Efeito do manejo da colheita e do sistema de cultivo sobre atributos edáficos de Argissolo Amarelo e produtividade de cana soca em Linhares (ES)

Abstract

The Brazil is placed in the world rank of sugarcane production as the largest producer of ethanol and sugar. Thus, the need to meet the demand for raw materials has instigated the search for more productive and sustainable over time systems. In this sense, the stubble management system before the harvest of the sugarcane fields is a key factor; where burning cane (manual harvesting) is being substituted by the no-burning (generally with mechanical harvesting) also named green cane, in the sugar and alcohol sector. This is motivated by legal, economic and mainly environment aspects. However, more intense traffic of machinery and implements in the mechanical harvesting system may influence the choice of tillage system, when renewing the cane fields, one of the phases that most influence the production costs. This study had as objectives to evaluate, in the Chapter I, the effect of two tillage systems (minimum and conventional) associated with two straw managements (with and without burning) on the soil chemical and physical properties; in the nutrient uptake by different aerial parts of the crop and in sugarcane yield; and if the managements systems influenced the soil phosphorus fractions. Also in the Chapter II, to evaluate the same variables in Chapter I, but with different treatments, that was the maintenance, alternation and absence of burning before the cane harvesting in the crop cycles. Two cane management long-term experiments were used, implemented in 1989, in an area of LASA distillery, located in municipality of Linhares - ES. The soil is an Udult with sandy over medium texture, typical of the coastal tableland environment. The sugarcane (Saccharum spp.) variety was the SP79-1011, and the soil and plants samples were taken in 2012, during the seventh production season (6th ratoon) harvesting of the third cycle of cultivation, for both experiments. In the Chapter I, results indicated that systems of tillage and straw management of sugarcane did not significantly affect the biomass production and the technological parameters. However, the minimum tillage system favored the maintaining of carbon of the humic fractions and carbon associated to minerals, in the 0-10 cm soil layer; the values of Mg+2, Ca+2 and total organic carbon in all evaluated layers; the K+ level for the 10-20 cm layer; and the weighted mean diameter (PMD) and geometric mean diameter (GMD) in the two subsurface layers, when compared to conventional tillage. On the other hand, there were higher values of macroporosity and total pores than the minimum tillage, which was reflected in the plants biomass production. Results in the Chapter 2 showed that the straw management systems influenced mostly the accumulation of nitrogen and potassium on the cane pointers. However, the soil chemical and physical attributes were not affected significantly. Thus, it is concluded that the soil tillage contributed more for changes in soil chemical and physical properties than the straw management. Regarding the distribution of phosphorus (P) fractions according to their lability, in both experiments (Chapter I and II), majority of P was in the inorganic form, and the moderately labile P comprised the largest proportion of the total soil P, when compared the labile and moderately resistant P fractions.