Nitrogen Supply for Cover Crops and Effects on Peanut Grown in Succession under a No-Till System

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Least limiting water range in soil under crop rotations and chiseling

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Soil Solution as Affected by Plant Residues and Nitrogen Rates

Cation mobility in acidic soils with low organic-matter contents depends not only on sorption intensity but also on the solubility of the species present in soil solution. In general, the following leaching gradient is observed: potassium (K+) magnesium (Mg2+) calcium (Ca2+) aluminum (Al3+). To minimize nutrient losses and ameliorate the subsoil, soil solution must be changed, favoring higher mobility of M2+ (metal ions) forms. This would be theoretically possible if plant residues were kept on the soil surface. An experiment was conducted in pots containing a Distroferric Red Latosol, with soil solution extractors installed at two depths. Pearl millet, black oat, and oilseed radish residues were laid on the soil surface, and nitrogen (as ammonium nitrate) was applied at rates ranging from 0 to 150mgkg-1. Corn was grown for 52 days. Except for K+ and ammonium (NH4 +), nitrogen rates and plant residues had little effect upon the concentrations and forms of the elements in the soil solution. Presence of cover crop residues on soil surface decreased the effect of nitrogen fertilizer on Ca leaching. More than 90% of the Ca2+, Mg2+, and K+ were found as free ions. The Al3+ was almost totally complexed as Al(OH3)0. Nitrogen application increased the concentrations of almost all the ions in soil solution, including Al3+, although there was no modification in the leaching gradient.

Soybean root growth and yield in rotation with cover crops under chiseling and no-till

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Organic compounds from plant extracts and their effect on soil phosphorus availability

O objetivo deste trabalho foi avaliar o efeito de compostos orgânicos de extratos de plantas de seis espécies e da fertilização fosfatada na disponibilidade de fósforo no solo. Tubos de 30 cm de altura e 5 cm de diâmetro foram preenchidos com Latossolo Vermelho-Amarelo. Cada tubo constituiu uma parcela, em delineamento completamente casualizado, em arranjo fatorial 7x2, com quatro repetições. Extratos líquidos de aveia-preta (Avena strigosa), nabo forrageiro (Raphanus sativus), milho (Zea mays), milheto (Pennisetum glaucum), soja (Glycine max), sorgo forrageiro (Sorghum bicolor) e água (testemunha) foram aplicados em cada parcela, com ou sem fertilização com fosfato solúvel. Após sete dias de incubação, amostras de solo foram coletadas em várias profundidades, e foram analisadas as formas lábil, moderadamente lábil e não lábil de fósforo no solo. Houve acúmulo de fósforo inorgânico nas frações lábil e moderadamente lábil do solo, como conseqüência da adição dos extratos de plantas, principalmente na camada superficial (0-5 cm). O nabo forrageiro, com maior concentração de ácido málico e maior conteúdo de P no tecido do que outras espécies, foi o mais eficiente em incrementar a disponibilidade de P no solo.

Cover crops and herbicide timing management on soybean yield under no-tillage system

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Phosphorus and potassium balance in soil under crop rotation and fertilization

The use of crop rotation and manure application can provide sustainability for an agricultural production system by improving soil quality and increasing nutrient use efficiency. This study aimed to evaluate the effect of mineral, organic and mineral+organic fertilization on grain yield and on soil phosphorus and potassium balance, in two crop systems under no-till, with and without rotation of cover crops. The experiment was carried out from 2006 to 2008 on a clayey Rhodic Hapludox in Marechal Candido Rondon, Parana State, Brazil. The cropping sequence in the rotation system involving cover crops was black oat + hairy vetch + forage turnip/corn/pigeon pea/wheat/mucuna + brachiaria + sunn hemp, and in the succession system was wheat/corn/wheat/soybean. Organic and mineral+organic fertilizations consisted of the application of solely manure and manure combined with mineral fertilizer, respectively. Soil P and K balances were calculated after the second year of the experiment, up to a depth of 0.40 m. First year corn yields were higher in the crop succession system accompanied by mineral fertilization. In the second year, wheat and soybean yield did not vary between crop systems and nutrient sources, demonstrating the residual effect of crop rotation and manure use. Crop rotation with cover crops resulted in an increase in soil K levels by promoting the recycling of this nutrient in the soil. In both crop systems, the application of mineral and organic fertilizers - either in isolation or in combination - resulted in a negative soil P and K balance in the short term. This represents a threat to the sustainability of the agricultural production system in the long term, due to the depletion of soil nutrient reserves.

Soil erosion fragility assessment using an impact model and geographic information system

A study was taken in a 1566 ha watershed situated in the Capivara River basin, municipality of Botucatu, São Paulo State, Brazil. This environment is fragile and can be subjected to different forms of negative impacts, among them soil erosion by water. The main objective of the research was to develop a methodology for the assessment of soil erosion fragility at the various different watershed positions, using the geographic information system ILWIS version 3.3 for Windows. An impact model was created to generate the soil's erosion fragility plan, based on four indicators of fragility to water erosion: land use and cover, slope, percentage of soil fine sand and accumulated water flow. Thematic plans were generated in a geographic information system (GIS) environment. First, all the variables, except land use and cover, were described by continuous numerical plans in a raster structure. The land use and cover plan was also represented by numerical values associated with the weights attributed to each class, starting from a pairwise comparison matrix and using the analytical hierarchy process. A final field check was done to record evidence of erosive processes in the areas indicated as presenting the highest levels of fragility, i.e., sites with steep slopes, high percentage of soil fine sand, tendency to accumulate surface water flow, and sites of pastureland. The methodology used in the environmental problems diagnosis of the study area can be employed at places with similar relief, soil and climatic conditions.

Cotton development and yield according to nitrogen application and cover crops

Nitrogen application on the cover and the maintenance of straw, conducted by direct seeding, should meet the needs of agriculture and promote soil conservation. This study evaluates the effect of pre-sowing nitrogen application in cotton crops and cover crops by direct seeding, on the development and yield of cotton. It was conducted in the municipality of Selviria-MS during the agricultural years 2005/06, 2006/07 and 2007/08. The experimental design used was a randomized block design consisting of three cover crops (forage turnip, black oat and white oat) and four nitrogen doses (0, 30, 60 and 90 kg of N ha(-1)) in pre-sowing of cotton. In April 2006, April 2007 and April 2008, the assessments of plant development and also harvesting of the experimental plots of cotton cultivars were conducted. The results showed that after planting the cover crops, the yield and development and the heights of cotton plants increased with the use of pre-sowing N of 90 kg ha(-1), also showing that the forage turnip is a coverage plant that provides increased cotton.

Upland rice yield as affected by previous summer crop rotation (soybean or upland rice) and glyphosate management on cover crops

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Nitrogen management in maize cover crop rotations

Winter cover crops can affect N nutrition of the following maize crop. Although legumes have been recommend for maize rotations, in tropical areas grasses may be more interesting because they provide a longer protection of soil surface. Legumes can add N to the system and grasses can compete with maize for the available nutrient. An experiment was conducted in Botucatu, São Paulo State, Brazil, to study N dynamics in the soil surface straw-maize system as affected by N fertilization management and species included in the no-till rotation. Treatments were fallow, black oat (Avena strigosa), pearl millet (Pennisetum glaucum), white lupins (Lupinus albus), black oat fertilized with N. and pearl millet fertilized with N. Maize was grown afterwards in the same plots, receiving 0.0, 60.0 and 120.0 kg ha(-1) of N sidedressed 30 days after plant emergence. Soil, straw and maize samples were taken periodically. The highest corn yields were observed when it was cropped after pearl millet fertilized with N. Nitrogen side dressed application up to 120 kg ha(-1) was not able to avoid corn yield decrease caused by black oat. Grasses can be recommended in maize rotations in tropical areas, provided they receive nitrogen fertilizer and show no allelopathy. Due to its higher ON ratio and dry matter yield they are better than legumes, protecting the soil surface for a longer period. Pearl millet is particularly interesting because it enhances N use efficiency by the following maize crop. For a better N availability/demand synchronism, the cover crops should be desiccated right before maize planting.

Dynamics of aggregate stability influenced by soil management and crop residues

The type of tillage and crop systems used can either degrade or cause a recovery of the structure of agricultural soils. The objective of this study was to determine the structural stability of the soil using mean weight diameter (MWD) of soil aggregates in three different periods of a succession of crops consisting of beans/cover plants/maize under no tillage (NT) and conventional tillage (CT) management systems. Soils were sampled at 0- to 5-cm and 5- to 15-cm depths in three periods (P1, P2, P3): 1) November 2002 (spring/summer), 2) April 2003 (beginning of autumn), and 3) December 2003 (end of spring/beginning of summer). Aggregate stability was determined by wet sieving. The effects of the tillage systems, vegetal residues, and sampling depths on the structural stability of the aggregates were assessed and then related to organic matter (OM) contents. Aggregate stability showed temporal variation as a function of OM contents and sampling period. No tillage led to high MWD values in all study periods. The lowest MWD values and OM contents were observed 4 months after the management of the residues of cover plants. This finding is consistent with the fact that at the time of the samplings, most of the OM had already mineralized. The residues of sunn-hemp, millet, and spontaneous vegetation showed similar effects on soil aggregate stability.

The use of U-isotopes on the study of a weathered cover in Parana basin, Brazil

This paper describes the results of a study involving the sampling of a soil profile developed over sandstone from Itarare Sub-Group at the Parana sedimentary basin, Brazil. It was carried out to integrate chemical and U-isotopes data in order to improve the knowledge of the weathering processes acting in the area. U-238 and its daughter U-234 proved to be important tools for evaluating physical and chemical alteration, allowing to suggest a possible timescale for the development of the more superficial soil horizons.

Estimation of water transit time in soils under Amazon forest cover using variations in sigma18O values.

In an attempt to estimate the soil-water transit time using the variation in 18O values, a statistical model was used. This model is based on linear regression analysis applied to the values observed for soil water and rain water. The time obtained from these correlations represents the mean time necessary for the water to run from one collecting point to the next.-from Authors

Solar energy budgets in central Amazonian ecosystems: a comparison between natural forest and bare soil areas

In order to estimate the deforestation consequences on the actual solar energy budget of the Central Amazon Region, two ecosystems of different characteristics were compared. The present conditions of the region were represented by a typical 'terra firme' forest cover located at INPA's Ducke Forest Reserve, where the measurements necessary to evaluate its solar energy balance were carried out. The second ecosystem, simulating a deforested area, was represented by an area about 1.0 ha without natural vegetation and situated in the same Reserve. In this area lysimeters were placed, two of them filled with yellow latosol and two others with quartzose sand soil. Both soils are representative soils in the region. Their water balances were taken into account as well as the other parameters necessary to compute the solar energy balances. The results showed that water loss by evaporation was about 41.8% of the total precipitation in the yellow latosol lysimeters and about 26.4% for the quartzose sand ones. For the forest cover it was estimated an evapotranspiration of 67.9% of the rainfall amount. In relation to solar energy balance calculated for the forest cover, it was found that 83.1% of the total energy incoming to this ecosystem was used by the evapotranspiration process, while the remaining of 16.9% can be taken as sensible heat. For bare soils, 55.1% and 31.8% of the total energy were used as latent heat by yellow latosol and quartzose sand soils, respectively. So, the remaining amounts of 44.9% and 68.2% were related to sensible heat and available to atmospheric air heating of these ecosystems. Such results suggest that a large deforestation of the Amazon Region would have direct consequences on their water and solar radiation balances, with an expected change on the actual climatic conditions of the region. © 1993.