L. C. Hernani

Perdas por erosão e rendimentos de soja e de trigo em diferentes sistemas de preparo de um latossolo roxo de Dourados (MS)

Soil and water losses were evaluated from 1987 to 1995, on a very clayey red dusky latosol, with 0.03 m m-1 slope, of Embrapa-Centro de Pesquisa Agropecuaria do Oeste, at Dourados, Mato Grosso do Sul State, Brazil. Soil tillage systems used for growing wheat and soybean in succession were: chisel plow + tandem disk (ES), offset disk + tandem disk (GP), no tillage (PD) and conventional tillage, with no vegetable cover (DE). All tillage operations and seeding were in the up and down hill. PD was the most efficient tillage system to control soil and water losses and was the most productive. GP was the least efficient. Means of soil and water losses for PD, ES, GP and DE were, respectively: 0.8; 2.8; 5.3 and 7.3 t ha-1 year-1, and 27, 80, 112, and 149 mm year-1. Compared to DE, the PD controlled 89% of soil and 82% of water erosion losses, and yielded 17% more soybean and wheat grain than GP. As for wheat, ES was 12% more productive than GP. Rainfall-runoff erosivity factor (R) was 6.411 MJ mm ha-1 h-1 year-1, and the erodibility fator (K) was 0.0045 t h MJ-1 mm-1, reflecting characteristics of high infiltration and high internal drainage of this soil. During the 1994/95 growing season, the highest soil loss period per time unit was from seedbed preparation to seeding soybean, and the period of highest absolute soil erosion losses was from 30 to 60 days after seeding soybean. This shows the great importance of soil cover, specially during the inicial cropping phase, and support the recommendation of the no tillage system for this region.

Eficiência de extratores de fósforo em dois latossolos do Mato Grosso do Sul

With the objective of evaluating the efficiency of three phosphorus extractors in two Mato Grosso do Sul State oxisols, in Brazil, one greenhouse experiment was carried out with three P sources (triple superphosphate, Araxa rock phosphate and Gafsa rock phosphate), all in five levels (0, 50, 150, 450, and 600 mg per kg of soil). Common bean was used as test plant. In order to evaluate the phosphorus availability in the soils, the dry matter yield, the above ground phosphorus content, the plants height and the number of trifoliate leaves were correlated with the extracted phosphorus by Mehlich-1, Mehlich-3 and ion exchange resin methods. Mehlich-3 and resin were more sensitive to soil variations. According to their efficiencies, the extractors were classified in the following order: resin > Mehlich-3 > Mehlich-1. The resin method showed the best correlations with the plants characteristics, thus showing to be the most suitable in forecasting the available P in different soils and P sources. The best correlations were yielded by the resin and Mehlich-3 methods.

Eficiência relativa de frações granulométricas de calcários Sul-Mato-Grossenses

In Mato Grosso do Sul, Brazil, there are limestone mines formed from sedimentary rocks, which have higher initial reactivity than that of metamorphic rock limestones. At Embrapa-Centro de Pesquisa Agropecuaria do Oeste (CPAO), Dourados, Mato Grosso do Sul State, Brazil, the relative efficiency of limestone granularity fractions were evaluated under greenhouse conditions, using Dark-Red Latosol and Dusky-Red Latosol soils, both Oxisols. Each soil was amended with a dosage of lime high enough to elevate the pH (CaCl2) to 6.0. The treatments, at a completely randomized experimental design, were a control (without lime) and four granularity fractions: 4.00 to 2.00 mm; 2.00 to 0.84 mm; 0.84 to 0.30 mm; and 0.30 to 0.21 mm. Three limes were tested: calcitic of sedimentary origin (CS) and calcitic (CM) and dolomitic (DM) of metamorphic origin. No differences were observed on the effectiveness of the limes of the same origin in increasing the soil pH level. The relative efficiency of the different limes was influenced by the geologic origin, the granularity, the soil type, and the incubation period. The initial CS relative efficiency was higher than the ones from metamorphic origin, and was higher or at least equal up to three months of incubation.

UNIFORMIDADE DE DISTRIBUIÇÃO DE ÁGUA EM SISTEMA DE IRRIGAÇÃO POR ASPERSÃO DO TIPO CONVENCIONAL

The knowledge about the distribution uniformity is very importam when working with sprinkler irrigation because it allows the identification of under-and-over-irrigated areas. In an experiment carried out at Centro de Pesquisa Agropecuaria do Oeste (EMBRAPA-CPAO), Dourados, Mato Grosso do Sul State, the distribution uniformity of a conventional type sprinkler irrigation system was ascertained. One sprinkler, mounted at height 70cm and operating under four working pressures (280, 340, 400 and 480 kPa) was used. Using simulation of overlapping, the distribution of precipitation for four spacings (12x12, 12x18, 18x18 and 18x24m) was obtained. The experimental area was divided into 9m2 plots. At the center of each plot one pluviometer was installed at height 30cm. The wind speed was measured with an anemometer mounted 2m above ground. Two 60 minutes assays were carried out for each working pressure. The distribution uniformity was calculated by the following coefficients: the Uniformity Coefficient of Christiansen, the Coefficient of Wilcox and Swailes, the Uniformity Coefficient of Benami, the Criddle Pattern Efficiency and the Beale Pattern Efficiency. The highest coefficients were the ones with 12x18 and 12x12 spacing. In general, the uniformity decreased with increasing wind speed, with similar wind speed there was increase in uniformity with increasing work pressure. The highest uniformity indices were obtained with Coefficient of Christiansen, followed by Coefficient of Wilcox and Swailes, while Coefficient of Benami provided the lowest values.