízes e outras características da mandioca em resposta à densidade de plantio. A cultivar Vermelhinha foi submetida às densidades de plantio de 5.000 a 21.000 plantas ha-1, com intervalos de 2.000 plantas ha-1, em experimento irrigado. Utilizou-se o delineamento de blocos completos casualizados com quatro repeti es. As densidades de plantios ideais para maximizar a obten o de matérias frescas de folhas, caule + ramos, total de raízes, de raízes comercializáveis, número de raízes comercializáveis, e de matérias secas de raízes comercializáveis e da parte aérea foram de 17.800; 17.077; 14.416; 13.594; 16.436;