Regularidade de resposta da cultura do milho à compactação do solo

Abstract

The hypothesis that soil compaction in no-tillage affects crop production has been tested often, however, there is no regularity in the relationship between plant response and soil compaction indexes that has allowed generalization of research results. Therefore the objective of this study is to investigate these relationships. An experiment was conducted on an Oxisol under eight corn crops grown (Zea Mays L.) during the 2010/2011 and 2011/2012 growing seasons using no-tillage (NT), no-tillage + chiseling (CNT) and no-tillage + traffic (TNT) treatments. The aim of additional chiseling and traffic is to reduce and increase soil compaction, respectively. From the soil physical properties and daily sequential water balance, soil indexes were calculated over the entire corn cycle in NT, CNT and TNT, consisting of frequencies and accumulated resistance to penetration (RP), matric tension (ψ) and fraction of available water (FAW). Other soil indexes were calculated, including the frequency that the water content (θ) remained of the least limiting water range (LLWR) and the LLWR amplitude, using different values of ψ and RP in the lower limits of the LLWR. Agronomic parameters measured include: plant height (Ph), leaf area index (LAI), effective rooting depth (Rd) and grain yield. Correlation and regression analyzes were performed to assess the relationship between measures of corn and soil indexes. The soil indexes regularly indicated that the increase in compaction decreased Ph, LAI and Rd. Grain yield ranged from 1980 to 5738 kg ha-1 in the eight corn crops, but there was little statistical evidence that this variability was caused by compaction. The corn variables were weakly correlated with ψ and FAW. Alone, RP was more efficient than the IHO to relate response of corn to soil compaction, and the RP efficiency increased when RP was subject to decay with decreasing in θ. However, the most efficient RP index explained only 25, 24 and 6% of the variation in Ph, LAI and grain yield, respectively. Furthermore, the assumption that the LLWR indicates soil physical quality for crop production was statistically refuted by grain yield. The evidence from this study indicate that soil physical indexes such as LLWR, critical density and penetration resistance are inefficient to investigate the regularity of plant response to soil compaction.