The soil tillage for potato in Brazil commonly relies on harrow utilization (shallow tillage), which causes a compacted zone below 20 cm. Apparently, deep soil loosening improves productivity and reduces tuber disease incidence and these effects can vary according to the species of grass cultivated before the potato crop. The objective of this work was to study deep loosening associated to the cultivation of Panicum maximum cv. Tanzânia, Brachiaria brizantha cv. Marandu and maize (Zea mays) 'Dekalb 191' and the control (shallow tillage with the same maize genotype). The experiment was carried out in Piracicaba, São Paulo State, Brazil, from December 2006 to October 2008, in a complete randomized blocks design. The soil penetration resistance (SPR) value, evaluated by impact penetrometer in the center of the seed bed, was lower than 1.5 MPa up to 40 cm depth for all treatments and, in the 40-60 cm layer, the SPR value in the shallow tillage (2.4 MPa) was statistically higher than all other treatments, whose values ranged from 0.9 to 1.0 MPa. Tuber productivity in the shallow tillage was 28.3 t ha-1 and differed from the highest value among the deep soil loosening treatments (32.9 t ha-1). The proportion of tubers with less than 4 cm diameter in the shallow tillage (5.1%) was higher than the deep soil alleviation treatments with maize (2.9%) and B. brizantha (2.2%). The occurrence of tuber pests, diseases and lenticelose (Diabrotica speciosa, 31.0% to 49.7%; Streptomyces scabies, 3.3% to 6.3%; Helminthosporium solani, 60.3% to 69%; Rhizoctonia solani, 1.3% to 4.3%; lenticelose, 6.0% to 15.7%), was not influenced by the treatments. The deep soil loosening reduced soil penetration resistance and increased potato productivity, with lower rate of small tubers, but did not affect the occurrence of tuber pests, diseases and lenticelose.
Solanum tuberosum; previous grass crop; disease; soil management
