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IWRA World Water Congress 2008 Montpellier France
5. Water Governance and Water Security
Author(s): Joao Carlos Cury Saad
Marcelo Augusto De Aguiar E Silva
Leonardo Pretto De Azevedo
Professor, Agricultural Science School, São Paulo State University, Rua José Barbosa de Barros, 1780, Botucatu, SP, 18610-307, Brazil; joaosaad@fca.unesp.br

Keyword(s): rational use of water, irrigation, soil management

AbstractCurrently the demand for water resources has increasing as a result of population pressure and industrial developments. In Brazil, about 70% of the available water resources are used for agriculture purposes. The adoption of rational techniques for soil and water conservationist management is vital for sustainability so that these resources will be preserved along time with sufficient quantity and quality for the maintenance of satisfactory productivity levels in agriculture. The conventional soil management has been successfully replaced in many agricultural regions worldwide and particularly in Brazil. In the last decades, the quick degradation of soil under agricultural exploitation worldwide, especially in tropical developing countries has arisen the concern on soil quality and sustainability of the agricultural exploitation. The no- tillage system presents as main characteristic the implementation of culture without drastic soil mobilization, in other words, without its preparation or mobilization before sowing, the mobilization occurs only at the sowing line. This type of system also involves the maintenance of vegetal residues from previous cultures at its surface and the diversification of species through culture rotation. The maintenance of residues at the soil surface in the no-tillage system, besides the increase on the water retention, also has a great potential to reduce irrigation water requirement. The objective of this work was to evaluate how two different soil management systems, conventional and no- tillage, influence the soil water retention, irrigation water requirement, compaction, root development and bean yield irrigated by center pivot system. The study was conducted at the farm of an irrigating producer in the largest irrigated region of the state of São Paulo, Brazil, during the second semester of 2003. The culture selected was bean cultivar Rubi, which sowing occurred at August 02 and harvest at November 25, summing up 116 days of culture cycle. The experimental design was fully randomized with two treatments and 13 repetitions. The experimental parcels were placed under an 18 ha central pivot and divided into two soil management types: conventional and no-tillage. The conventional management was performed by means of the use of plow and grid, while the no-tillage was characterized by sowing performed under remainders of the previous culture with no soil revolving and it does not characterize a continuous no-tillage system, once operations such as soil preparation aimed at eliminating the cotton stump and subsoiling for the elimination of compacted soil layers and redistribution of nutrients along the soil profile are periodically perform. Although no-tillage management presented higher water retention and lower compaction at the most superficial soil layers as well as more uniform root distribution in the soil profile, the soil managements did not present significant differences in relation to crop productivity. It was verified that the no-tillage management generated indirect benefits like reduction in the irrigation water requirement. Since conservationist management cycles are short, time was not enough to promote structural changes in the soil and hence significant alterations in the physical-hydric properties that would lead to higher root development and crop yield.
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