V Victor Hugo Alvarez

Brazilian soil science: from its inception to the future, and beyond

The present essay is meant to provide some background on the evolution of the soil science community in Brazil, since its inception, to describe its current situation, and to outline a number of opportunities and challenges facing the discipline in decades to come. The origin of Brazilian agronomy dates back to the beginning of the 19th century as a subdiscipline of botany, and its association with chemistry would later establish it as a science. In the middle of the 19th century, agricultural chemistry was born as a result of this association, leading to the establishment of edaphology, a branch of Soil Science. Another branch of Soil Science, known as pedology, was established as an applied and scientific knowledge in Brazil during the middle of the 20th century. During the same period, the Brazilian Soil Science Society (SBCS) was created, merging the knowledge of both branches and gathering all scientists involved. Twenty years after the SBCS foundation, the creation of Graduate Programs made Brazilian Soil Science enter the modern era, generating crucial knowledge to reach the current levels of agricultural productivity. Part of a community composed of 25 Soil Departments, 15 Graduate Programs and a great number of institutions that promote research and technology transfer, Brazilian soil scientists are responsible for developing solutions for sustainable development, by generating, adapting and transferring technology to the benefit of the country. The knowledge produced by SBCS members has been particularly significant for Brazil to achieve the status of most competitive tropical agriculture in the world. In the future decades, Soil Science will still remain topical in discussions regarding environment care and production of food and fibers, in addition, it will be essential and strategic for certain issues, such as water quality, reducing poverty and development of renewable sources of energy.

Sensitivity of Soil P Availability Tests to Ca-P in Oxisols

ABSTRACT We assessed the sensitivity of mixed exchange resin (MER) and Mehlich-3 (M3) to calcium-bound phosphate (Ca-P) in Oxisols. These methods were compared with Mehlich-1 (M1) and anion exchange resin (AER), which have high and low sensitivity, respectively, to this soil P form. We used maize (Zea mays L.) as a test plant. Three samples from two Oxisols were treated with five ratios of Triple Superphosphate—TS and Bayóvar Phosphate Rock—BPR (0 + 100; 25 + 75, 50 + 50, 75 + 25 and 100 + 0% TS + BPR). The MER extracted more P than AER and M3 at the highest BPR:TS ratios (high Ca-P) and similar quantities at the higher TS:BPR ratios (low Ca-P) for two soil samples. Unlike M1-extracted P, M3-P, AER-P, and MER-P positively correlated with maize dry matter production and P uptake. Mehlich-3 and MER were suitable to assess P availability in high Ca-P Oxisols.

Quantification of permanent and variable charges in reference soils of the State of Pernambuco, Brazil

The electrical charges in soil particles are divided into structural or permanent charges and variable charges. Permanent charges develop on the soil particle surface by isomorphic substitution. Variable charges arise from dissociation and association of protons (H+), protonation or deprotonation, and specific adsorption of cations and anions. The aim of this study was to quantify the permanent charges and variable charges of Reference Soils of the State of Pernambuco, Brazil. To do so, 24 subsurface profiles from different regions (nine in the Zona da Mata, eight in the Agreste, and seven in the Sertao) were sampled, representing approximately 80 % of the total area of the state. Measurements were performed using cesium chloride solution. Determination was made of the permanent charges and the charges in regard to the hydroxyl functional groups through selective ion exchange of Cs+ by Li+ and Cs+ by NH4+, respectively. All the soils analyzed exhibited variable cation exchange capacity, with proportions from 0.16 to 0.60 and an average of 0.40 when related to total cation exchange capacity.

Uniformity distribution index of ammonium, nitrate, potassium and phosphorus in fertigated Oxisols

Fertigation if conducted inadequately may cause soil salinization and consequently leaching of nutrients can pollute ground water. An index is proposed to determine the uniformity of distribution of ammonium, nitrate, potassium and phosphorus in columns of fertigated Oxisols, which relates the highest content of the nutrient in a column segment with the mean nutrient content in the experimental unit. The higher the index value, the more irregular is the nutrient distribution. This index was calculated based on laboratory data evaluated in a 4 x (1 + 6) factorial design including four Oxisols of Minas Gerais (two distrophic Red-Yellow, one dystroferric Red and one dystrophic Red oxisol), one control (application of deionized water) and six application modes of application of 1 mmolc of N-NH4+, 1 mmolc N-NO3-, 2 mmolc K and 2 mmolc dm-3 P. The coefficient of variation was calculated for the content of each nutrient along the columns. The ratio between the mean and the highest nutrient content was computed as well, considering the soil and the treatment. It was inferred that the ratio mean/highest content is an adequate index of uniformity of nutrient distribution to evaluate the movement of major mobile ions such as nitrate, ammonium and potassium in the soil. The coefficient of variation is less appropriate to show the uniformity of nutrient distribution.Fertigation if conducted inadequately may cause soil salinization and consequently leaching of nutrients can pollute ground water. An index is proposed to determine the uniformity of distribution of ammonium, nitrate, potassium and phosphorus in columns of fertigated Oxisols, which relates the highest content of the nutrient in a column segment with the mean nutrient content in the experimental unit. The higher the index value, the more irregular is the nutrient distribution. This index was calculated based on laboratory data evaluated in a 4 x (1 + 6) factorial design including four Oxisols of Minas Gerais (two distrophic Red-Yellow, one dystroferric Red and one dystrophic Red oxisol), one control (application of deionized water) and six application modes of application of 1 mmolc of N-NH4, 1 mmolc N-NO3, 2 mmolc K and 2 mmolc dm-3 P. The coefficient of variation was calculated for the content of each nutrient along the columns. The ratio between the mean and the highest nutrient content was computed as well, considering the soil and the treatment. It was inferred that the ratio mean/highest content is an adequate index of uniformity of nutrient distribution to evaluate the movement of major mobile ions such as nitrate, ammonium and potassium in the soil. The coefficient of variation is less appropriate to show the uniformity of nutrient distribution.

Effects of nitrate, phosphate and sulfate combinations on growth and kinetics of phosphate and sulfate uptake by eucalypt seedlings

This trial was carried out to study the effect of nitrate, phosphate and sulfate on growth and kinetics of P and S uptake by Eucalyptus grandis seedlings. The seedlings had their taproot pruned and were placed in sets of geminated plastic pots, with the root system split and growing in solutions containing the three nutrients, or with one of them isolated in one of the geminated pots. Seedling shoot dry weight when the solution in both pots contained the three nutrients was higher than that in the other treatments, which did not differ. Absence of NO3 − in the nutrient solution significantly reduced root dry weight. When both pots contained the three nutrients, the Km-SO4 2− was two to three times lower than that of the other four treatments. Influx of SO4 2− and H2PO4 − increased when NO3 − was supplied separately from SO4 2− or H2PO4 −.