Biocarvão de bambu e fontes de fósforo afetando a disponibilidade de p e o crescimento de feijão caupi e milho em latossolo amarelo distrófico da Amazônia

Abstract

The use of biochar has been motivated by research carried out with black carbon from Amazonian Dark Earths, showing that black carbon (biochar) is important in the stability of organic matter and for improving the physical, chemical and biological properties of the soil. The large amounts of iron oxide, aluminum and clay minerals with low activity are the main factors responsible for the high fixation of phosphorus in tropical soils. The objective of this study was to evaluate the effect of biochar from bamboo, produced under different carbonization temperatures (400°, 500° and 600° C), on the availability of phosphorus from different common sources (natural phosphate of ARAD (NP), simple superphosphate (SSP) and triple superphosphate (TSP)) in a Yellow Oxisol of Central Amazonia. An experiment was conducted in a greenhouse with two alternating crops of cowpea (Vigna unguiculata) and maize (Zea mays) in a completely randomized design in a 3x3 factorial, with three carbonization temperatures of biochar and three phosphorus sources: the sources of phosphate were applied to be equivalent to 100 kg of P2O5 per ha-1. The biochar was applied to be equivalent to 40 t ha-1. Complementary fertilization was carried out at the beginning of each crop in the following doses: 45 kg N ha-1 (urea), 72 kg K2O ha-1 (potassium chloride). The beans were harvested at the beginning of flowering and the maize 45 days after germination. The following variables were measured: availability of soil nutrients, nutrient accumulation and total shoot dry matter in each crop. The results showed that the first crop of cowpea had the highest increment of total shoot dry matter (TSDM) obtained in the treatment 500oC biochar with ARAD (BIO500NP) (6.9 g), an increase of approximately 360% over the control (1.9 g), followed by BIO400FN (6.8 g) with an increase of 300%. In the treatments with biochar at 400° C, the concentrations of soil P increased according to the source (NP 12.60 > SSP 11.20 > TSP 10.80 mg dm-3), but the opposite occurred with the treatments receiving biochar at 500° C (NP 10.40 < SSP 11.60 < TSP 14.20 mg dm-3) and in treatments with biochar 600° C soil P was uniform. For all the treatments that received biochar at 500° C the values of exchangeable K in the soil ranged between 5.2 and 8.5 mg dm-3, considered high. The treatments with SSP showed high levels of sulfur in the soil, higher than 31.0 mg dm-3, regardless of the carbonization temperature. In the second crop of cowpea the TSDM of BIO600TSP (5.9 g) was similar to the BIO400NP (5.7 g) and 19% greater than the control (5.1 g). The phosphorus content in soils with BIO400FN (14.8 mg dm-3) and BIO500SFT (15.0 mg dm-3) were very similar. Although the TSDM of two maize crops showed no effect of treatments, the largest increases occurred with NP, regardless of the carbonization temperature; the same results were observed for the levels of available P in soil that showed high levels and were similar to the other more soluble phosphate sources. In treatments with biochar at 500 ° C the values of exchangeable K were higher, ranging from 5.20 to 8.50 mg dm-3. The different phosphate sources showed similar responses on P availability and also on bean grown in the presence of biochar. The higher amounts of K was observed in the treatments that received the biochar at 500º C.