Djalma Martinhão Gomes de Sousa

Qualidade de solo submetido a sistemas de cultivo com preparo convencional e plantio direto

The objective of this study was to evaluate the quality of an Oxisol under tillage and no-tillage systems. Two experimental areas were studied, both located in Embrapa Cerrados, Planaltina, DF, Brazil, with eight and ten years of cropping. Soil samples were collected from different depth layers in the experimental plots and native cerrado vegetation area. The following soil atributes were evaluated: bulk density, soil porosity, available water capacity, degree of flocculation, soil resistance to penetration, organic matter content, cation exchange capacity, equilibrium phosphorus, microbial biomass carbon and basal respiration. The data obtained were compared with referential values related to soil quality. The soil quality under both systems is similar, considering the soil physical attributes. The values for organic matter and equilibrium phosphorus are also similar, but the cation exchange capacity is higher for soil under no-tillage. Concerning the biological attributes, the soil under no-tillage presents higher biological activity. The soil quality is similar, under both cropping systems.

Sistemas de manejo e os estoques de carbono e nitrogênio em latossolo de cerrado com a sucessão soja-milho

Os estoques de C e N no solo sao determinados pelo balanco entre adicao e perda no sistema, sendo o preparo do solo e o sistema de culturas determinantes nesse processo. Este estudo teve por objetivo avaliar o efeito de sistemas de manejo do solo baseados em sistemas de preparo, plantas de cobertura e adubacao fosfatada nos estoques de C e N em fracoes fisicas da materia orgânica do solo e na biomassa e respiracao microbiana em um solo cultivado por 11 anos na sucessao soja-milho. O experimento foi iniciado em 1999 em um Latossolo Vermelho argiloso com teor de P adequado para obtencao de 80 a 90 % de rendimentos potenciais de culturas anuais. O delineamento experimental foi o de blocos ao acaso com parcelas divididas, tendo tres sistemas de manejo baseados em preparo do solo e plantas de cobertura (sistema de preparo convencional com milheto, sistema plantio direto com milheto e sistema plantio direto com mucuna-preta) nas parcelas e duas doses de P (0 e 100 kg ha-1 ano-1 de P2O5 na forma de superfosfato triplo, aplicados no sulco de semeadura) nas subparcelas. Amostras de solo foram retiradas no enchimento de graos da soja (marco de 2010), nas camadas de 0-5, 5-10 e 10-20 cm de profundidade, e submetidas ao fracionamento fisico da materia orgânica do solo e a analises microbianas. O sistema plantio direto promoveu estratificacao de C orgânico e N total, enquanto o preparo convencional promoveu distribuicao mais homogenea na camada de 0 a 20 cm de profundidade. A adubacao fosfatada por 11 anos promoveu acumulo de C orgânico e N total em solos com adequada disponibilidade inicial de P, com relacao aquele que nao recebeu adubacao com P, independentemente do sistema de preparo e das plantas de cobertura. O sistema plantio direto apresentou maior estoque de C orgânico e N total, maior C biomassa microbiana e menor respiracao microbiana em relacao ao sistema de preparo convencional, ambos tendo o milheto como planta de cobertura. Quando sob plantio direto, maior estoque de C orgânico e N total, semelhante C biomassa microbiana e maior respiracao microbiana foram obtidos com o milheto como planta de cobertura, em relacao a mucuna. A taxa de conversao do C adicionado pelas culturas em C orgânico do solo foi de 4,0, 8,2 e 14,3 % para sistema de preparo convencional com milheto, sistema plantio direto com milheto e com mucuna, respectivamente.

Adubação nitrogenada suplementar tardia em soja cultivada em latossolos do Cerrado

The objective of this work was to evaluate the effects of nitrogen fertilization at the pre-flowering (R1) and seed filling (R5) stages, on the nodulation and yield of soybean grown in Cerrado Oxisols. The study was performed for seven years in a clayey Typic Haplustox, and for four years in a clayey Rhodic Haplustox, both with established populations of Bradyrhizobium. Fifteen experiments were carried out under conventional and no tillage management systems and the treatments were: standard inoculation (SI) with B. japonicum; SI + 200 kg ha-1 N (urea), split-applied 50% at sowing and 50% at the R1 stage; SI + 50 kg ha-1 N (ammonium nitrate) in R1; SI + 50 kg ha-1 N (ammonium sulfate) in R1; SI + 50 kg ha-1 N (ammonium nitrate) in R5; and SI + 50 kg ha-1 N (ammonium sulfate) in R5. The application of 200 kg ha-1 N harmed nodulation. In only two experiments, the yield responses to late season N applications were significant, with no net economical benefits for the producer. Late nitrogen fertilization on inoculated soybean, grown under Brazilian Cerrados Oxisols, has no economical advantages in any of the management systems evaluated, regardless of the N source applied.

Avaliação do fosfato natural de Gafsa para recuperação de pastagem degradada em latossolo vermelho-escuro

A field experiment was conducted on a Dark-Red Latossol (Haplustox) of the Cerrado of the Federal District, Brazil, to evaluate a coarse-ground Gafsa rock phosphate (CGRP) in the recuperation of a Brachiaria decumbens cv. Basilisk pasture. CGRP was compared with triple superphosphate (TSP) at a P2O5 rate of 100 kg ha-1 both applied by broadcasting. A control treatment without P was included together with two other variables: 1) incorporation of the phosphate with a harrow (with and without) and 2) supplementary fertilization (SF) with Ca, Mg, N, K, S and micronutrients (presence and absence). The response to application of phosphates was only observed with the simultaneous application of SF; incorporation was essential for increasing the efficiency of CGRP; with incorporation, the efficiency of CGRP was equal to that of TSP; without incorporation, TSP was significantly superior to CGRP (p< 0.05).

Distribuição de fósforo no solo em razão do sistema de cultivo e manejo da adubação fosfatada

O sistema de cultivo e o manejo da adubacao fosfatada influenciam a disponibilizacao do P no solo, seu acesso pelas plantas e, por fim, a producao das culturas. Em razao disso, ha necessidade de se avaliar a distribuicao do P no perfil do solo em experimentos de longa duracao, para que se possa compreender o impacto de cada sistema de cultivo e manejo da adubacao nesse processo. Foi utilizado um experimento localizado na Embrapa Cerrados, em Planaltina - DF, em Latossolo Vermelho muito argiloso, com teor de P muito baixo no inicio do experimento, cultivado por 14 anos com as culturas de soja e milho no verao e milheto como planta de cobertura nas seis ultimas safras de inverno, recebendo 80 kg ha-1 ano-1 de P 2O 5 como superfosfato triplo ou fosfato natural reativo, aplicados no sulco de semeadura ou a lanco na superficie, sob sistema de preparo convencional (SPC) ou plantio direto (SPD). Foi avaliada a distribuicao do P em sete camadas de solo (0 a 2,5; 2,5 a 5; 5 a 10; 10 a 20; 20 a 30; 30 a 40; e 40 a 50 cm), utilizando o extrator Bray 1. No 14° ano de cultivo foram utilizados os dados de rendimento de graos de soja. Os resultados foram analisados estatisticamente, para comparacoes quanto a distribuicao do P no perfil do solo e ao rendimento de graos. A distribuicao de P extraivel no solo apos 14 anos de cultivo e influenciada pela fonte e pelo modo de aplicacao do fertilizante fosfatado, ate 10 cm de profundidade no SPD e ate 20 cm de profundidade no SPC. No SPC ha leve gradiente em profundidade, enquanto no SPD ha forte gradiente principalmente para aplicacoes a lanco, sendo os maiores teores de P no perfil analisado encontrados na camada de 0-2,5 cm para os dois modos de aplicacao. O SPD apresenta maiores teores de P ate 10 cm de profundidade, porem menores teores na camada de 10- 20 cm, em comparacao com o SPC. Apesar do efeito do manejo da adubacao fosfatada na distribuicao do P no solo, o rendimento de graos de soja no 14° ano foi alterado apenas pelo sistema de cultivo, tendo o solo sob SPD produzido 15,5 % mais graos do que o SPC.

Drenagem interna como fator de diferenciação de Latossolos do Distrito Federal

The objective of this work was to determine the influence of soil physicohydric characteristics on Oxisols diagnostic attributes. Morphological, chemical, physical, mineralogical and physicohydric attributes were surveyed in profiles of five Latossolos Vermelhos (Rhodic Haplustox, LV) and of five Latosssolos Vermelho-Amarelos (Typic Haplustox, LVA), considered representative of this kind of Oxisols in Distrito Federal, Brazil. Besides the soil diagnostic attributes characterization, the water-table oscillation was monitored using 2.5-m depth observation wells, during one year. The studied Oxisols were considered chemically and physically similar. However, they differed as to morphological and mineralogical characterization, with the presence of concretionary horizons and goethite in the LVA. Goethite stability in this soils was influenced by the water-table oscillation. The presence of concretionry horizons in LVA caused an internal drainage deficiency, which resulted in lower saturated hydraulic conductivity and lower variation of the water-table levels. Therefore, LVA soils show lower agricultural potential than LV ones, in Distrito Federal. Oxisols physicohydric characteristics have little influence on soil diagnostic attributes, except for iron oxides mineralogy, which show increased contents of goethite in low internal drainage conditions.

Transitions to sustainable management of phosphorus in Brazilian agriculture

Brazil’s large land base is important for global food security but its high dependency on inorganic phosphorus (P) fertilizer for crop production (2.2 Tg rising up to 4.6 Tg in 2050) is not a sustainable use of a critical and price-volatile resource. A new strategic analysis of current and future P demand/supply concluded that the nation’s secondary P resources which are produced annually (e.g. livestock manures, sugarcane processing residues) could potentially provide up to 20% of crop P demand by 2050 with further investment in P recovery technologies. However, the much larger legacy stores of secondary P in the soil (30 Tg in 2016 worth over

Relationships between labile soil organic carbon fractions under different soil management systems

40 billion and rising to 105 Tg by 2050) could provide a more important buffer against future P scarcity or sudden P price fluctuations, and enable a transition to more sustainable P input strategies that could reduce current annual P surpluses by 65%. In the longer-term, farming systems in Brazil should be redesigned to operate profitably but more sustainably under lower soil P fertility thresholds.

Gypsum application increases the carbon stock in soil under sugar cane in the Cerrado region of Brazil

The study of labile carbon fractions (LCF) provides an understanding of the behavior of soil organic matter (SOM) under different soil management systems and cover crops. The aim of this study was to assess the effect of different soil management systems with respect to tillage, cover crop and phosphate fertilization on the amount of the LCF of SOM. Treatments consisted of conventional tillage (CT) and no-tillage (NT) with millet as the cover crop and a no-tillage system with velvet bean at two phosphorus dosages. Soil samples were collected and analyzed for organic carbon (OC), C oxidizable by KMnO4 (C-KMnO4), particulate OC (POC), microbial biomass carbon and light SOM in the 0.0-0.05, 0.05-0.10 and 0.10-0.20 m soil layers. The Carbon Management Index (CMI) was calculated to evaluate the impacts of soil management treatments on the quality of the SOM. The different LCFs are sensitive to different soil management systems, and there are significant correlations between them. C-KMnO4 is considered the best indicator of OC carbon lability. In the soil surface layers, the CT reduced the carbon content in all of the labile fractions of the SOM. The use of phosphorus led to the accumulation of OC and carbon in the different soil fractions regardless of the tillage system or cover crop. The application of phosphate fertilizer improved the ability of the NTsystem to promote soil quality, as assessed by the CMI.

Distribuição do carbono orgânico em Latossolo sob manejoda adubação fosfatada em plantio direto no Cerrado

Gypsum is widely used in agriculture in the Cerrado region of Brazil to increase root volume and distribution in the profile of predominantly acidic soils with high aluminium toxicity. The gypsum-induced increase in the root system may be an effective strategy to increase sequestration of atmospheric CO2. However, few studies have investigated the relationship between the use of gypsum and carbon accumulation in the soil under sugar cane. In the present study, total carbon stock (TC) in the soil and its fractions were estimated after four growing seasons of sugar cane under gypsum application. The experiment was arranged in a randomised block design with four replicates and two treatments: control (0Mgha–1) and the technically recommended rate of gypsum application (5Mgha–1). Sugarcane stalk biomass and straw production were evaluated in plant cane and three ratoon crops. Soil samples were taken after evaluation of the third ratoon from seven layers (0–5, 5–10, 10–20, 20–40, 40–60, 60–80 and 80–100cm) to determine organic carbon, TC, particulate carbon (PC) and bulk density. Gypsum increased TC by 5.4 and 4.4Mgha–1 in the 0–100 and 40–100cm layers respectively. The PC pool in the 40–100cm layer was increased by 18.4%, whereas the carbon stock associated with mineral increased by 6.8% with gypsum application. Of the total increase in C stocks resulting from gypsum application, 80% occurred in the 40–100cm layer.