Using mulch to tackle the problems of soil fertility depletion and weed management may contribute to improved crop productivity in most tropical and subtropical developing countries. We conducted a field study on slope plots on Ishigaki Island, Japan, to assess the effect of zero tillage and cover cropping on soil fertility, weed control and crop productivity under a legume-cereal (hairy vetch Vicia villosa Roth and maize Zea mays L., respectively) relay cropping system. The six studied treatments consisted of hairy vetch (HV) or weed fallow followed by nil or conventional tillage with or without fertilization. Weed biomass in zero tillage treatments was five-fold smaller than in the tilled plots. The release of nitrogen (N) from hairy vetch biomass contributed to the total N input in the soil-plant system and favored greater availability and uptakes of N and P by maize crop in hairy vetch treatments than in natural fallow treatments. In the present study, hairy vetch with conventional tillage system obtained the best maize production. The favorable soil environment with the "hairy vetch-zero tillage-half recommended fertilization" system induced a maize grain yield 0.60 t ha −1 higher compared with natural fallow with recommended fertilization. Although not significant, maize yield with hairy vetch followed by zero tillage and nil fertilization was 5% greater than yields scored with natural fallow + recommended fertilization. The above results suggest that hairy vetch cover cropping combined with zero tillage could offer opportunities for low external input farmers to substantially increase and sustain crop productivity; thereby contributing to the intensification of low-input farming systems.
Hairy vetch (Vicia villosa), as a winter cover crop, can be used to suppress weeds in subtropical regions, as well as temperate regions. Information on the potential biomass growth of hairy vetch for weed control and nutrient accumulation is not available in subtropical regions. Hairy vetch was sown in November 2004, and October, November, and December 2005. The wide‐ranging cultivation period of hairy vetch indicated that it could be used in various cropping systems. It showed a higher biomass and nutrient accumulation when grown in subtropical Okinawa, Japan. Moreover, the biomass, and fixed carbon and magnesium (Mg) uptake in the above‐ground parts of hairy vetch were found to be the highest in late May, with the highest nitrogen (N), potassium, and calcium uptake in mid‐April and phosphorus (P) uptake in late March. Meanwhile, in the underground parts of the plant, they were highest in early May, except for the P and Mg uptake, which were highest in mid‐April. According to the sowing date, the biomass and nutrient uptake of hairy vetch that was harvested in February were higher when sown in October. Similarly, when harvested in March, the biomass and nutrient uptake were higher when sown in October or November. In April, they were higher when sown in November or December. Hairy vetch has the potential to effectively suppress weeds in the winter and the spring seasons related to its sufficient biomass during the growing seasons. However, both the sowing and harvesting times of hairy vetch should be considered with reference to the cropping system; the subsequent crop will be sown to meet the N requirement.
Weeds emerge throughout the year in agricultural fields in subtropical regions. The weed suppression and improved soil fertility resulting from a living mulch of hairy vetch were investigated. Hairy vetch was sown in October and in December 2006. The fallow condition was without the sowing of hairy vetch, with the weeds allowed to grow naturally. The biomass of the top parts (BOT) of hairy vetch increased from February to April and then decreased in May on both sowing dates. The BOT of hairy vetch sown in October was significantly higher in February, March, and April than that sown in December. Hairy vetch sown in October and harvested from February to April varied from 372–403 × 10−3 kg m−2, with weed suppression percentages of 62.8% in comparison with the fallow plots. The fixed C, N, P, and mineral uptake of hairy vetch showed similar patterns to its biomass. The nitrate (NO3‐N) content increased from February to May for the soils in the October and December plots, in contrast to the fallow plots. Moreover, the NO3‐N and available N of the October and December soils sampled from February to May were higher than that of the fallow soils. In subtropical agriculture, hairy vetch should be sown in October in order to achieve a higher biomass for suppressing weeds effectively and improving the soil fertility, mainly N.
In the Sudan Savanna of West Africa, Plinthosols with a petroplinthic or pisoplinthic horizon at ≤ 50 cm from the surface comprise the major soils. Because these horizons limit the rooting volume and water and nutrient storage capacities of the soils, they should be a major cause of decreased crop yield in the Sudan Savanna. However, the local distribution of Plinthosols is not precisely known, and the relationships between soil classes, effective soil depth, and crop yield, which are considered to be closely related to each other on the Plinthosol soils, are not fully understood. To clarify these relationships, we first reassessed the soil toposequence on a slope at the Institute of Environment and Agricultural Research Saria station in Burkina Faso using the current World Reference Base soil classification system. We then determined the relationships between soil classes and sorghum yield and between the effective soil depth and yield. We also assessed whether ground penetrating radar could predict the position of a petroplinthic horizon. We found (1) that Pisoplinthic Petric Plinthosols were found at the upper slope, Petric Plinthosols were found at the middle slope, and Ferric Lixisols were found at the lower to toe slope; (2) that sorghum yield was significantly larger at the Ferric Lixisols, then at the Petric Plinthosols, and lower at the Pisoplinthic Petric Plinthosols; (3) that sorghum yield was proportional to the effective soil depth at which upper boundary of petroplinthic horizon was found (n = 26, R 2 = 0.78*** exclusion of waterlogged soil); and (4) that ground penetrating radar could predict the effective soil depth and the position of petroplinthic horizons (n = 4, R 2 = 0.99**), suggesting that we could roughly but easily predict sorghum yield and local distribution of Plinthosols having a petroplinthic horizon using GPR. These results may enable us to take more account of the inherent soil conditions when studying soil and water conservation, fertilization methods, and crop breeding, all of which are crucial if sustainable agricultural methods are to be achieved in the Sudan Savanna.
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