Soil and water losses along the cultivation cycle of onion in Irati, Brazil

Onion is one of the most important vegetables grown in southern Brazil. However, despite its profitability, little is known about its response to soil erosion throughout its productive cycle divided into 5 stages: S1 (germination), S2 (formation of leaves and roots), S3 (bulbification), S4 (snap) and S5 (harvesting). With the aim of providing knowledge in this matter we have analyzed the intra-cycle dynamics of some parameters such as bulk density (BD), porosity, soil penetration resistance (SPR), and soil and water losses. To do that we have assessed these parameters in 40 random points and at different depths in a representative farm of 3 ha located in the municipality of Irati (Paran'a, Brazil). BD was quantified by using the core method, porosity after particle density quantification by the volumetric balloon method, and SPR by impact penetrometer. Soil and water losses were estimated after carrying out 30 rainfall simulations (6 per crop stage). The results showed that bulk density increased progressively and continuously from 1.06 to 1.36 g cm(-3). This greater compaction was also observed in the values of SPR that increased from 2.0 to above 3.0 MPa at the end of the cycle. Regarding soil erosion the highest rates were recorded at S4 when onions are snapped (431.0 g m(-2)). We conclude the occurrence of runoff and soil erosion is a consequence of the increase in soil compaction throughout the cycle provoked by the repeated pass of heavy machinery and workers to apply herbicides and fertilizers. Since soil erosion rates found are relatively high (1437.1 g m(-2) y(-1)) we suggest the progressive implementation of conservationist practices to guarantee its sustainability.