Annual crop rotation of tropical pastures with no-till soil as affectedby lime surface application.

Soil acidity and low natural fertility are the main limiting factors for grain production in tropical regionssuch as the Brazilian Cerrado. The application of lime to the surface of no-till soil can improve plant nutrition, dry matter production, crop yields and revenue. The present study, conducted at the Lageado Experimental Farm in Botucatu, State of São Paulo, Brazil, is part of an ongoing research project initi-ated in 2002 to evaluate the long-term effects of the surface application of lime on the soil?s chemical attributes, nutrition and kernel/grain yield of peanut (Arachis hypogaea), white oat (Avena sativa L.) and maize (Zea mays L.) inter cropped with palisade grass (Urochloa brizantha cv. Marandu), as well as the forage dry matter yield of palisade grass in winter/spring, its crude protein concentration, estimated meat production, and revenue in a tropical region with a dry winter during four growing seasons. The experiment was designed in randomized blocks with four replications. The treatments consisted of four rates of lime application (0, 1000, 2000 and 4000 kg ha−1), performed in November 2004. The surface application of limestone to the studied tropical no-till soil was efficient in reducing soil acidity from the surface down to a depth of 0.60 m and resulted in greater availability of P and K at the soil surface. Ca and Mg availability in the soil also increased with the lime application rate, up to a depth of 0.60 m. Nutrient absorption was enhanced with liming, especially regarding the nutrient uptake of K, Ca and Mg by plants.Significant increases in the yield components and kernel/grain yields of peanut, white oat and maize were obtained through the surface application of limestone. The lime rates estimated to achieve the maximum grain yield, especially in white oat and maize, were very close to the rates necessary to increase the base saturation of a soil sample collected at a depth of 0?0.20 m to 70%, indicating that the surface liming of 2000 kg ha−1is effective for the studied tropical no-till soil. This lime rate also increases the forage dry matter yield, crude protein concentration and estimated meat production during winter/spring in the maize-palisade grass inter cropping, provides the highest total and mean net profit during the four growing seasons, and can improve the long-term sustainability of tropical agriculture in the Brazilian Cerrado.

Straw and early nitrogen fertilization affect soil properties and upland rice yield.

The presence of cover crop straw and early application of total N at sowing may provide significant changes in the microbial population, reflecting on the N dynamics in the soil and in upland rice plants. This study aimed at determining the effect of the early application of nitrogen doses as mineral N and microbial biomass carbon in the soil, as well as in the activity of nitrate reductase, and grain yield of upland rice plants cultivated under notillage system (NTS). A randomized blocks design, in a split-plot scheme, with four replications, was used. The treatments consisted of N doses (0 kg ha-1, 40 kg ha-1, 80 kg ha-1 and 120 kg ha-1) and the presence or absence of U. brizantha cover straw. Maintaining the straw on the soil surface reduces the ammonium levels and increases the microbial biomass carbon content of the soil. The application of increasing doses of N in the soil provides increases in the levels of nitrate and ammonium in the soil up to 28 days after emergence. The activity of the nitrate reductase enzyme in the plants increases and the contents of ammonium and nitrate in the soil decrease with the crop development. The number of panicles and grain yield of upland rice increase with the increase of the nitrogen fertilization, but decrease in the presence of U. brizantha straw. Thus, it is recommend the use of early N fertilization in upland rice crop.

Relationships between labile soil organic carbon fractions under different soil management systems.

ABSTRACT: The study of labile carbon fractions (LCF) provides an understanding of the behavior of soil organic matter (SOM) under different soil management systems and cover crops. The aim of this study was to assess the effect of different soil management systems with respect to tillage, cover crop and phosphate fertilization on the amount of the LCF of SOM. Treatments consisted of conventional tillage (CT) and no-tillage (NT) with millet as the cover crop and a no-tillage system with velvet bean at two phosphorus dosages. Soil samples were collected and analyzed for organic carbon (OC), C oxidizable by KMnO4 (C-KMnO4), particulate OC (POC), microbial biomass carbon and light SOM in the 0.0-0.05, 0.05-0.10 and 0.10-0.20 m soil layers. The Carbon Management Index (CMI) was calculated to evaluate the impacts of soil management treatments on the quality of the SOM. The different LCFs are sensitive to different soil management systems, and there are significant correlations between them. C-KMnO4 is considered the best indicator of OC carbon lability. In the soil surface layers, the CT reduced the carbon content in all of the labile fractions of the SOM. The use of phosphorus led to the accumulation of OC and carbon in the different soil fractions regardless of the tillage system or cover crop. The application of phosphate fertilizer improved the ability of the NTsystem to promote soil quality, as assessed by the CMI.

Assessment of sugarcane harvesting residue effects on soil spectral behavior

When the harvesting of sugarcane involves a mechanized process, plant residues remain on the soil surface, which makes proximal and remote sensing difficult to monitor. This study aimed to evaluate, under laboratory conditions, differences in the soil spectral behavior of surface layers Quartzipsamment and Hapludox soil classes due to increasing levels of sugarcane?s dry (DL) and green (GL) leaf cover on the soil. Soil cover was quantified by supervised classification of the digital images (photography) taken of the treatments. The spectral reflectance of the samples was obtained using the FieldSpec Pro (350 to 2500 nm). TM-Landsat bands were simulated and the Normalized Difference Vegetation Index (NDVI) and soil line were also determined. Soil cover ranged from 0 to 89 % for DL and 0 to 80 % for GL. Dry leaf covering affected the features of the following soil constituents: iron oxides (480, 530 and 900 nm) and kaolinite (2200 nm). Water absorption (1400 and 1900 nm) and chlorophyll (670 nm) were determinant in differentiating between bare soil and GL covering. Bands 3 and 4 and NDVI showed pronounced variations as regards differences in soil cover percentage for both DL and GL. The soil line allowed for discrimination of the bare soil from the covered soil (DL and GL). High resolution sensors from about 50 % of the DL or GL covering are expected to reveal differences in soil spectral behavior. Above this coverage percentage, soil assessment by remote sensing is impaired.

Strategies to enhance the productivity of rainfed off-season maize.

In Brazil, off-season rainfed maize is usually affected by limited water due to irregularities in rainfall. Alternatives to mitigate these effects include ground cover to reduce evaporation losses and the use of cultivars with a deeper rooting system. We conducted a study in Goias, Brazil, to evaluate the influence of different crop management strategies to mitigate the effect of limited water in maize yield. Modeling was used to simulate scenarios that consisted of 0, 3.5 and 5.0 t ha-1 of soybean residue left on the soil surface combined with cultivar ideotypes with 0.30 m, 0.50 m 0.70 m deep rooting system grown with 60 and 340 kg ha-1of nitrogen. The results showed that maintaining residue in the soil surface in combination with the use of cultivars with deeper rooting systems favored higher yields of off-season maize. Our results also indicated that a cultivar with rooting system in the top 0.50 m of the soil fertilized with a high nitrogen rate tended to be more efficient in the use of the soil available water

Modeling nitrous oxide emissions in grass and grass-legume pastures in the western Brazilian Amazon.

Mineral nitrogen (N) dynamics in soil and the exchange of N gaseous in the interface soil-atmosphere are intimately associated with animal manure in pastures. According to soil inorganic-N pools and the site studied, forest or pasture, and pastures age the soil inorganic-N pools of ammonium and nitrate can be similar in the forest or ammonium dominated in the pasture. Also annual average net nitrification rates at soil surface in forest can be higher than in pasture suggesting a higher potential for nitrate-N losses either through leaching or gaseous emissions from intact forests compared with established pastures (NEILL et al., 1995).

Spatial variability of soil properties and yield of a grazed alfalfa pasture in Brazil.

2016

Spatial variability of satured soil hydraulic conductivity in the region of Araguaia River - Brazil.

This study evaluates the spatial variability of saturated hydraulic conductivity in the soil in an area of 51,850 ha at the headwaters of the Araguaia River MT/GO. This area is highly vulnerable because it is a location of recharging through natural water infiltration of the Guarani Aquifer System and an area of intense increases in agriculture since its adoption by growers in the last 30 years. Soil samples were collected at 383 points, geographically located by GPS. The samples were collected from depths of 0 - 20 cm and 60 - 80 cm. Exploratory statistics and box-plot were used in the descriptive analysis and semivariogram were constructed to determine the spatial model. The exploratory analysis showed that the mean hydraulic conductivity in the superficial layer was less than at the level of 60-80 cm; however, the greatest variability evaluated with a coefficient of variation also was from this layer. Data tended towards a normal distribution. These results can be explained by the greater soil compaction in the superficial layer. The semivariogram models, adjusted for the two layers, were exponential and demonstrated moderate and strong dependence, with ranges of 5000 and 3000 utm respectively. It was concluded that soil use is influencing the spatial distribution model of the hydraulic conductivity in the region.

Spatial variability of satured soil hydraulic conductivity in the region of Araguaia River - Brazil.

2008