Rômulo Simões Cezar Menezes

Land quality changes following the conversion of the natural vegetation into silvo-pastoral systems in semi-arid NE Brazil

The presence of trees in grasslands frequently results in resource islands of higher soil quality. Therefore, some native trees are often preserved or agroforestry species are interplanted when land is cleared for pasture. We evaluated soil quality changes associated with the conversion of a native thorn forest (caatinga) into silvo-pastoral systems in semiarid NE Brazil. Soil nutrients, organic matter, microbial biomass and soil enzymes under native caatinga, the canopy of two preserved native (Ziziphus joazeiro and Spondias tuberosa) and one introduced tree species (Prosopis juliflora), and under a planted pasture of Cenchrus ciliaris were compared. The two preserved tree species maintained high nutrient and organic matter contents and high biological activity levels not only relative to the grass but also relative to the native caatinga. The non-deciduous Z. joazeiro was more effective than the deciduous S. tuberosa, and enriched surface soils by 100 mg P kg-1. The complete replacement of natural caatinga with C. ciliaris pasture or a C. ciliaris–P. juliflora silvopastoral system had, after 14 years, decreased microbial biomass C and N contents, and ß-glucosidase activity, but did not affect soil nutrient or organic matter status. The biological activity under the trees of the tree-grass association was greater than under grass alone, although P. juliflora did not maintain higher nutrient or organic matter levels. The search for indigenous alternatives to the main agroforestry species may provide viable alternatives for improved land management and the conservation of biodiversity. Microbiological and biochemical parameters responded more readily to changes in land management than chemical fertility indices. They are important indices for the impact of vegetation changes and its associated land quality changes.

Mineralização de N após incorporação de adubos orgânicos em um Neossolo Regolítico cultivado com milho

Farms within the Agreste region of Paraiba often do not have sufficient animal manure to maintain the fertility of the soil and green manures, such as prunings of Gliricidia sepium, are an alternative to increase nutrient supply. The objectives of this work were to compare N mineralization dynamics following additions of cattle manure or Gliricidia sepium prunings to a Entisol, under field and laboratory conditions. In the field experiment, three treatments were established: addition of 20 t ha-1 of cattle manure; addition of 15 t ha-1 of green branches of Gliricidia, or a control without any addition. Maize was sown immediately after the additions. Soil N mineralization in the field was measured in situ during 120 days, in the 0-15 cm layer. Nitrogen uptake by corn was also recorded. Soil N mineralized in the laboratory was followed during 56 days in samples from the 0-15, 15-30 e 30-60 cm layers. Samples from the 0-15 cm layer received manure and Gliricidia at rates equivalent to those in the field. An average of 74 kg ha-1 of N were mineralized in the field until harvest (120 days). In the laboratory, Gliricidia additions hastened net N mineralization while cattle manure induced net N immobilization during 14 days.

Caatinga, the Brazilian dry tropical forest: can it tolerate climate changes?

Our review focuses on the projections of climate change in the Brazilian semiarid region, the Caatinga, based on recent publications about global climate change and biology. We found several vulnerable points in the initial estimates, the main one being that the data were collected and analyzed without a multidisciplinary knowledge. This review discusses several studies that show the current knowledge in many semiarid regions around the world. Some of these studies argue for the increase in vegetation greenness responses even under severe and prolonged drought, based on the high resilience the Caatinga native species show under severe drought conditions over the years. Additionally, we include in this review recent data produced by our group on key ecophysiological variables under drought conditions. We also show successful examples of deforested areas recovery in the semiarid region of the Central America. It is critical that the recovery of semiarid areas is coupled with the implementation of socio-environmental policies, engaging the local population and providing subsidies for life wealth improvement. These are key aspects for a long-term recovery and conservation of the Brazilian dry tropical forest.

Mudanças na fertilidade de um Neossolo Regolítico após seis anos de adubação orgânica

The objective of this study was to evaluate the effects of application of six years of organic manure with animal and/or cover crop on the fertility of an Entisol. Treatments were: 1) animal manure (15 t ha-1); 2) use of Crotalaria juncea L. as a cover crop; 3) fertilization with half (7.5 t ha-1) of the usual doses of animal manure combined with C. juncea L. as a cover crop; and 4) control plots without application. The study was conducted from 1996 to 2003, but no fertilization was done in 1998 and 1999, due to severe droughts. At the end of 2003, soil samples from two depths (0-20 and 20-40 cm) were collected and analyzed to determine the nutrient concentrations. The annual fertilization with animal manure, with or without C. juncea, increased soil extractable P, K, Mg and B in both soil layers, but increased soil organic carbon, total N, total P, and Zn only in the 0-20 cm layer. The cultivation and incorporation of C. juncea had no consistent effect on soil fertility. The results have shown that the application of lower doses of manure combined with C. juncea maintained soil fertility at levels comparable to application of 15 t ha-1 of animal manure.

Maize growth and soil nitrogen availability after fertilization with cattle manure and/or gliricidia in semi-arid NE Brazil

Cattle manure is used as fertilizer by farmers in northeastern Brazil. However, the manure is insufficient to fertilize all cropping areas and is usually of low quality and may immobilize N. The use of Gliricidia sepium as green manure could increase the amount and quality of organic fertilizers. However, the high-quality biomass of this legume is valued as forage and may also decompose too quickly and cause nitrogen (N) leaching. This study aimed to identify efficient management practices for cattle manure and Gliricidia to improve N uptake and crop productivity in semi-arid NE Brazil. For this, we conducted three experiments. In the greenhouse, we evaluated maize growth and N uptake after application of Gliricidia and/or cattle manure under different soil moisture conditions. A litterbag field experiment evaluated the decomposition dynamics of Gliricidia or manure. Finally, a field experiment tested the effects of mixing and/or splitting Gliricidia and manure on maize productivity and N uptake. In the greenhouse, maize dry matter production and N uptake and apparent N recovery from fertilizers were significantly greater in treatments with higher proportions of Gliricidia, but mainly under high soil moisture conditions. The litterbag experiment showed that Gliricidia indeed decomposed twice as fast as cattle manure, that decomposition was up to 2.5 times faster when the materials were incorporated rather than surface applied, and also that N release was more synchronized to maize demand when fertilizers were split in two applications. In the field experiment, we observed that both mixing cattle manure and Gliricidia and splitting the application in two increased in maize productivity up to 350%.

Ciclagem de nutrientes via precipitação pluvial total, interna e escoamento pelo tronco em sistema agroflorestal com Gliricidia sepium

The nutrients in rainwater that reach the soil by throughfall or stemflow may represent significant nutrient fluxes in agroforestry systems with low external input. However, there is no information about these processes in agroecosystems of semi-arid northeastern Brazil. This study was conducted in an alley cropping system with Gliricidia and maize in Esperanca, PB, Brazil. The objectives of the study were to quantify: (a) the proportion of rainfall that reaches the soil as throughfall or stemflow and the amount intercepted by the tree canopy; and (b) the input of N, P and K to the soil as throughfall, stemflow and direct rainfall water. Four plots were established in the experimental area and throughfall water collectors were placed at a distance of 0.50 m from the tree trunks. Stemflow water was collected in each plot using collars around the tree trunks that conducted the water to collectors while four collectors were installed in adjacent areas without trees to collect rainfall water. Of the total rainfall in 2004, 67 % reached the soil as throughfall, 0.74 % as stemflow and 32 % was intercepted by tree canopies. N and P concentrations were similar in throughfall and stemflow water samples, but these were around 300 % greater than those in rainfall water. The K concentration in stemflow water was 100 and 600 % greater than in samples from throughfall and rainfall, respectively. On average, N, P, and K inputs to the soil were 5, 1 and 24 kg ha-1 in rainfall water; 9, 2 and 62 kg ha-1 in throughfall water; and 0.12, 0.02 and 1 kg ha-1 in stemflow water, respectively. The results demonstrate the importance of agroforestry for the sustainability of agricultural systems with low external input in semi-arid NE Brazil.

Nodulação e fixação de nitrogênio por forrageiras da caatinga cultivadas em solos do semiárido paraibano

A fixacao biologica de nitrogenio foi avaliada em jureminha (Desmanthus pernambucanus), orelha-de-onca (Macroptilium martii) e feijao-de-rolinha (Macroptilium lathyroides) cultivados em solos do semiarido da Paraiba, em vasos sem e com esterco bovino. Foram determinados o numero e a biomassa de nodulos, os teores e as proporcoes de nitrogenio (N) fixado (percentual de nitrogenio da planta derivado do ar-%Ndda), pelo metodo da abundância natural, utilizando-se o capim-buffel como planta controle. As leguminosas tiveram nodulacao abundante, nos tres solos e na ausencia ou presenca de esterco, salvo quando cultivadas em Neossolo Fluvico sem adubacao. A adubacao com esterco aumentou o numero e a biomassa de nodulos. A fixacao biologica de nitrogenio foi alta nas tres especies, nos tres solos: na maioria das plantas, os valores superaram 50%, chegando a 85%. Esses dados permitem estimar a capacidade de fixacao das especies no campo em 10 a 30 kg ha-1 de N, considerando as densidades de plantio e produtividade usuais. As menores %Ndda e quantidades fixadas foram encontradas nas plantas cultivadas em Neossolo Regolitico e aumentaram com a adicao de esterco. Entre as especies testadas, a fixacao biologica de nitrogenio foi menos importante para D. pernambucanus. Nenhum dos parâmetros de nodulacao avaliados (numero, biomassa e biomassa/nodulo) explicou as proporcoes nem as quantidades de nitrogenio fixadas pelas plantas.

Residual effect of organic fertilization on maize yield in an agroforestry system

The objective of the present study was to evaluate, during a period of two years, the residual effects of organic fertilization with animal manure or gliridicia prunings on the fertility of soil and on productivity and nutrient accumulation by maize cultivated either isolated (SA) or intercropped within alleys of gliricidia (CA). The study was conducted during 2006 and 2007 in the Centro Agroecologico Sao Miguel, headquarters of the NGO AS-PTA, in Esperanca, PB, Brazil. The experiment was established in a split-plot design, arranged in randomized blocks, with the type of cropping system (SA or CA) as the main treatments and the organic fertilization (animal manure, gliricidia prunings or control plots) as the secondary treatments, with four replications. The organic fertilization with animal manure led to a residual effect increasing maize productivity during the two years, but the fertilization with gliricidia prunings had no residual effect. The residual effect on maize productivity was more pronounced in the SA plots, compared to the plots with gliricidia alleys (CA). Probably, the lower residual effect within the CA system was due to the competition between maize and gliricidia for resources (nutrients, water and light), which indicates the need for higher rates or more frequent fertilizer applications in these systems. The contents of P, K, Ca and Mg in the soil was higher in the plots that received animal manure within both types of cropping systems.

15 N natural abundance of non-fixing woody species in the Brazilian dry forest (caatinga)

Foliar δ15N values are useful to calculate N2 fixation and N losses from ecosystems. However, a definite pattern among vegetation types is not recognised and few data are available for semi-arid areas. We sampled four sites in the Brazilian caatinga, along a water availability gradient. Sites with lower annual rainfall (700 mm) but more uniform distribution (six months) had δ15N values of 9.4 and 10.1 ‰, among the highest already reported, and significantly greater than those (6.5 and 6.3 ‰) of sites with higher rainfall (800 mm) but less uniform distribution (three months). There were no significant differences at each site among species or between non-fixing legume and non-legume species, in spite of the higher N content of the first group. Therefore, they constitute ideal reference plants in estimations of legume N2 fixation. The higher values could result from higher losses of 15N depleted gases or lower losses of enriched 15N material.

Land cover changes and greenhouse gas emissions in two different soil covers in the Brazilian Caatinga

The Caatinga biome covers an area of 844,453km(2) and has enormous endemic biodiversity, with unique characteristics that make it an exclusive Brazilian biome. It falls within the earths tropical zone and is one of the several important ecoregions of Brazil. This biome undergoes natural lengthy periods of drought that cause losses in crop and livestock productivity, having a severe impact on the population. Due to the vulnerability of this ecosystem to climate change, livestock has emerged as the main livelihood of the rural population, being the precursor of the replacement of native vegetation by grazing areas. This study aimed to measure GHG emissions from two different soil covers: native forest (Caatinga) and pasture in the municipality of São João, Pernambuco State, in the years 2013 and 2014. GHG measurements were taken by using static chamber techniques in both soil covers. According to a previous search, so far, this is the first study measuring GHG emissions using the static chamber in the Caatinga biome. N2O emissions ranged from -1.0 to 4.2mgm(-2)d(-1) and -1.22 to 3.4mgm(-2)d(-1) in the pasture and Caatinga, respectively, and they did not significantly differ from each other. Emissions were significantly higher during dry seasons. Carbon dioxide ranged from -1.1 to 14.1 and 1.2 to 15.8gm(-2)d(-1) in the pasture and Caatinga, respectively. CO2 emissions were higher in the Caatinga in 2013, and they were significantly influenced by soil temperature, showing an inverse relation. Methane emission ranged from 6.6 to 6.8 and -6.0 to 4.8mgm(-2)d(-1) in the pasture and Caatinga, respectively, and was significantly higher only in the Caatinga in the rainy season of 2014. Soil gas fluxes seemed to be influenced by climatic and edaphic conditions as well as by soil cover in the Caatinga biome.