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Soil preparation may break its structure, destabilize the aggregates, and cause the loss of organic matter (OM). The study of spatial variability of soil attributes is an important indicator of soil physical quality. The aim of this study was to describe the spatial variability of the stability of aggregates and organic matter in Oxisol (Yellow Latosol) under different management systems.We collected simple samplings of soil in the eastern mesoregion of Maranhão, Brazil. Experimental areas with two distinct management systems were studied: conventional tillage and no-tillage. In each experimental area, we fitted a rectangular mesh of 50 points with 40m of spacing and 0.00 to 0.20 mof depth. The response variables were: weighted mean diameter (WMD); geometric mean diameter (GMD); percentage of aggregates (on classes of size between 1-2 mm and above 2 mm); and organic matter (OM). The no-tillage management showed high values of WMD, GMD, class of aggregates and OM. Maps of WMD and GMD were spatially correlated to OM map at no-tillage management. Soil properties had a spatial-dependent structure. The management system influenced the stability of aggregates and the amount of organic matter.

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The objective of this work was to assess the physicochemical and microbiological characteristics, as well as the potential of salinization and sodification of groundwater wells in Limoeiro do Norte, Ceará states, Brazil. Six water wells were selected for the study, all of them used for irrigation and human consumption. The ionic classification was performed by Piper Diagram and the salinity risk using the U.S.S.L. (United States Salinity Laboratory) Diagram using Qualigraf software. Based on the average chemical element concentration (mmolc L-1) in the groundwater, the following quantification is obtained: Na+ > Ca2+ > Mg2+ > K+ for cations. For anions there was a change in the the wells, for the 1, 3 and 4 Cl- > HCO3- > SO42- > CO32- and wells 2, 5 and 6 HCO3- > Cl- > SO42- > CO32-. The wells 1, 2 and 3 have severe restrictions for use by SAR (sodium absorption ratio) and Na+ content. Water from wells 1, 3 and 5 were classified as sodium chloride, 2 and 6 were classified as sodium bicarbonate and well 4 as calcium magnesium sulfate. With the exception of well 6 classified as freshwater, all other wells were classified as brackish water. Groundwater samples fall in C3S1 or C3S2 category with high salinity and low or medium sodium hazard. With the exception of Na+, whose value was above the limit allowed, no well with groundwater was detected chemical hazard for human consumption. There was the detection of Total coliforms, but in well 5 the presence of Thermotolerant coliforms was detected.

This work summarizes information about organic nitrogen (N) in the agricultural system. The organic N forms in soils have been studied by identifying and quantifying the released organic compounds when soils are acid treated at high temperature, in which the following organic N fractions are obtained: hydrolyzable total N, subdivided into hydrolyzable NH 4 + -N, amino sugars-N, amino acids-N, and unidentified-N and acid insoluble N, a fraction that remains associated with soil minerals after acid hydrolysis. Nitrogen mineralization and immobilization are biochemical processes in nature. This chapter summarizes how these processes occur in the agricultural system. Then, soluble organic nitrogen (SON), volatilization and denitrification processes, and biological nitrogen fixation (BNF) as a key component of the nitrogen cycle and how it makes N available to plants are also discussed. Finally, we discuss the use of organic fertilizers as N source to satisfy the worldwide demand for organic foods produced without synthetic inputs.