Long-term effect of biochar-based fertilizers application in tropical soil: Agronomic efficiency and phosphorus availability.

Incorporation of phosphorus (P) into an organic matrix may be an effective strategy to increase plant P use efficiency in high P-fixing soils. The objective of this work was to evaluate the effect of biochar-based fertilizers (BBFs), produced from poultry litter (PLB) and coffee husk (CHB) enriched with phosphoric acid and magnesium oxide, in combination with triple superphosphate (TSP) on plant growth and soil P transformations. Treatments were prepared as: TSP, CHB, PLB, CHB + TSP [1:1], CHB + TSP [3:1], PLB + TSP [1:1] and PLB + TSP [3:1]; with numbers in brackets representing the proportion of BBF and TSP on a weight basis. Cultivations were: Mombasa grass, maize, and common bean interspersed with fallow periods. After cultivations, a sequential extraction procedure was employed to determine P distribution among different P pools. A kinetic study was performed and revealed that TSP released approximately 90% of total P, and BBFs less than 10% in the first hour. BBF alone or in combination with TSP presented higher or similar biomass yields, relative agronomic effectiveness, and P uptake when compared with TSP. As for the soil, BBFs increased non-labile P fractions, which can be due to pyrophosphate formed during pyrolysis. According to these results, BBFs could totally or partially replace conventional soluble P fertilizers without compromising crop yield either in the short and long-term.

Aging of biochar-based fertilizers in soil: Effects on phosphorus pools and availability to Urochloa brizantha grass.

Water-soluble phosphate fertilizers release phosphorus (P) to soils promptly, causing P fixation and low plant availability in highly weathered tropical soils. Therefore, the development of strategies to improve P use efficiency is needed. We hypothesized that biochar-based fertilizers (BBFs) can provide available P to plants and improve P use efficiency when compared with soluble fertilizers. Thus, triple superphosphate (TSP) and phosphoric acid (H3PO4) were pyrolyzed with and without magnesium oxide (MgO) and poultry litter to produce slow-release P BBFs. A pot experiment under greenhouse conditions was performed to evaluate agronomic efficiency of BBFs compared with TSP in an Oxisol. The treatments were incubated over 100 days after the application of 25, 50, 100, and 200 mg kg-1 of P. Three controls were used, including 200 mg kg-1 of P as TSP incubated for 100 days (named TSPincubation) and applied immediately before sowing (named TSPplanting) and a negative control (without P). Marandu grass (Urochloa brizantha cv. Marandu) was cultivated in pots for three cycles of 40 days each. After cultivation, a sequential extraction procedure was used to determine the P distribution among different P pools. The shoot dry matter yield in the first cropping cycle was higher at the highest P rate for TSPplanting. PLB-H3PO4-MgO showed 9% increase in the shoot dry matter when compared with TSPincubation in the first cropping cycle. In subsequent cropping cycles, all BBFs promoted higher biomass yield when compared with TSPplanting. There was an increase in the labile and moderately labile P fractions in soil after cultivation with PLB-TSP. The results suggest that BBFs can enhance P use efficiency in tropical soils in the middle- to long-term run due to slow-release profile that prevent P fixation and promote higher residual effect of fertilization.

Atributos químicos do solo adubado com lodo de esgoto estabilizado por diferentes processos e cultivado com girassol / Soil chemical attributes fertilized with sewage sludge stabilized by different processes and cultivated with sunflower

Objetivou-se com este trabalho avaliar os atributos do solo em resposta a adubação com lodo de esgoto submetido a diferentes processos de estabilização. O experimento foi desenvolvido em solo CAMBISSOLO HÁPLICO, com os tratamentos: testemunha (sem adubação), adubação com lodo de esgoto solarizado, adubação com lodo de esgoto compostado, adubação com lodo de esgoto vermicompostado, adubação com lodo de esgoto caleado e adubação química recomendada para a cultura. Utilizou-se o delineamento experimental em blocos casualizados, com 4 repetições. O lodo de esgoto estabilizado de diferentes formas não influenciou os teores de matéria orgânica, o pH, a soma de bases (SB), a saturação por bases (V), a CTC efetiva (CTC(t)), a CTC potencial (CTC(T)) e os teores de H+Al do solo quando comparado à adubação química e ao tratamento sem adubação, exceto o lodo de esgoto caleado, que aumentou o pH, a SB, a V e a CTC(t) do solo.

The objective of this study was to evaluate the soil properties in response to fertilization with sewage sludge under different stabilization processes. The experiment was conducted in Haplic Cambisol, with the treatments: control (without fertilization), fertilization with sewage sludge solarized, fertilization with compost sewage sludge, fertilization with sewage sludge vermicomposted, fertilization with limed sewage sludge and chemical fertilizer recommended for culture. It was used a randomized block design with four replicates. The sewage sludge did not affect the organic matter content, pH, SB, V%, CTC(t), CTC(T) and the contents of H + Al when compared to chemical fertilizer and treatment without fertilization, except the limed sewage sludge, which increased the pH, SB, CTC(t), and V% of the soil.