Abstract
This study was conducted at the Experimental Station belonging to UNESP Engineering University, Ilha Solteira Campus, based in Selviria, Mato Grosso do Sul State, Brazil, with the aim of evaluating chemical alterations in an Oxisol after being managed for two years with organic and/or chemical fertilization and different tillage systems during the agricultural years of 2004/2005 and 2005/2006. The treatments were: conventional-tillage; chisel tillage and no-tillage; the fertilization treatments were: control (no fertilization); chemical fertilization (300 kg ha -1 from the 20-00-20); organic fertilization (cattle manure - 20 Mg ha -1 ); organic + ½ the recommended chemical fertilization for the used crop; 20 and 30 Mg ha -1 of sewage sludge. Soybean was used in the first year and sorghum in the next year, evaluating the soil chemical attributes in four layers. The soil chemical attributes were changed in the first year; the organic fertilization, sewage sludge and organic+chemical fertilization were efficient to change the chemical attributes; the sewage sludge was more efficient in soil P recuperation and, the no-tillage system contributed to soil K increase.
Highlights
Savannah soils usually provide low yields due to the high Al saturation, low contents of most of the mineral nutrients that are essential to the plants development, low organic matter content, leading to low CEC and high phosphorus fixation (FAQUIN et al, 2000)
Its application in order to increase soil P up to very high contents must be carefully performed in areas where there is surface drainage, as it could lead to the contamination of water courses (TRANNIN et al, 2005)
As for the pH, it was observed that the sewage sludge treatments provided the lowest numbers not differing from the chemical and organic fertilization treatments (Table 3)
Summary
Savannah soils usually provide low yields due to the high Al saturation, low contents of most of the mineral nutrients that are essential to the plants development, low organic matter content, leading to low CEC and high phosphorus fixation (FAQUIN et al, 2000). Sewage sludge usually contains low potassium content due to the obtaining process, the opposite of what happens to phosphorus, which is present in a high content and, most importantly, approximately 80% of it is available in the first application year (SIMONETE et al, 2003) Another important factor is the sewage sludge decomposition in the soil which allows a better uptake of the nutrients by the plants as they are slowly released via the organic matter mineralization process (DEBOSZ et al, 2002). Nascimento et al (2004), evaluating the chemical changes in a soil under corn and beans crops where sewage sludge was used, observed an increase in the organic matter, total nitrogen, phosphorus, sodium, calcium and magnesium contents though potassium and sodium contents were not altered. Based on what was mentioned, this research work had the objective of studying the changes in the chemical attributes of a Typic Hapludox in a savannah in Mato Grosso do Sul State, after two years under different tillage systems and managements with organic and/or chemical fertilization
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