Investigation of soil health and sustainable management in rice-based production systems

Interest in evaluating soil quality in agricultural systems has been developed since improper soil and crop management decisions can result in resource degradation, and subsequently detrimental changes in soil functions. A wide range of soil attributes including physical, chemical and biological properties were measured in the paddy fields of the Veneto region, Italy over the 2012 growing season (i.e. in April after field preparation, field moist condition; June mid-tillering, the early period of waterlogging; August panicle formation, the late period of waterlogging; October after harvesting, drained soil condition). The paddy soils were under four different rotation systems (rice-rice-rice: R-R-R; soya-rice-rice: S-R-R; fallow-rice: F-R; pea-soya-rice: P-S-R) and three replications. Soil quality was evaluated using three different soil quality indices, namely: an additive index, a weighted additive index and systematic soil quality index, by integrating indicator scores (linear and non-linear) obtained either by expert opinion or principal component analysis. Another part of field and laboratory experiments were conducted at the International Rice Research Institute, research farm in Los Baños, Philippines, to evaluate the effect of three rotation systems (i.e. flooded rice – non-flooded rice, flooded rice – flooded rice, flooded rice – maize) and four fertilizer treatments (i.e. conventional N management, no rice residues; zero N, no rice residues; conventional N management, with rice residues; zero N, with rice residues) on some soil indicators, in order to have a comparison between two different environmental conditions. All soil quality indices proved to be suitable for assessing the effects of various cropping patterns on soil functions. However, almost all SQ indices obtained based on the non-linearly scored PCA-MDS proved to be significantly better than the other SQ indices calculated by other methods in evaluating soil quality. The results of stepwise regression highlighted that extractable phosphorous (mg kg-1), β-glucosidase, and water filled pore space were the main factors limiting 2011-2012 rice yield when using the EO-MDSs as the independent variable, whereas the 2010 yield was strongly explained by the scored PCA-MDSs including AWC, Zn, CEC and chitinase. In general, for most indexing method combinations, P-S-R rotation received statistically higher SQI values than the other rotation systems. However, the results of systematic soil quality index based on non-linear scoring method showed that S-R-R yielded the highest SQI, followed by F-R, R-R-R and P-S-R. We suggest, therefore, that rice cultivation with alternating leguminous crops (e.g. pea, soybean) could result in higher overall soil quality than monoculture crop or fallow-rice rotation. Our observations associated with the results of paddy fields in IRRI indicated that both the cropping patterns and fertilizer treatments had a significant impact on the most measured soil quality indicators. It seems that flooded rice-flooded rice cropping systems and conventional N fertilizer management have a higher soil health condition than other treatments. Our experiments demonstrate that the best management practice should be selected based on environmental conditions and particularly climate. However, further indicators should be measured to calculate the soil quality index value in order to understand the real soil health condition in the study area.