Friday, 14 July 2006

Soil Quality Assessment of Rice Production Systems in South of Brazil.

A.C. Rodrigues de Lima1, W.B. Hoogmoed1, and Lijbert Brussaard2. (1) Wageningen University, Farm Technology Group, P.O. Box 17, 6700 AA, Dept. of Soil Quality, P.O. Box 8005, 6700 EC, Wageningen, Netherlands, (2) Wageningen University and Research Centre, Dept. Soil Quality, P.O. Box 8005, 6700 EC, Wageningen, Netherlands

Soil quality as a measure of the capacity of soil to function can be quantified by indicators based on physical, chemical and biological properties. Measuring key soil quality indicators over a period of time allows evaluating changes in soil quality resulting from various management systems. So, the assessment of soil quality is a primary indicator of sustainable management. Several Minimum Data Set (MDS) of soil attributes have been proposed for use as soil quality indicators at the plot and field scale, at a regional scale and national scale. Currently, there is no consensus on a definitive data set for soil-quality monitoring, or how the indicators should be interpreted. This can partly be explained by the fact that monitoring is site specific; depending on purpose of the land use and different soil conditions are desirable. In the state of Rio Grande do Sul, Brasil, rice production is one of the most important agricultural activities in the region. This production is located mainly in the southern lowlands yielding approximately 5,5 million tons of rice per year, equivalent to 52% of total Brazilian rice production. In this region, soil degradation is observed, but maintaining soil quality at a desirable level is a very complex issue due to the nature of the current production systems involving intensive tillage. The study presented here was conducted with the following objectives: (i) to identify the most significant soil quality factors from a set of measured soil indicators following a comparative approach (in which the performance of the management system is determined in relations to alternatives at a given time only), (ii) to test whether this dataset can discriminate between management systems or soil classes in order to establish regional minimum data set (MDS). It was hypothesized that, because of the inherent differences in clay content in the soils in the region, the intensive anthropic activities (management systems) cannot be the only explanation of differences in soil quality indicators. For this study, soil biological (microbial biomass, soil respiration, potentially mineralizable N, ß-glicosidase, acid phosphatase, alkaline phosphatase, microbial biomass), chemical (organic matter, total N, pH, Al, H+Al, Al saturation, Ca, Mg, K, P, Iron, Zn, Cu, Mn and Cation exchange capacity) and physical (Bulk density, texture, water stable aggregate, microporosity and water content) indicators were evaluated. Some additional indicators were derived from the data set such as available water, macroporosity, mean weight diameter, microbial quotient. A total number of 29 indicators were analized. Data were collected from 21 rice fields located in the Camaquć region of Rio Grande do Sul that were under the three main soil management systems : Conventional, Pre-Germinated and Semi-direct. In total 105 representative points were sampled. Multivariate analysis was used for establishing the MDS. Different MDS were found when either the management systems or the soil classes were considered in the analysis. This study is a first step toward identifying how the MDS can be meaningfully applied to monitor soil quality of rice fields in South of Brazil. Keywords: Soil quality; indicators; minimum data set; rice; Brazil.

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