Effect of landfill leachate on cereal nutrition and productivity and on soil properties.

Landfill leachates carry nutrients, especially N and K, which can be recycled in cropping systems. We applied doses of landfill leachate (0 [Control], 32.7, 65.4, 98.1, and 130.8 m3 ha-1 ) three times in 2008 and three times in 2009 on a clay Rhodic Kandiudult soil. In 2009, black oat (Avena strigosa L.) and corn (Zea mays L.) were cropped in succession and assessed for concentration of nutrients in leaves and for shoot biomass and grain yield, respectively. As a positive control, an additional treatment with urea (120 kg ha-1 of N) was studied in corn. Soil was sampled at four depths (down to 60 cm) in three sampling dates to assess chemical and biochemical properties. Concentration of nutrients in leaves, oat biomass (8530?23,240 kg ha-1), and corn grain yield (4703-8807 kg ha-1 ) increased with increasing doses of leachate. There was a transient increase in the concentration of nitrate in soil (3-30 mg kg-1), increasing the risk of N losses by leaching at doses above 120 kg ha-1 N, as revealed by an estimated N balance in the cropping system. Sodium and K in soil also increased with increasing doses of leachate but decreased as rainfall occurred. The activity of dehydrogenase decreased about 30% from the control to the highest dose of leachate and urea, suggesting an inhibitory effect of mineral N on microbial metabolism. Landfill leachate was promising as a source of N and K for crop productivity and caused minor or transient effects on soil properties.

A review of maize-beans and maize-cowpea intercrop systems in the semiarid Northeast Brazil.

Fifty-one experiments on maize -beans and 34 on maize-cowpea intercropping systems conducted mostly in semiarid Northeast Brazil were analysed to get an understanding of the performance of these intercrops in terms of their productivity as well as stability. Both the intercrop systems produced higher yields over their respective sole crops under a wide range of agroclimates; the average advantage with maize-beans was 32%, while that from maize-cowpea was 41%. The optimum row proportion for maize-beans was one maize: three beans, requiring 59% of sole crop maize population and 75% sole bean population. In maize-cowpea, alternate rows or one maize: two cowpea arrangement with about 50% of sole maize density and 100% of sole cowpea population seemed to be optimum. The intercrops failed less frequently compared to sole crops to meet specified incomes or yields. Sorghum seemed to be a good alternative to the traditional cereal because of its improved and consistent performance. Future research needs are discussed for further yield improvement in these two intercrop system.s

Especificidade na infecção de raízes por Azospirillum spp. em plantas com via fotossintética C3 e C4.

Resultados anteriores sobre a especificidade hospedeira na infecção de gramíneas com Azospirillum spp foram confirmados no presente trabalho, com maior número de espécies. No solo ocorreram as duas espécies de Azospirillum - A. brasilense e A. lipoferum - e, ainda estirpes denitrificantes (nir+) e não denitrificantes (nir-). Os isolamentos de raízes esterilizadas de cereais de clima temperado com via fotossintética C3 (trigo, cevada, aveia, e centeio), foram predominantemente da espécie. A. brasilense; e os de raízes esterilizadas de gramíneas tropicais com via C4 foram predominantemente da espécie A. lipoferum. Em ambos os casos parece que as plantas, especialmente as C3, apresentam seletividade para estirpes não denitrificantes. A única exceção nestas observações foi a cana-de-açúcar, que se comportou como os cereais temperados. Por outro lado, a tiririca, uma Cyperacea com via C4, foi infectada por A. lipoferum, como as gramíneas com via C4.