Volume 32, Number 5, 2008

The nutrient use efficiency, expressed by the ratio between the produced biomass and nutrient content, is an important adaptive characteristic of plants, particularly of those cultivated in low-fertility soils. A high P-use efficiency (PUE) is conferred by high P remobilization rates, i.e., P transport to regions of greater metabolic demand in the plant. High P remobilization rates have been associated with high acid phosphatase (APase) and ribonuclease (RNase) enzyme activities. In our study, we evaluated the activity of these enzymes […]

More and more studies, including in Brazil, have suggested the use of microbial biomass carbon (MBC) as a bioindicator of soil quality. Most studies employ two methods: the pioneer of fumigation-incubation (FI), in which the MBC is estimated based on CO2 emission from fumigated and non-fumigated soil samples after 10 days of incubation and fumigation-extraction (FE), in which MBC is estimated based on C extraction from fumigated and non-fumigated soil samples after 12 h. However, in Brazil the correlation between both […]

Although new studies describe the use of PGPR (Plant Growth-Promoting Rhizobacteria) in Brazil, they rarely evaluate the natural existence of these bacterial species in the soil. The objective of this study was to evaluate PGPR in two samples under different use types, one with native forest and the other with eucalyptus, through construction and sequencing of a metagenomic DNA library. Using specific probes from the internally transcribed region of 16S-23S rRNA genes, fragments of PCR products were inserted into the vector […]

Soil test is the most widely used tool to determine the soil fertility status and fertilizer demand for crop production. Tables of soil analysis interpretations and fertilizer recommendation based on field experiments are required for this purpose. A recommendation system normally aims at supplying crop requirements and improving soil fertility levels to a sufficient degree. To obtain information for building K interpretation and recommendation tables, seven experiments were carried out with wheat, corn and soybean in four Paraguayan Departments: two […]

Nitrogen is a plant nutrient of great importance. To determine optimum N levels for wheat, a field trial was carried out in a Red Latosol, during the winter of 2005, at Embrapa Cerrados, Planaltina (DF – Brazil). The experiment was set up in a randomized block design, with six replications and the treatments consisted of six N doses (0, 70, 140, 210, 280 and 350 kg ha-1). Soil samples were collected in the 0-20 cm and 20-40 cm layers and three different chemical extractors […]

Phosphorus (P) is one of the most critical elements for agriculture, not only by the high P requirement for adequate crop growth and development, but also by the gradual scarcity of its natural sources. The differentiation among genotypes is required for further mechanism investigation, and to combine different mechanisms at the same individual which might allow superior tolerance. This work aimed to differentiate, in hydroponic solution, wheat genotypes with contrasting P deficiency tolerance. Three studies were carried out. In the […]

Cattle slurry solid fraction (FSC1 and FSC2, collected from open and closed sinkholes, respectively) was collected from two dairy farms and composted with and without straw, in static and in turned piles. Thermophilic temperatures were attained soon after separation of FSC1, which was collected at lower rate, and increased to a daily maximum temperature of 68 °C in the static pile with straw. However, the temperature in the FSC2 piles did not reach temperatures above 51 °C. Straw addition to slurry solid […]

Knowledge about the nutritional demand of a crop is essential for fertilizer recommendation. In this study nutrient concentration and accumulation in leaves and fruits of Jatropha curcas L. were measured and nutrient extraction by fruits harvested between the 1st and 4th year of cultivation were estimated. The study was carried out at the Paraiso Farm, iin Viçosa, Minas Gerais State. Four leaf and fruit samples, each one containing 15 leaves or 20 fruits were randomly collected from an area with […]

Shoot biomass is considered a relevant component for crop yield, but relationships between biological productivity and grain yield in legume crops are usually difficult to establish. Two field experiments were carried out to investigate the relationships between grain yield, biomass production and N and P accumulation at reproductive stages of common bean (Phaseolus vulgaris) cultivars. Nine and 18 cultivars were grown on 16 m2 plots in 1998 and 1999, respectively, with four replications. Crop biomass was sampled at four growth […]

Understanding the soil organic P (Po) cycle is important to improve the P fertilization management in low-input tropical agricultural systems. The aim of this study was to evaluate Po content and labile P fractions, and microbial biomass P in soils under different cocoa agroecosystems. Mean total Po was 193 mg kg-1 and accounted for 7.8 to 36.3 % of the total extracted P. Mean labile Po was 15 mg kg-1 and accounted for 33.1 to 81.9 % of the total labile P. In cocoa agrosystems, the […]