A simple model is presented for calculating the rooting depth of a crop or crop combination required to intercept leaching nutrients for different climatic and soil conditions. Important parameters in this model are the amount of water moving through the soil, which depends on excess of rainfall over evapotranspiration, and the apparent adsorption constant, which depends on the nutrient and soil type involved. Calculations for three time patterns of nutrient supply in relation to nutrient demand show moderate effects of the degree of synchronization on rooting depth required if a high interception fraction is desired. In shifting cultivation systems a deep-rooted fallow vegetation can recover nutrients leached to the subsoil during the cropping phase. The simple leaching model can indicate the combinations of climate zone and apparent adsorption constant for which such interception is possible. It appears that recovery of leached nitrate is only possible in the subhumid zone. In the humid tropics the continuous presence of a deep root system as part of the crop combination on the field is necessary to use nitrogen efficiently, except when acid soil conditions keep all nitrogen in the ammonium form or when an almost ideal synchronization exists of nitrogen supply and demand during the growing season. Some data are discussed on the root distribution of food crops and on the possibilities to establish a “safety-net” under the crops grown in alleys between deep-rooted hedgerow trees.
Tag: alley cropping
Trees for Food Security- 2 Project Overview in Uganda
Soil Organic Carbon and Nitrogen in Agroforestry Systems in Sub-Saharan Africa: A Review
Assessment of natural vegetative contour strips for soil conservation on shallow calcareous soils in the central Philippines: accomplishment report for the period Nov. 2000 – July 2003
While a good understanding exists of the effects of low-cost natural vegetative contour strips (NVS) in deep acidic soil environments, little is known about the benefits and constraints of using NVS under severely degraded calcerous soil condition. Calcerous soils cover about 20% of the total land area of the philippines, and are also wide-spread in other parts of Southeast asia. They therefore, characterize an important environment that millions of upland farmers depend upon for a living in the region. Shallow calcareous soils are particularly common in the Central Phillipines covering more than half of the total land area of the Visayan islands. Under shallow soil conditions, the effects of soil scouring can be severe because the entire soil may be removed down to the parent rock material.
Contour grass strips and tillage affect corn production on Philippine steepland oxisols
Cultivated steeplands in the humid tropics require better soil management systems to meet increasing food demands. The objective of this 4-yr study was to evaluate the following four contour soil management systems for corn (Zea mays L.) production: (i) contour moldboard plowing (CP); (ii) ridge tillage (RT); (iii) natural grass barrier strips plus moldboard plowing (GCP); and (iv) grass strips plus ridge tillage (GRT). Eight successive corn crops were grown in limed and fertilized soil from 1992 through 1995. On a total land area basis (cropped area plus the area occupied by the grass strips), the 1995 mean grain yields for RT (10.8 Mg ha1) and GRT (10.3 Mg ha1) were significantly greater than yields for CP (10.0 Mg ha1) and GCP (9.6 Mg ha1). The corn grain yields for the CP and RT systems before 1995 ranged from 1.3 Mg ha1 in 1992 to 8.4 Mg ha1 in 1993, while comparable GCP and GRT yields ranged from 1.4 to 7.6 Mg ha1 Excluding the area occupied by the grass strips, the GRT system had the highest 4-yr average corn yield (7.3 Mg ha1) followed by the GCP (7.2 Mg ha1), RT (6.9 Mg ha1) and CP (6.7 Mg ha1) systems. Yields improved during the 1994 and 1995 growing seasons when the grass was not permitted to grow as tall. The combination of contour ridge tillage and contour grass strips has potential for sustaining crop productivity on highly erodible steepland soils in the humid tropics.
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.
A tree/crop interface design and its use for evaluating the potential of hedgerow intercropping
The paper describes a tree/crop interface (TCI) experiment designed to investigate the effects of row orientation using Leucaena leucocephala Lam. Each TCI plot consisted of a regularly pruned Leucaena hedge in the middle and 12 crop rows on either side. Eight such plots were arranged at 45° around a sole Leucaena plot with rows oriented in four compass directions viz., North-South, East-West, Northeast-Southwest and Northwest-Southeast. Results of four years from 1984 to 1987 did not show any effect of row orientation, and similarly, no effect was seen on crop rows due to their location on the windward or leeward side of the hedge. The TCI effect was positive on the first crop row in the first year because Leucaena grew slowly, but depressed the yield of the first 4 to 6 crop rows(1.8 to 2.7 m from hedge) in subsequent years. The negative effect of Leucaena was noted more on sunflower in a relatively dry year than on sorghum in other years. Results from the TCI plots were used to estimate the yield of five hedgerow intercropping (HI) systems with varying alley widths (2.7 to 9.9 m). Comparison with sole stands of Leucaena and crops indicated that HI was more productive particularly at close alley widths. For example, hedges spaced at 2.7 m and 3.6 m averaged 37% and 25% higher productivity than the respective sole stands; but this advantage may be an overestimation of the real potential. The relevance of TCI experiments for studying agroforestry systems, their merits and limitations, especially of the design employed in this study are discussed.
Nutrient harvesting-the tree-root safety net
The hypothesis that deep rooting trees intercept nutrients which have leached below the crop rooting zone and compete for nutrients less strongly than trees rooting mainly within the crop root zone was tested in a mixed alley-cropping system on an Ultisol in North Lampung, Sumatra by measuring uptake of 15N placed at varying soildepths. Gliricidia sepillm, with its predominantly shallow root system, competed strongly for N with the crop and took up little 15N from lower soil depths. In contrast Peltophorum dasyrrachis roots exhibited a higher nutrient uptake activity at lower soildepth thus providing an active ‘safety-net’. Root activity as well as root length density has to be taken into account when assessing the efficiency of the safety-net.i’rellnlnary modelling results using WaNuLCAS suggested that Peltophonlln roots inthe 40-60 cm soil layer could reduce leaching by 5-10% over the course of a maize crop cycle in the rainy season.
Rapid soil redistribution within alleys: why simple extension models for contour hedgerows may not be appropriate
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.