Gedi Jorge Sfredo

Doses e métodos de aplicação de nitrogênio em girassol

A sunflower field experiment was carried out during the growing seasons of 1991/92; 92/93 and 93/94, on an Typic Eutrorthox. The applied levels of nitrogen (N) were 0, 30, 60 and 90 kg ha-1 and the application methods were: 1. incorporated/moldboard plow (broadcasted with incorporation with moldboard plow down to 30 cm depth before sowing); 2. incorporated/disk bars (broadcasted with incorporation with disk bars before seedbed preparation); 3. incorporated/grade/split (30% of N broadcasted with incorporation with disk bars before seedbed preparation and the remaining N 30 days after the sunflower emergency). The effect of different levels and methods of N supply were evaluated through grain yield, weight of 1,000 achenes, plant height, and stem diameter. Phosphorus and potassium were applied together with N fertilization. The experimental design was a randomized blocks with split-plots and four replicates, with N rates in the main plots and methods in the split-plots. A density of 42,857 plants ha-1 occupied a total area of 3,528 m2. Grain yield increased with N levels up to 90 kg ha-1, while the economic level was obtained with 17.5 kg ha-1 of N. The highest grain yield and 1,000 achenes weight were achieved during the 1993/94 season, while the highest plant height and stem diameter were obtained in 1991/92. Different methods of N application did not affect grain yield. On the other hand, the greatest 1.000 achenes weight was obtained with the incorporated/grade/split method of N incorporation. However, for the other variables N incorporation with moldboard plow gave greater values.

Lime and Cattle Manure in Soil Fertility and Soybean Grain Yield Cultivated in Tropical Soil

Most tropical soils have high acidity and low natural fertility. The appropriate application of lime and cattle manure corrects acidity, improves physical and biological properties, increases soil fertility, and reduces the use of chemical and/or synthetic fertilizers by crops, such as soybean, the main agricultural export product of Brazil. This study aimed to assess the effects of the combination of the application of dolomite limestone (0, 5, and 10 Mg ha−1) and cattle manure (0, 40, and 80 Mg ha−1) on grain yield and the chemical properties of an Oxisol (Red Latosol) cultivated with soybean for two consecutive years. The maximum grain yield was obtained with the application of 10 Mg ha−1 of lime and 80 Mg ha−1 of cattle manure. Liming significantly increased pH index, the concentrations of calcium (Ca2+) and exchangeable magnesium (Mg2+), and cation exchange capacity (CEC) of soil and reduced potential acidity (H+ + Al3+), while the application of cattle manure increased pH level; the concentrations of potassium (K+), Ca2+, and exchangeable Mg2+; and CEC of the soil. During the 2 years of assessment, the greatest grain yields were obtained with saturation of K+, Ca2+, and Mg2+ in CEC at the 4.4, 40.4, and 17.5 levels, respectively. The results indicated that the ratios of soil exchangeable Ca/Mg, Ca/K, K/Mg, and K/(Ca+Mg) can be modified to increase the yield of soybean grains.

Efficiency of Sulfur Application on Soybean in Two Types of Oxisols in Southern Brazil

Modern agricultural techniques have been increasing the yield of soybean (Glycine max (L.) Merr.) while also causing increasing removal of sulfur (S) from the soil. Besides this, the use of concentrated fertilizers with this element and inadequate soil management, with consequent formation of organic matter with low S concentrations, has been causing frequent symptoms of deficiency in the plants. To assess the effect of S on soybean yield and to establish critical levels of sulfur sulfate (S-SO42-) available in the soil, two experiments were conducted over a 2-year period in the Paraná State, Brazil, in fields containing Typic Haplorthox and Typic Eutrorthox soils, located in the Ponta Grossa and Londrina Counties, respectively. The experimental design was randomized blocks with five S rates (0, 25, 50, 75, and 100 kg ha−1) and four replicates. The source used was elementary S with 98 percent purity. The maximum estimated yields on average for the 2 years were obtained with application of 49.9 and 63.0 kg ha−1 in the Typic Haplorthox and Typic Eutrorthox soils, for an overall average of 56.4 kg ha−1, with concentrations of available S-SO42- in the 0- to 20-cm depth of 16.9, 19.3m and 17.1 mg kg−1, respectively, values greater than the 10 mg kg−1 indicated as the adequate concentration for soybean plant. In turn, at the 21- to 40-cm depth, the S concentrations were 49.5, 74.2, and 56.4 kg ha−1. The efficiency of the fertilization diminished with increasing S rates, in both soil types, while the greatest yield efficiency was obtained in the plants grown in the Typic Haplorthox soil.

Agronomic Efficiency of Two Types of Lime and Phosphate Fertilizer Sources in Brazilian Cerrado Soils Cultivated with Soybean

With the increase in phosphate fertilizer prices, there is a need to find lower-cost alternatives that are as efficient as soluble sources such as single (SSP) and triple superphosphate (TSP). In Brazil’s northern and northeastern regions, there are reserves of igneous rocks with low solubility containing high concentrations of total phosphorus (P) that can be used to produce fertilizers, such as thermalphosphates. To assess the efficiency of sources of P and two types of lime on soybean yield, a field experiment was carried out in an area with dystrophic Red Latosol (Oxisol) in a Cerrado region in the southern part of Maranhão State. The experimental design was randomized blocks in a 2 × 3 × 4 factorial scheme, with four replicates. The treatments were two types of lime [calcitic (CL) (<5 dag kg−1 of MgO) and dolomitic (DL) (>13 dag kg−1 of MgO)], three phosphate fertilizer sources [triple superphosphate (TSP), “Yoorin” thermalphosphate (YT), and experimental thermalphosphate (ET)], and four rates of phosphorus pentoxide (P2O5; 0, 100, 200, and 300 kg ha−1). After 2 years of cultivation, the application of DL resulted in greater soybean yields than the application of CL. The two lime types influenced the pH, carbon (C), calcium (Ca), and magnesium (Mg) concentrations as well as the Ca/Mg, Ca/K, and Mg/K ratios in the soil. With respect to sources of P, the YT applied in the soil with DL produced an agronomic efficiency index (AEI) similar to that of TSP, whereas in the soil with CL, the TSP, YT, and ET were similar, with maximum technical efficiency (MTE) under both conditions starting at 230 kg ha−1 of P2O5. The critical concentration of available phosphorus (P) in the soil (Mehlich-1 extractant) for cultivation of soybean under the climate and soil conditions studied was between 5.0 and 6.0 mg kg−1.