Soil infertility is the major cpnstraint to agricultural production and food security in Ethiopian Highland farming systems. Farmers have very limited capacity to invest in fertilizers or soil conservation measures. As a result, yields are low and many farmers are forced to put fallow and marginal lands into production to meet their food needs. A potential solution for fertility maintenance is to use farm-generated resources such as crop residues, farmyard manure and legumes that are intercropped as green manure or used for biomass transfer. However, there are limitations to the amount of biomass these system can produce. There are also competing demands for these resources because they are used as livestock feed, cooking fuel and to generate income.
Tag: cover crops
Nitrogen supply from rotational or spatially zoned inclusion of Leguminosae for sustainable maize production on an acid soil in Indonesia
On acid upland soils in the humid tropics, the combination of high leaching rates and shallow rooted crops may lead to low efficiencies of N use. Sustainability of crop production in this zone depends on either large amounts of external inputs, or on maximising efficiency of the use of local as well as small amounts of external resources. Additional sources of soil organic matter can be obtained by including leguminous cover crops in a rotational system or by spatially zoned systems, with a permanent presence of trees. In view of the high leaching rates, spatially zoned systems with deep-rooted trees may be more effective.Long term soil fertility experiments were started on an Ultisol in Lampung, Sumatera, Indonesia. Data are discussed here for cropping systems based on rotations of maize and leguminous cover crops and for hedgerow intercropping systems (spatially zoned). Maize production in rotations with leguminous cover crops was highest when Mucuna pruriens, Calopogonium mucunoides or C. caeruleum were used. Compared to a grass-weed fallow control, an additional grain yield of 0.5–1 t ha-1 could be obtained. The efficiency of using biomass N was about 0.8 times that of using urea in two split applications. The best results for hedgerow intercropping, a maize yield increase of 1t ha-1 over a control, were obtained with the local tree species Peltophorum dasyrachis
Root distribution of leguminous cover crops in the humid tropics and effects on a subsequent maize crop
Leguminous cover crops can be used in the humid tropics to increase the production of subsequent food crops, through effects on nitrogen availability in the soil, suppression of weeds and/or changes in soil physical conditions. Nodulation, total root and shoot mass and depth of root development are important characteristics of cover crops. Root development of several cover crops is described here for two sites with acid soils, in S.E. Nigeria and S. Sumatera, Indonesia. Short-lived annual species have a higher shoot: root ratio than perennial species. Mucuna pruriens utilis had the most shallow root system, but good nudulation and, through its fast growth, it was best insuppressing weeds (in a 4-month period). Mucuna and Crotalaria juncea gave the best effect on a subsequent maize crop in an experiment on a dark grey alluvial soil in Malang, E. Java, Indonesia. Apart from being a source of N, the cover crops also had a positive effect on subsequent maize growth by increasing water storage in the soil and by improving root development of maize.
Effect of field establishment methods on root-knot nematode (Meloidogyne spp) infection and growth of Sesbania sesban in western Kenya
Pot studies indicated that root-knot nematode (Meloidogyne javanica) infection reduces sesbania (Sesbania sesban) growth and planting methods modify the nematode damage, but their effects on sesbania biomass production at the field scale are not known. A field study was conducted in western Kenya for 2 yr, comparing direct seeding of sesbania with transplanting of bare-rooted seedlings in pure stands, with and without nematicide application in the field and in the nursery. In moist conditions, neither planting method nor nematicide had any influence on seedling survival and early growth. When early season rainfall was low and erratic, transplanted seedlings survived and grew better than seedlings from direct sowing, and nematicide application in the field and/or nursery improved seedling survival. Direct seeded sesbania had significantly less nematode galling and smaller nematode populations in the roots than transplanted sesbania. Both the establishment methods produced similar quantities of biomass, but direct seeded sesbania produced significantly greater biomass than the transplanted crop, if seedlings were already infected with nematodes in the nursery. Nematode infection on average reduced total sesbania biomass by 19%. Where sesbania cover crops have to be established by transplanting for socio-economic reasons, it is essential to use healthy seedlings free from nematodes for a good plant stand and early growth. Nematode-free seedlings can be produced on farms by at least one month of solarization of seedbeds. Neither field establishment method, nor nematicide application altered the soil nematode populations over a 12-month period. This means that the potential threat of increased Meloidogyne populations to nematode-susceptible crops following sesbania cover crops remains the same irrespective of how sesbania is established.
The effect of cattle grazing on soil physical and chemical properties in a silvopastoral system in the Peruvian Amazon
In a six-year-old peach palm (Bactris gasipaes) plantation, centrosema (Centrosema macrocarpum), a leguminous forage plant, was established as a cover crop which was eventually grazed. This experiment was designed to monitor probable changes in soil physical and chemical properties and measure peach palm fruit production and live-weight gain of cattle grazing this silvopastoral system. The experiment was installed on land that was previously cleared by a D7 bulldozer having a straight blade that mixed the thin layer of topsoil with the acid subsoil (20–40 cm) and severely compacted the soil. The results demonstrated that the centrosema cover crop reduced soil bulk density, increased water infiltration rates and reduced mechanical resistance. In general soil physical properties were improved with the use of Centrosema as forage and cover crop. Soil acidity and aluminum saturation decreased considerably, while potassium concentrations increased. Calcium and magnesium concentrations decreased over time as these minerals were stored in the pasture biomass, translocated to fresh peach palm fruits and/or exported to animals. A strong competition for nutrients was observed between the peach palm plants and Centrosema. The low production of peach palm fruits was in response to mechanized land clearing during initial establishment of the plantation, and also probably due to deficits of N, P, K, Ca and Mg in the soil instead of being a consequence to the presence of cattle. The average increase in live-weight gains of the cattle was at a rate of 445 g/animal/day during the four-years of the study. Such an increase is substantially greater than those registered in the area under traditional grazing systems used in the region.
Productivity of intensified crop-fallow rotations in the Trenbath model
Management of crop—fallow rotations should strike a balance between exploitation, during cropping, and restoration of soil fertility during the fallow period. The ‘Trenbath’ model describes build-up of soil fertility during a fallow period by two parameters (a maximum level and a half-recovery time) and decline during cropping as a simple proportion. The model can be used to predict potential crop production for a large number of management options consisting of length of cropping period and duration of fallow. In solving the equations, the model can be restricted to ‘sustainable’ systems, where fallow length is sufficient to restore soil fertility to its value at the start of the previous cropping period. The model outcome suggests that the highest yields per unit of land can be obtained by starting a new cropping period after soil fertility has recovered to 50–60% of its maximum value. This prediction is virtually independent of the growth rate of the fallow vegetation. The nature of the fallow vegetation (natural regrowth, planted trees, or cover crops) mainly influences the crop yield by modifying the required duration of fallow periods. Intensification of land use by shortening fallow periods will initially increase returns per unit land at the likely costs of returns per unit labor. When fallows no longer restore soil fertility to 50% of the maximum, overall productivity will decline both per unit land and per unit labor, unless external inputs replace the soil fertility restoring functions of a fallow