Medium-term influence of conventional tillage on the physical quality of a Typic Fragiudult with hardsetting behavior cultivated with sugarcane under rainfed conditions

Abstract

Advances in soil science have enabled the development of different approaches for assessing soil physical quality related to sugarcane (Saccharum spp.) growth. The present study aimed to evaluate the medium-term influence of conventional tillage on the physical qualities of a Typic Fragiudult cultivated with sugarcane under rainfed conditions in the State of Pernambuco, northeastern Brazil. The experiment was conducted in a randomized block design with four replications. Each block was composed of two experimental units (plots), and two different tillage systems were tested: i) minimum tillage (MT) (i.e., furrowed plots) and ii) conventional tillage (i.e., chiseled, harrowed and furrowed plots). The following soil physical attributes were determined in the laboratory: bulk density, wet aggregate stability and size distribution, total porosity and pore-size distribution and saturated hydraulic conductivity; both soil water retention and penetration resistance curves also were constructed. Soil penetration resistance in the field was also determined. To obtain a better understanding of these systems, we calculated the following soil quality indicators based on our laboratory data: least limiting water range, integral water capacity and integral energy; we also calculated the S and H indexes. Furthermore, sugarcane productivity and quality were assessed. After 17 months, no evidence was obtained indicating that conventional tillage improved some structural properties of the soil, including bulk density and aggregation. On the other hand, conventional tillage increased total porosity and modified pore-size distribution. Thus, CT increased slightly the total porosity of the soil by 2.1% and as result PR values reduced around 30% at 15-20 cm depth. Consequently, there was an increase in soil hydraulic conductivity, which reduced storage capacity, increasing the hardsetting behavior but without compromising the water availability for sugarcane at the surface layer (0–30 cm). On the other hand, conventional tillage increased the least limiting water range, but this increase was not enough to indicate good physical quality, mainly due to restrictions by penetration resistance. The integral energy values were similar between tillage systems. With respect to the crop, the conventional tillage system neither improved productivity nor quality. We concluded that conventional tillage improved the physical quality of a Typic Fragiudult in the medium term. However, under rainfed conditions, stalks and sugar yields depend on rainfall amounts and distribution rather than on the applied tillage system.