Temporal variability and covariance structures of soil temperature in a sugarcane field under different management practices in southern Brazil

Extreme soil thermal regimes adversely affect soil functioning and reduce crop productivity. Thus, there is the need to understand the extent which soil tillage and mulching can modify extreme soil temperature conditions for optimum crop growth and productivity. The objective of this study was to investigate the residual effect of tillage and introduction of straw mulching on the temporal variability and covariance structures of soil temperature of a sugarcane field in southern Brazil during the 2011/2012 growing season. The experiment was laid out in a randomized complete block design (RCBD), with split-plot arrangement in three replications. The main treatment consisted of no tillage (NT), chiseling (Chi), compacted no tillage (NTC) and conventional tillage (CT) imposed a year before this study while the sub-plots (new treatments) were straw mulching and no mulching of previous sugarcane trash. Soil bulk density was determined at the middle of soil layers 0-10, 10-20, 20-40 and 40-60 cm using the core method. Soil water content (SWC) and temperature were monitored at the middle of soil layers,0-5, 5-10, 10-20, 20-40 and 40-60 cm, respectively in each treatment using TDR and copper-constantan sensors. Soil water content was measured manually while soil temperature data was recorded automatically every thirty (30) minutes. BD was highest (1.76 g cm(-3)) in the 10-20 cm layer of NTC treatment. SWC was lower in the surface layer of all tillage treatments, while straw mulch plots exhibited higher SWC values. Higher average, maximum, minimum and amplitude of soil surface temperature were observed in NTC and NT treatments. Straw mulching significantly influenced the soil thermal regime, as it suppressed the maximum soil surface temperature by 11 degrees C and the average daily temperature by about 4 degrees C during the critical summer period. During the critical winter season, daily average and maximum soil temperatures increased by about 3 and 4 degrees C by straw mulch, respectively. Straw mulching influenced temporal covariance structure of soil temperature. Applied statistical time series analysis of daily soil temperature used certain proportion of previous observations, gave higher coefficient of determination as well as being able to incorporate measurement and model errors, making it better than the corresponding classical linear regression procedure. This study showed that straw mulching could mitigate deleterious effects of supra-optimal temperature and protect the soil from sub-zero thermal conditions during the extreme summer and winter periods, respectively. (C) 2015 Elsevier B.V. All rights reserved.