Efeito da Gliricidia sepium sobre nutrientes do solo, microclima e produtividade do milho em sistema agroflorestal no Agreste Paraibano.

Gliricidia sepium é uma leguminosa arbórea que tem sido utilizada em sistemas em aléias no semi-árido nordestino por apresentar bom desenvolvimento em condições de estresse hídrico. Entretanto, há pouca informação disponível sobre o efeito da introdução dessa espécie nos agroecossistemas da região. No presente estudo, objetivou-se avaliar a influência da distância de plantas de Gliricidia sepium sobre características da cultura do milho e do solo e microclima no Agreste Paraibano. O estudo foi realizado no município de Esperança (PB), em área de 0,5 ha, onde, em 1996, foram plantadas fileiras de G. sepium espaçadas 6 m entre si e com 1 m entre as árvores. Nesta área, em 2002, foram delimitadas quatro parcelas de 6 x 8 m e, em cada parcela, foi estabelecido um transeto perpendicular às fileiras de árvores com três posições de amostragem: (1) nas fileiras de árvores (0 m); (2) a 1 m das fileiras de árvores, e (3) a 3 m de distância das fileiras de árvores. O delineamento experimental utilizado foi em blocos casualizados com quatro repetições. A massa seca de folhedo caído embaixo da fileira de árvores foi de 1.390 kg ha-1 e diminuiu, gradativamente, para 270 kg ha-1 a 3 m de distância das árvores. As concentrações de P, K e matéria orgânica leve (MOL) embaixo das árvores foram maiores do que a 1 e 3 m de distância das fileiras. As médias mensais das temperaturas mínimas do ar e do solo embaixo e a 3 m das árvores foram similares. Entretanto, as médias mensais das temperaturas máximas do solo e do ar foram de 6 e 2 °C mais altas a 3 m das árvores, respectivamente, ao longo do período de estudo. A umidade do solo foi significativamente menor embaixo das árvores do que a 1 e 3 m de distância. O milho produziu mais grãos e palha e acumulou mais nutrientes nas posições mais próximas das fileiras de G. sepium

Soil improvement by trees in sub-Saharan Africa

Trees can influence both the supply and availability of nutrients in the soil. Trees increase the supply of nutrients within the rooting zone of crops through (1) input of N by biological N2 fixation, (2) retrieval of nutrients from below the rooting zone of crops and (3) reduction in nutrient losses from processes such as leaching and erosion. Trees can increase the availability of nutrients through increased release of nutrients from soil organic matter (SOM) and recycled organic residues. Roots of trees frequently extend beyond the rooting depth of crops. Research on a Kandiudalfic Eutrudox in western Kenya showed that fast-growing trees with high N demand (Calliandra calothyrsus, Sesbania sesban and Eucalyptus grandis) took up subsoil nitrate that had accumulated below the rooting depth of annual crops. Sesbania sesban was also more effective than a natural grass fallow in extracting subsoil water, suggesting less leaching loss of nutrients under S. sesban than under natural uncultivated fallows. Nutrient release from SOM is normally more dependent on the portion of the SOM in biologically active fractions than on total quantity of SOM. Trees can increase inorganic soil N, N mineralization and amount of N in light fraction SOM. Among six tree fallows of 2- and 3-year duration on an Ustic Rhodustalf in Zambia, inorganic N and N mineralization were higher for the two tree species with lowest (lignin + polyphenol)-to-N ratio (mean = 11) in leaf litter than for the two tree species with highest ratio (mean = 20) in leaf litter. Trees can also restore soil fauna, which are important for SOM and plant residue decomposition. Some agroforestry trees have potential to provide N in quantities sufficient to support moderate crop yields through (i) N inputs from biological N2 fixation and retrieval of nitrate from deep soil layers and (ii) cycling of N from plant residues and manures. The cycling of P from organic materials is normally insufficient to meet the P requirements of crops. Sustained crop production with agroforestry on P-deficient soils will typically require external P inputs

Methane and nitrous oxide emissions from flooded rice fields as affected by water and straw management between rice crops

Rice fields in the tropics can vary in water regime before production of rice on flooded soil, but relatively little is known about the effects of soil water regime and crop residue management between rice crops (i.e., fallow period) on methane (CH4) and nitrous oxide (N2O) emissions during a subsequent rice crop. We measured CH4 and N2O emissions during two cropping seasons in the Philippines from field plots exposed to contrasting treatments during the fallow before land preparation for rice cultivation. The fallow treatments were continuous soil flooding (flooded), soil drying with exclusion of rainfall (dry), soil drying with dry tillage (dry + tillage), and a control with soil drying and wetting from rainfall (dry and wet). All plots were subdivided into removal of all aboveground rice residues from the previous crop (without residue) and retention of standing biomass after harvest of the previous rice crop (with residue). Emitted gas was collected weekly using chambers. Fallow treatments greatly influenced greenhouse gas (GHG) emissions during rice growth. Methane emissions and global warming potential (GWP) in both cropping seasons were highest following the flooded fallow, intermediate following the dry and wet fallow, and lowest following dry and dry + tillage fallows. The GWP was higher with than without residue across all fallow treatments. Nitrous oxide emissions were small during the season, and CH4 emissions contributed more than 90% of the cumulative GWP during the rice crop regardless of fallow and residue management. Soil drying between rice crops in the tropics can reduce CH4 emissions and GWP during the subsequent rice crop

Development and impact of site specific nutrient management in the Red River Delta of Vietnam

Site-specific nutrient management (SSNM) for a more effective use of fertilizers in rice production was developed and validated in the Red River Delta (RRD) of northern Vietnam through a partnership of the Soils and Fertilizers Research Institute (SFRI) and the International Rice Research Institute (IRRI) beginning in 1997. The subsequent dissemination of validated SSNM practices involved collaboration of SFRI and IRRI with the extension system and Plant Protection Division (PPD). We review the development of SSNM in the RRD and estimate the impact of SSNM adoption at the farm level through a survey in 2007 of adopters and nonadopters of SSNM in Ha Nam and Ha Tay provinces. SSNM improved farmers' rice yield by 0.2 t ha-1 in Ha Nam and by 0.34 t ha-1 in Ha Tay in the spring season. SSNM adopters appeared to have improved fertilizer management. SSNM increased net annual income by US$57 ha-1 in Ha Tay and by$78 ha-1 in Ha Nam. Simple projections for the wide application of SSNM throughout the RRD indicate potential annual gains of 228,000 tons of additional unmilled rice. Based on frontier production functions, adopters achieved a slightly higher index of technical efficiency in rice production. SSNM improved farmers' knowledge, attitudes, and skills in rice farming

Soil nitrate and water dynamics in sesbania fallows, weed fallows and maize.

We hypothesized that the integration of trees into agricultural land-use systems can reduce NO3 leaching and increase subsoil N utilization. A field study was conducted on a Kandiudalfic Eutrudox (Ochinga site) and a Kandic Paleustalf (Muange site) in the subhumid highlands of Kenya to measure changes in soil NO3 and water to 200-cm depth for one rainy season in four land-use systems (LUS): (i) planted tree fallow using Sesbania sesban (L.) Merr., (ii) unfertilized maize (Zea mays L.), (iii) weed fallow, and (iv) bare fallow. Subsoil (50-200 cm) NO3-N at the start of the season ranged from 58 to 87 kg ha-1 for the four LUS and two sites. In maize, subsoil NO3-N differed by <5 kg ha-1 between planting and harvest at both sites. In sesbania, subsoil NO3-N decreased by 22 kg ha-1 at both sites, whereas in weed fallow subsoil NO3-N decreased by 26 and 38 kg ha-1 at Ochinga and Muange, respectively. At both sites, subsoil water contents at the start of the season were similar in the four LUS; but at the end of the season, soil water at 100 to 200 cm was significantly lower for sesbania than for maize. Adsorption of NO3 increased with soil depth. Sorbed NO3 at 100 to 200 cm was about 60% in the Kandiudalfic Eutrudox and about 15% in the Kandic Paleustalf. Rotation of maize with either a sesbania fallow or a weed fallow can result in more effective subsoil NO3 and water utilization than maize monoculture