Biophysical interactions in tropical agroforestry systems

sequential systems, simultaneous systems Abstract. The rate and extent to which biophysical resources are captured and utilized by the components of an agroforestry system are determined by the nature and intensity of interac-tions between the components. The net effect of these interactions is often determined by the influence of the tree component on the other component(s) and/or on the overall system, and is expressed in terms of such quantifiable responses as soil fertility changes, microclimate modification, resource (water, nutrients, and light) availability and utilization, pest and disease incidence, and allelopathy. The paper reviews such manifestations of biophysical interactions in major simultaneous (e.g., hedgerow intercropping and trees on croplands) and sequential (e.g., planted tree fallows) agroforestry systems. In hedgerow intercropping (HI), the hedge/crop interactions are dominated by soil fertility improvement and competition for growth resources. Higher crop yields in HI than in sole cropping are noted mostly in inherently fertile soils in humid and subhumid tropics, and are caused by large fertility improvement relative to the effects of competition. But, yield increases are rare in semiarid tropics and infertile acid soils because fertility improvement does not offse

The role of agroforestry trees in intercepting leached nitrogen in the agricultural systems of the Central Highlands of Kenya

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Effects of organic and mineral fertilizer inputs on maize yield and soil chemical properties in a maize cropping systems in Meru South District, Kenya

Soil nutrient depletion as a result of continuous cultivation of soils without adequate addition of external inputs is a major challenge in the highlands of Kenya. An experiment was set up in Meru South District, Kenya in 2000 to investigate the effects of different soil-incorporated organic (manure, Tithonia diversifolia, Calliandra calothyrsus, Leucaena leucocephala) and mineral fertilizer inputs on maize yield, and soil chemical properties over seven seasons. On average, tithonia treatments (with or without half recommended rate of mineral fertilizer) gave the highest grain yield (5.5 and 5.4 Mg ha?1 respectively) while the control treatment gave the lowest yield (1.5 Mg ha?1). After 2 years of trial implementation, total soil carbon and nitrogen contents were improved with the application of organic residues, and manure in particular improved soil calcium content. Results of the economic analysis indicated that on average across the seven seasons, tithonia with half recommended rate of mineral fertilizer treatment recorded the highest net benefit (USD 787 ha?1) while the control recorded the lowest (USD 272 ha?1). However, returns to labor or benefit-cost ratios were in most cases not significantly improved when organic materials were used

Nitrogen fertilizer equivalencies of organics of differing quality and optimum combination with organic nitrogen source in Central Kenya

Decline in crop yields is a major problem facing smallholder farmers in Kenya and the entire Sub-Saharan region. This is attributed mainly to the mining of major nutrients due to continuous cropping without addition of adequate external nutrients. In most cases inorganic fertilizers are expensive, hence unaffordable to most smallholder farmers. Although organic nutrient sources are available, information about their potential use is scanty. A field experiment was set up in the sub-humid highlands of Kenya to establish the chemical fertilizer equivalency values of different organic materials based on their quality. The experiment consisted of maize plots to which freshly collected leaves of Tithonia diversifolia (tithonia), Senna spectabilis (senna) and Calliandra calothyrsus (calliandra) (all with %N>3) obtained from hedgerows grown ex situ (biomass transfer) and urea (inorganic nitrogen source) were applied. Results obtained for the cumulative above ground biomass yield for three seasons indicated that a combination of both organic and inorganic nutrient source gave higher maize biomass yield than when each was applied separately. Above ground biomass yield production in maize (t ha?1) from organic and inorganic fertilization was in the order of senna+urea (31.2), tithonia+urea (29.4), calliandra+urea (29.3), tithonia (28.6), senna (27.9), urea (27.4), calliandra (25.9), and control (22.5) for three cumulative seasons. On average, the three organic materials (calliandra, senna and tithonia) gave fertilizer equivalency values for the nitrogen contained in them of 50, 87 and 118%, respectively. It is therefore recommended that tithonia biomass be used in place of mineral fertilizer as a source of nitrogen. The high equivalency values can be attributed to the synergetic effects of nutrient supply, and improved moisture and soil physical conditions of the mulch. However, for sustainable agricultural production, combination with mineral fertilizer would be the best option

Minimum tillage, tied ridging and mulching for better maize yield and yield stability in the Central Highlands of Kenya

© 2017 Elsevier B.V. Most smallholder farmers in Sub-Saharan Africa and in Kenya have been experiencing a decrease in crop yields in the recent decades. Droughts and prolonged dry spells are common and water is becoming the main limiting factor during crop growing seasons threatening smallholder farmers’ livelihood. Hence, availability and adoption of conservation-effective management practices (CEM) that foster soil conservation, water retention, improved crop yield and yield stability under the small-holder rainfed farming system is desirable. Based on this, we evaluated effects of selected CEM techniques on maize (Zea mays L.) yields, yield stability and farmers’ willingness to take up the techniques. We hypothesized that, the CEM techniques will not only increase maize yield but also the yield stability. The selected CEM were minimum tillage (MT), mulching (MC) and tied ridging (TR) tested alongside a control (conventional tillage) (CT) in two sites, a semi-arid (with predominant soil type being Cambisols with cambic B horizons) and sub-humid agro-ecologies (with predominant soil type being Humic Nitisols), in the Central Highlands of Kenya. We implemented field trials on-farm for four seasons: short rains 2011 (SR11), long rains 2012 (LR12), short rains 2012 (SR12) and long rains 2013 (LR13). The test crop was Maize (Zea Mays L.). A key informant's interview with the farmers who implemented the field trial was conducted to assess their willingness to take up CEM techniques. Rainfall distribution and amount varied widely between the two sites. Maize grain yields were significantly higher in TR and MC treatments during the LR12, SR12 and LR13 seasons in the semi-arid site compared to CT. Tied ridging doubled grain yields during SR12 season in the semi-arid site. In the sub-humid site, grain yields significantly increased under all the tested CEM techniques during SR11, LR12 and SR12 seasons. Maize grain yields were more stable under TR and MC with residual variances of 0.107 and 0.183 Mg ha−2, respectively in the semi-arid site. Mulching, MT and TR techniques indicated yield stability with residual variances of 0.017, 0.039 and 0.155 Mg ha−2, respectively, in the sub-humid site. We concluded that, under semi-arid conditions, tied ridging is a better CEM technique that not only positively affect maize yields but it also enhances yield stability. Under sub-humid agro-ecological conditions, mulching technique performed comparatively well in terms of increasing maize grain yields and yield stability. The n were further affirmed by the farmers’ willingness to continue practicing TR and MC practice in Mbeere South and Meru South, respectively.status: publishe

Effects of selected soil and water conservation techniques on runoff, sediment yield and maize productivity under sub-humid and semi-arid conditions in Kenya

The aim of this work is to investigate the consequences of selected soil and water conservation techniques and tillage practices on runoff amounts, sediment yield and maize yields under semi-arid and sub-humid environments. Field trials were set in Kigogo primary school in Meru South Sub-County, Tharaka Nithi County, representing the sub-humid conditions, and Machang'a secondary in Mbeere South Sub-County, Embu County (semi-arid) in the central highlands of Kenya. The experiment layout was a randomized complete block design and the treatments were implemented in runoff plots. Tied ridging (TR) was the most efficient technique in reducing runoff and sediment yield and at the same time boosting crop yields in the semi-arid region. It significantly (p<. 0.05) reduced sediment yields by 94% compared to the conventional tillage (CT) during the study period. The effects were particularly strong in periods of below average rainfall (dry seasons). During the drier season of short rains 2010 (SR10), grain yield under TR was 7 times higher compared to CT (p<. 0.01). In the sub-humid region, minimum tillage (MT) generated high runoff but relatively low sediment yield compared to CT. During periods of enough rainfall (over 450. mm per season) in the drier site, intercropping suppressed maize yields significantly (p<. 0.01) by 42% compared to conventional tillage in the drier site. The results on the magnitude of runoff and sediment under the different soil and farm management practices are crucial in selection and promotion of valid farm management practices and tillage alternatives that not only abate soil erosion but also boost agricultural productivity in both sub-humid and semi-arid agro-ecological zones. © 2014 Elsevier B.V.status: publishe