Effects Of Conservation Agriculture On Osil Macrofauna And C And N Levels In The Cerrado Of Brazil

Author : Tilman E. Renz
Publisher :
ISBN 13 :
Total Pages : 144 pages
Book Rating : 4.:/5 (634 download)

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Download or read book Influence of Land Use on Microbial Parameters and Phosphatase Activity in Cerrado Oxisols written by Tilman E. Renz and published by . This book was released on 1997 with total page 144 pages. Available in PDF, EPUB and Kindle. Book excerpt: Agriculture and cattle ranching in the Cerrado affect the organic matter of its soils. Soil microbial biomass is considered a more sensitive indicator for organic matter dynamics than total C, and potential phosphatase activity was shown to often be closely linked to soil P, which is the limiting element for plant growth in this savanna. The main objective of this study was to evaluate the effects of land use on microbial biomass, microbial activity and acid monophosphatase activity in Cerrado Oxisols. The possibility of using these parameters as indicators of soil organic matter dynamics and the soil's P mineralization capacity, respectively, was assessed. By analyzing the distribution of microbes and phosphatases in core and shell of large macroaggregates, an attempt was made to include soil structure in the considerations. A Pinus reforestation, a no-till as well as a tilled crop field, three established pastures and in part of the study a pasture after crop, i.e. planted on a former field were compared with native Cerrado on a clayey Oxisol. For a loamy Oxisol, an arable field, a degraded pasture and again native Cerrado were included. Soil microbial carbon (Cmic) and potential acid monophosphatase activity were measured. For analysis of microbial activity, the dimethyl sulfoxide reduction method was carbon (WEOC) as well as NaOH-extractable organic and inorganic P (NaOH-P and NaOH-Pi). Large macroaggregates of clayey pastures, the clayey no-till crop and the clayey Cerrado were separated into core and shell and analyzed for the same parameters as the bulk soil with the exception of Cmi and WEOC. In addition, for those samples a sequential Hedley-P-fractionation was performed. For all parameters other than pH, values were higher in the clayey than in the loamy soil. Land use was found to highly affect soil microbiology: Cultivation of maize as reforestation with Pinus reduced Cmic, microbial activity and phosphatase activity in comparison to the native Cerrado. Termination of tillage seemend to at least in the topsoil slightly diminish cultivation effects on Cmic and activity parameters. The establishment of pasture on the clayey soil did not have negative consequences on Cmic and even stimulated microbial as well as phosphatase activity. The pasture after crop slowed to have rapidly recovered from cultivation in regard to phosphatase activity, microbial activity, C and N. On the other hand it had to a large extent retained the high NaOH-Pi level found in fertilized crops. Microbial C was highthy correlated with all parameters other than pH, indicating its close relationship to soil organic matter. Root distribution as weell as organic matter input were considered to be major factors determining Cmic, which was proposed to be C-limited in the clayey crops and possibly N-limited in the clayey pastures. Soil structure was found to be another important parameter in regard to Cmic, since core-shell separation revealed that microbes and enzymes accumulated in cores of large macroaggregates, which may be destroyd by land management. Phosphatase was highly related to microbial vitality of the soil and therefore also depended much more on soil organic matter and soil structure than on P levels analyzed. This implies a rather low P supply of the microbes, which evidently produced the enzyme dependent on their C supply and P demand, but independently of available Pi levels. Altogether, it was confirmed that biomass can be considered highly sensitive to land use also in the Cerrado, and the Cmic/C quotient is suggested as an indicator of organic matter dynamics. Potential phosphatase activity may be useful as an indicator of a soil's P mineralization capacity, but it cannot serve to evaluate actual P mineralization rates of the given soils. Nevertheless, in connection with findings for microbial activity and inorganic P, it indicates a lack of microbially avaibable phosphate, which implies a possibly strong competition of plants and microorganisms for this element.