Abstract Land use systems have a great impact on soil function and microbial diversity in tropical soils. Our study aimed to evaluate soil biochemical indicators and community composition and to assess the relationship between soil biochemical and microbial indicators and bacterial diversity of three agroecosystems (pine forest, soya and sugarcane) and native Cerrado forest in the Brazilian savanna. Soil biochemical indicators (soil organic matter and enzymes) and high-throughput sequencing of 16S rDNA were performed in two topsoil depths (0-5 cm and 5-10 cm). Soil microbial and enzyme activity showed that agricultural soil usage has a negative impact on soil function compared to native and pine forests. Results also revealed higher enzyme activities in 0-5 cm depth compared to 5-10 cm depth, but enzymatic activities depend on land use systems. Soil bacterial community was affected by land use systems and depth, revealing changes in structure and abundance of bacterial composition. Alpha-diversity indexes were higher in the agricultural systems than in the forests, however they showed a significant negative correlation with most of the studied soil microbial and biochemical indicators. Our research had brought new relevant information about the relationship between the soil biochemical indicators and the bacterial diversity in the Brazilian Cerrado.

ABSTRACT The addition of organic residues to agricultural soils has been used as a practical alternative to improve crop quality and health. The objective of this work was to evaluate maize physiological and nutritional responses to the application of compost and biochar combined with urea (N) and N-(n-butyl) thiophosphoric triamide (NBPT). The experiment was performed in plastic pots with 3 kg of soil under greenhouse conditions for 30 days. The compost and biochar were applied at the rate of 0.3 ton ha-1, using an amount of nutrient (nitrogen, phosphorus and potassium) demanded by crop growth. The physiological responses of maize were monitored by measuring the plant height, stalk diameter, leaf chlorophyll content, shoot dry weight and root dry weight. The nutritional responses of maize were assessed by using the nutrient concentration and the total nutrient assimilation by the plants. The results showed that the addition of compost or biochar did not alter the maize physiological response compared to the addition of mineral fertilizer used under the same conditions. However, a difference occurred in the maize nutritional responses to the compost and biochar amendments combined with urea and NBPT. The greatest N concentration in maize was observed in the treatment consisting of biochar combined with urea + NBPT. All the treatments in which compost or biochar was applied in combination with urea and NBPT presented greater total N assimilation compared to the treatment with conventional fertilization. The results of this survey showed that the combination of urea and NBPT improved the nitrogen-use efficiency of maize.

A atividade e cinética das fosfatases do solo são importantes indicadores para avaliar a qualidade do solo em sítios específicos tais como Cerrado (Savana brasileira). Este estudo objetivou determinar a atividade e os parâmetros cinéticos da fosfatase do solo em sistemas do Cerrado. A atividade de fosfatase do solo foi avaliada em amostras de Cerrado nativo (CN), plantio direto (PD), plantio convencional (PC) e pastagem com Brachiaria brizantha (PBb) e avaliada com tampão de acetato (TA), tampão tris-HCl (TT), tampão modificado universal (TMU) e baixo-TMU. A equação de Michaelis-Menten e o modelo de Eadie-Hofstee foram usados para avaliar os parâmetros cinéticos da fosfatase do solo usando diferentes concentrações de p-nitrofenol fosfato (p-NFF). O TMU indicou a menor atividade de fosfatase do solo, enquanto que TA em CN e PC, a maior atividade. O baixo-TMU diminuiu as interferências na avaliação da atividade de fosfatase do solo quando comparado à TMU, sugerindo que ácidos orgânicos interferem na atividade da fosfatase do solo. Em CN e PD, a atividade de fosfatase do solo com TT foi similar à TA e baixo-TMU. Os valores de Km da equação de Michaelis-Menten foram maiores em CN do que em PD, indicando menor afinidade da atividade de fosfatase para o substrato em CN. Os valores de Vmax foram também maiores em CN quando comparados com PD. O modelo de Eadie-Hofstee indicou que CN tem mais isoformas de fosfatase no solo quando comparado com PD. O estudo mostrou que o tipo de tampão é de fundamental importância para avaliar a atividade de fosfatase em solos de Cerrado.

The activity and kinetics of soil phosphatases are important indicators to evaluate soil quality in specific sites such as the Cerrado (Brazilian Savanna). This study aimed to determine the activity and kinetic parameters of soil phosphatase in Cerrado systems. Soil phosphatase activity was assessed in samples of native Cerrado (NC), no-tillage (NT), conventional tillage (CT) and pasture with Brachiaria brizantha (PBb) and evaluated with acetate buffer (AB), tris-HCl buffer (TB), modified universal buffer (MUB) and low MUB. The Michaelis-Menten equation and Eadie-Hofstee model were applied to obtain the kinetic parameters of soil phosphatase using different concentrations of p-nitrophenol phosphate (p-NPP). MUB showed the lowest soil phosphatase activity in all soils whereas AB in NC and NT presented the highest. Low MUB decreased interferences in the assessment of soil phosphatase activity when compared to MUB, suggesting that organic acids interfere on the soil phosphatase activity. In NC and NT, soil phosphatase activity performed with TB was similar to AB and low MUB. Km values from the Michaels-Menten equation were higher in NC than in NT, which indicate a lower affinity of phosphatase activity for the substrate in NC. Vmax values were also higher in NC than in NT. The Eadie-Hofstee model suggests that NC had more phosphatase isoforms than NT. The study showed that buffer type is of fundamental importance when assessing soil phosphatase activity in Cerrado soils.

Os sistemas convencional (SC) e plantio direto (SPD) alteram a disponibilidade de nutrientes no solo e, consequentemente, modificam a resposta da microbiota do solo à adição de nutrientes tais como carbono (C) e fósforo (P). O objetivo deste estudo foi avaliar a resposta da microbiota do solo à adição de C (glicose) e P (Na2HPO4.7H2O) sob os SC e SPD no Cerrado brasileiro. Em resposta à adição de glicose, o sistema SPD apresentou maior taxa de respiração microbiana e consumo de glicose do que o SC. A melhor resposta da microbiota à adição de carbono foi após 12 horas de incubação no SPD e 24 horas no SC. A adição de P produziu um maior efeito sob SC do que SPD. Após a incubação, os indicadores bioquímicos, como respiração microbiana, consumo de glicose, atividade de desidrogenase e rendimento metabólico, confirmaram a maior demanda de glicose em SPD e de P em SC. Esses resultados demonstraram que as adições de C e P alteram significativamente a resposta microbiana do solo, sugerindo que os microorganismos do solo apresentam uma demanda diferencial de nutrientes entre os sistemas SC e SPD.

Conventional tillage (CT) and no-tillage (NT) management systems alter soil nutrient availability and consequently modify soil microbial response to nutrient additions such as carbon (C) and phosphorus (P). The objective of this study is to evaluate microbial response to the addition of C (glucose) and P (Na2HPO4.7H2O) under CT and NT in the brazilian Cerrado. In response to glucose addition, the NT system yielded higher microbial respiration rates and glucose consumption than the CT system. The best microbial response to C addition was after 0 - 12 h incubation in NT and 0 - 24 h in CT. The addition of P produced higher demand under CT than NT. After incubation, biochemical indicators such as microbial respiration, glucose consumption, dehydrogenase activity and metabolic yield confirmed the higher glucose demands under NT and higher phosphorus demands under CT. These results demonstrate that C and P addition alter significantly the microbial response, suggesting that soil microorganisms present nutrient differential demands between CT and NT management systems.