Atributos químicos, físicos e agronômicos de cana-soca submetida a níveis de palhiço

Abstract

The advantages obtained with the chaff as ground cover have been reported by many researches, however what quantity would be sufficient to obtain improvements for culture were not exactly defined. The amount of chaff which maximizes the benefits to the ground and the culture is paramount importance information, once it will determine the amount to remain in the field, the volume that can be used in other sectors such as cogeneration bioelectricity and production of second generation bioethanol, thus obtaining the maximum conversion efficiency of the solar sugarcane. This way, the aim of this study was to evaluate the development of regrowth and productivity of sugarcane underwent to chaff levels above the ground; the mechanical action of swather in working speeds to harvest time; the effects of straw levels on chemical and physical attributes of an Oxisol Haplorthox at harvest time. The experimental area was carried out in Dourados, MS, with third cut cane ratoon, at times 1 (variety RB 855156, early cycle), time 2 (variety RB 835486, average cycle) and time 3 (variety RB 835054 late cycle) . At each harvest time promoted bunching up of the residual straw in four operating speeds (0 (manual); 7.1; 9.7; 11.6 and 14.2 km h-1) and kept on ground four levels of straw (0, 5, 10 and 15 Mg ha-1). It was evaluated plant height, number of stems, stem diameter, productivity (TCH) and technical analysis (Brix, sugarcane AR, Pol cane and ATR). The soil samples for chemical attributes were collected in all experimental parcels at depths of 0-5; 5-10; 10-20 cm, the undisturbed soil samples to assess the physical attributes of soil were collected at depths of 0-5; 5-10; 10-15 and 15-20 cm, and soil penetration resistance up to 40 cm depth, after the harvest of sugarcane in 2012, before the establishment of straw levels (initial) and after harvest of ratoon crop in 2013 (final), occurred after 12, 12 and 9.5 months in the times 1, 2 and 3, respectively. For chemical attributes were analyzed pH levels (CaCl2), calcium (Ca ++), magnesium (Mg ++), phosphorus (P) available changeable potassium (K), based saturation (%) and organic matter (OM) and soil physical properties the following determinations were performed: density, macro and microporosity of the soil, total porosity and soil resistance to penetration. The chaff levels did not influence the production of stems in the early and half harvest crop and in the final crop was obtained maximum production of stems with maintaining 5 Mg ha-1 of straw. There was no effect of raking speeds in the harvest of early harvest, the crop through crop yielded higher yields of stems in windrowing speeds of 7.1 and 14.2 km h-1, and the final harvest crop at the speed of 14.2 km h-1. The production of cane sugar per hectare is not changed depending on the straw levels and speeds of windrowing the straw. The partial payment of straw held only once, did not promote reduction in the production of sugars per unit area in the next harvest. The windrowing of straw at speeds up to 14.2 km h-1, provide greater operational capacity, without reduction in the production of stems and sugars in a crop. There was no significant increase in the levels of the evaluated nutrients in the topsoil, after a year from planting, even with the maintenance of 15 Mg ha-1 of chaff and there was no increase in the amount of organic matter evaluated in the topsoil after a year of cultivation, even with the total gathering straw, regardless of the age of the cane harvest. This way it is suggested the possibility of performing the partial gathering of straw for other uses without affecting the soil chemical attributes, in the following harvest. For the three periods evaluated, the parcels with straw waste spread on the surface of the soil by mechanical harvesting of raw cane occurred a reduction in density, microporosity and total soil porosity and increased soil macroporosity, after a year of assessment. Soil density values were high, but without hindering the growth of the plant; the three harvest times and in all evaluated straw levels. The amount of vegetable waste spread on the soil surface did not differ for the soil resistance to penetration, after a year of assessment.