Competition for growth resources between woody and crop species is said to be the main reason for failure of hedgerow intercropping (alleycropping) in semiarid tropics, but the mechanisms of competition are not clearly understood. In this study, conducted in the semiarid highlands of Kenya, soil-water changes and root dynamics were monitored during two rainy seasons from a long-term, replicated, alleycropping experiment. The treatments were (i) maize (Zea mays L.) grown alone, without fertilizer; (ii) maize, without fertilizer, intercropped between hedgerows of leucaena [Leucaena leucocephala (Lam.) de Wit], with hedgerow prunings returned to the alleys; and (iii) maize grown alone, with fertilizer at 40 kg N and 18 kg P ha-1. Available water in 1.25 m of soil depth under alleycropping was lower than with maize alone. Depletion of soil water by hedgerows continued after maize harvest and carried water deficits in alleycropping from one season to the next. Leucaena provided 1.45 Mg ha-1 leaf biomass, which contained 41.6 kg N and 2.5 kg P ha-1; moreover, it added 0.51 Mg ha-1 season-1 of root biomass to the soil, equivalent to 7 kg N and 0.2 kg P ha-1. Therefore, N contributed through the alleycropping system was equivalent to the recommended fertilizer level; the system, however, did not meet the P requirements of the crop. Maize did not respond to fertilizer in both seasons, and the alleycropped maize yielded lower than the unfertilized maize.
Tag: hedgerow intercropping
Agronomic and economic appraisal of alley cropping with Leucaena diversifolia on an acid soil in the highlands of Burundi
Although alley cropping has been shown elsewhere to permit continuous cropping, it has not been widely tested in the highlands of east and central Africa where it has the additional potential of controlling soil erosion. The effect of four rates (0, 30, 60 and 90 kg N ha1) of inorganic N on the performance of alley cropping using Leucaena diversifolia as the hedgerow species was studied in the central highlands of Burundi. Significant increase in maize yield (average of 26%) due to alley cropping was only first realised in 1992, three years after the commencement of the trial. In 1993, the average yield advantage of the alley cropping plots was 21%. The prunings augmented the response of maize yield to inorganic N in 1992 and 1993. Compared with the control, economic benefits over the five-year period for all the treatments were negative.
Food-crop-based production systems as sustainable alternatives for Imperata grasslands?
Purely annual crop-based production systems have limited scope to be sustainable under upland conditions prone to infestation by Imperata cylindrica if animal or mechanical tillage is not available. Farmers who must rely on manual cultivation of grassland soils can achieve some success in suppressing Imperata for a number of years using intensive relay and intercropping systems that maintain a dense soil cover throughout the year, especially where leguminous cover crops are included in the crop cycle. However, labour investment increases and returns to labour tend to decrease in successive years as weed pressure intensifies and soil quality declines. Continuous crop production has been sustained in many Imperata-infested areas where farmers have access to animal or tractor draft power. Imperata control is not a major problem in such situations. Draft power drastically reduces the labour requirements in weed control. Sustained crop production is then dependent more solely upon soil fertility management. Mixed farming systems that include cattle may also benefit from manure application to the cropped area, and the use of non-cropped fallow areas for grazing. In extensive systems where Imperata infestation is tolerated, cassava or sugarcane are often the crops with the longest period of viable production as the land degrades. On sloping Imperata lands, conservation farming practices are necessary to sustain annual cropping. Pruned tree hedgerows have often been recommended for these situations. On soils that are not strongly acidic they may consistently improve yields. But labour is the scarcest resource on small farms and tree-pruning is usually too labour-intensive to be practical. Buffer strip systems that provide excellent soil conservation but minimize labour have proven much more popular with farmers. Prominent among these are natural vegetative strips, or strips of introduced fodder grasses. The value of Imperata to restore soil fertility is low, particularly compared with woody secondary growth or Compositae species such as Chromolaena odorata or Tithonia diversifolia. Therefore, fallow-rotation systems where farmers can intervene to shift the fallow vegetation toward such naturally-occurring species, or can manage introduced cover crop species such as Mucuna utilis cv. cochinchinensis, enable substantial gains in yields and sustainability. Tree fallows are used successfully to achieve sustained cropping by some upland communities. A variation of this is rotational hedgerow intercropping, where a period of cropping is followed by one or more years of tree growth to generate nutrient-rich biomass, rehabilitate the soil, and suppress Imperata. These options, which suit farmers in quite resource-poor situations, should receive more attention.
Productivity of annual cropping and agroforestry systems on a shallow alfisol in semi-arid India
An experiment was conducted at ICRISAT Center, Patancheru, India from June 1984 to April 1988 on a shallow Alfisol to determine whether the productivity of annual crop systems can be improved by adding perennial species such as Leucaena leucocephala managed as hedgerows. Except in the first year, crop yields were suppressed by Leucaena due to competition for moisture. The severity of competition was high in years of low rainfall and on long-duration crops such as castor and pigeonpea. Based on total biomass, sole Leucaena was most productive; even on the basis of land productivity requiring both Leucaena fodder and annual crops, alley cropping had little or no advantage over block planting of both components. Application of hedge prunings as green manure or mulch on top of 60 kg N and 30 kg P2O5ha1 to annual crops did not show any benefit during the experimental period, characterized by below average rainfall. Indications are that (i) alley cropping was beneficial in terms of soil and water conservation with less runoff and soil loss with 3 m alleys than with 5.4 m alleys, and (ii) root pruning or deep ploughing might be effective in reducing moisture competition.
Tree-crop Interactions for Below-ground Resources in Drylands: Root Structure and Function
An experiment was conducted at ICRISAT Center, Patancheru, India from June 1984 to April 1988 on a shallow Alfisol to determine whether the productivity of annual crop systems can be improved by adding perennial species such as Leucaena leucocephala managed as hedgerows. Except in the first year, crop yields were suppressed by Leucaena due to competition for moisture. The severity of competition was high in years of low rainfall and on long-duration crops such as castor and pigeonpea. Based on total biomass, sole Leucaena was most productive; even on the basis of land productivity requiring both Leucaena fodder and annual crops, alley cropping had little or no advantage over block planting of both components. Application of hedge prunings as green manure or mulch on top of 60 kg N and 30 kg P2O5ha1 to annual crops did not show any benefit during the experimental period, characterized by below average rainfall. Indications are that (i) alley cropping was beneficial in terms of soil and water conservation with less runoff and soil loss with 3 m alleys than with 5.4 m alleys, and (ii) root pruning or deep ploughing might be effective in reducing moisture competition.
Adoption potential of rotational hedgerow intercropping in the humid lowlands of Cameroon
Shifting cultivation in the humid lowlands of Cameroon has been associated with declining soil fertility resultingin low yields of food and tree crops. Agroforestry and improved fallow systems such as hedgerow intercropping canplay an important role in improving sustainable production on farmers’ fields. Between 1988 and 1993 theInternational Centre for Research in Agroforestry Humid Lowlands of West Africa Programme (ICRAF-HULWA) inCameroon evaluated the conventional hedgerow intercropping and, more recently (1994–8), rotational hedgerowsystems. Farmer adoption has remained low. Based on continued monitoring of on-farm trials and a socioeconomicsurvey, three main reasons why farmers do not easily adopt the innovation were identified. Firstly, contrary toexpectations, farmers indicated that land availability is not a problem and that they can acquire more land in thevillage if there is a need. Secondly, in the lowlands of Cameroon, soil erosion is not a major concern of farmers.Thirdly, farmers in the study zone do not feel that soil fertility is a major problem and are thus hesitant to invest infertility management. Furthermore, farmers seem to be concerned about issues such as lack of marketing opportunitiesand shortage of cash to pay for health care and education, rather than the decline in soil fertility. However, recentexperience with more flexible design and management of hedgerow intercropping and more targeted promotion ofthe technology has shown a growing interest of farmers to plant tree fallows. Consequently, further research shouldfocus on diversification of the output of rotational hedgerow systems. The promotion of rotational hedgerow systemsshould target sites where farmers perceive land shortage and poor soils to be major problems