摘要:

Animal manure is used in smallholder farms to improve soil fertility but the quality is often poor. The quality of the manure in the inherent nutrient levels is low and mostly associated with diets fed to the animals and the management of the manure. A study was carried out to investigate carbon and nitrogen (N) mineralisation of cattle manure processed under different management systems. Manure was produced in smallholder farms and in a research station. A detailed laboratory analysis was done to characterise the manure. The manure was subsequently incubated with a humic Nitisol, the dominant soil group in central highlands of Kenya. In the incubation study, data were collected on carbon dioxide evolution and nitrogen mineralisation (NO-3and NH4+). An on-farm trial was conducted to test the effect of two types of manure with different N release rates on maize yield. The on-station manure and manure from farmers' fields showed a net nitrogen release up to 12 weeks of incubation. Some manure from farms immobilised N for most of the incubation period. Carbon dioxide evolution at weeks two and four indicated that there was microbial activity in most of the manure. The release of N in the incubated manure was confirmed in the field study where the on-station manure showed a yield response in maize during the first season. This study shows that manure management affects the rate of N release can affect crop growth in the field. Level of soluble carbon correlated most with N mineralisation.

ISSN:0012-8325    

DOI:10.4314/eaafj.v65i1.1752

出版商:Taylor & Francis    

年代:1999

数据来源: Taylor

摘要:

The effect of irrigation, nitrogen fertiliser and planting density on green leaf area index under field conditions was determined. Field experiments were carried out at Sonning (UK) in summer 1992, and two experiments at Kabete, Kenya from November 1992 to February 1993 (K1) and from February to May 1993 (K2) using beans (Phaseolus vulgarisvar. Mwezi Moja). The treatments included two irrigation levels (not irrigated and irrigated), two fertiliser levels (no fertiliser and 100 kg N ha−1) and two planting densities (22 and 44 m−2) arranged in a split-split plot design. Irrigation was done using a drip system at Sonning and watering cans at K1 and K2. Changes in individual leaf length of the first four middle trifoliate leaflets, the number of leaves per plant and the number of branches per plant were monitored. Leaf area index was largest at Sonning and least at K2. Although irrigation did not have a significant effect on LAI in the three experiments, it was important in maintaining leaf area late in the season at Sonning. Nitrogen increased LAI at Sonning and at K1 when water was not limiting. Nitrogen effect on LAI depended on the growth stage of the crop and total seasonal rainfall. Nitrogen effect on LAI was through increased leaf emergence and extension rate. High planting density increased LAI if water and N supply were not limiting. Leaves at Sonning were thin and wide (photoperiod effect) but small and thickest at Kabete in the dry season (water stress effect). Effective irrigation (above atmospheric evaporation demand), N application and judicious planting density increased LAI.

ISSN:0012-8325    

DOI:10.4314/eaafj.v65i1.1753

出版商:Taylor & Francis    

年代:1999

数据来源: Taylor

摘要:

Beans (Phaseolus vulgarisvar Mwezi Moja) were grown in the field under two irrigation levels (irrigated and rainfed), two nitrogen levels (no fertiliser and 100 kg N ha−1) and two planting densities (22 and 44 plants m−2) at Sonning (UK) and Kabete (Kenya). The crop duration in the three experiments was 114 days in Sonning, 95 days in K1 and 73 days in K2. Irrigation increased total dry matter early in the season at Sonning but had no effect at Kabete experiments because of high rainfall in K1 and ‘ineffective’ irrigation in the drier K2 where most of the water was lost through evaporation.

ISSN:0012-8325    

DOI:10.4314/eaafj.v65i1.1754

出版商:Taylor & Francis    

年代:1999

数据来源: Taylor

摘要:

In the highlands of western Kenya, poor crop growth due to severe nutrient depletion over the past two to three decades has exacerbated soil erosion. The potential benefits of phosphorus (P) recapitalisation with a large one-time application of 500 kg P ha−1and agroforestry in terms of soil, water and nutrient conservation were investigated on P-deficient soils in western Kenya for 3.5-years. The agroforestry systems compared were one-season sesbania (Sesbania sesban) fallow followed by annual crops, and contour hedgerows of calliandra (Calliandra calothyrsus) plus Napier grass (Pennisetum purpureum). Continuous cropping without P fertiliser produced an average runoff of 367 mm (37% of rainfall) and soil displacement of 105 t ha−1per season, with a loss of 159 kg of total N and 46 kg of total P ha−1. Phosphorus application reduced runoff by 31% and soil loss by 59% compared to non-fertiliser applied cropping. In P-replenished soils, neither one-season sesbania fallow nor contour hedgerows affected water runoff but one-season sesbania fallow reduced soil loss by 5% and contour hedgerows reduce soil loss by 20%, over P alone. Nutrient losses due to erosion occurred mainly through sediment movement, and losses through water runoff were negligible. Sesbania fallow and contour hedgerows prevented surface nutrient losses proportionate to their effects on reducing soil erosion. Integrating P and short-duration sesbania fallows in P-deficient soils increases crop yields and can also contribute to soil, water and nutrient conservation by providing a rapid and prolonged ground cover with good crop growth and increased water infiltration into soil. The hedgerows have the added advantage of yielding fodder besides effectively reducing soil and nutrient losses.

ISSN:0012-8325    

DOI:10.4314/eaafj.v65i1.1755

出版商:Taylor & Francis    

年代:1999

数据来源: Taylor

摘要:

An experiment was carried out at Kiomo Agroecological zone 5 to compare the water use efficiency (WUE) and economic benefits of using spot, modified drip (bucket) and furrow irrigation methods. Each of these application techniques was combined with 0, 10 t ha−1of manure and DAP at 200 kg of ha−1. The use of manure combined with fertiliser produced higher quantities of fresh tomatoes, improved WUE and had higher economic benefits. The modified drip and spot irrigation with fertiliser did not differ significantly but produced higher amounts of fresh tomatoes than furrow irrigation. The WUE of spot was superior to that of the other techniques in treatments that received a combination of manure and fertiliser. Without fertiliser the modified drip had higher WUE than the rest. Applying water in spots with fertiliser and its combination with manure had the highest income followed by similar treatments using the modified drip technique. The modified drip was the most efficient in the use of labour and had higher returns in treatments with fertiliser combined with manure.

ISSN:0012-8325    

DOI:10.4314/eaafj.v65i1.1756

出版商:Taylor & Francis    

年代:1999

数据来源: Taylor

摘要:

Average actual cereal yields are a result of both inter-seasonal droughts and intraseasonal dry spells that occur during the cropping season. During dry spells crops cannot effectively use available soil nutrients. In order to decrease the gap between actual and potential cereal yields there is need to minimise the intra-seasonal dry spells. Analyses of water balances for cereal production in the semi-arid areas show that much water is inaccessible to the crop due to poor rainfall distribution. A step towards intra-seasonal dry spell mitigation, the results of rainfall analyses of Machakos District, Kenya are presented in this paper. Rainfall amounts, frequencies and runoff are examined. The main objective is to identify occurrence of intraseasonal dry spells that lower yields on farms. The paper also discusses when these dry spells could have been alleviated through supplemental irrigation of the crop, using a small-scale water harvesting system.

ISSN:0012-8325    

DOI:10.4314/eaafj.v65i1.1757

出版商:Taylor & Francis    

年代:1999

数据来源: Taylor

摘要:

This study aimed at characterising the river flow regime using statistical and probability methods. Streamflow data for Archers Post river gauging station for the period 1960 to 1998 were used for the analysis. Preliminary analysis of the daily flow data was undertaken to determine monthly mean flow, annual mean flow, 7, 30, 90 and 120 days mean low flow and highest daily discharge (flood flow) for each year. Descriptive statistical parameters including: the mean, standard error, median, standard deviation, coefficient of variation, kurtosis, skewness and confidence level of mean at 95% were computed. The cumulative distribution function of the monthly flow showed that February had the lowest flow and November had the highest. Monthly flow analysis revealed that there were three peaks in April, August and November corresponding to the long, continental and short rainy seasons.

ISSN:0012-8325    

DOI:10.4314/eaafj.v65i1.1758

出版商:Taylor & Francis    

年代:1999

数据来源: Taylor

摘要:

The study was conducted on a humic Nitisol at Kabete Field Station, College of Agriculture and Veterinary Sciences, University of Nairobi, Kenya to assess the effect of seven different grass strips on terrace development and maize yield. After nine years of establishment, donkey grass (Panicum trichocladum) was the best in bench development with 6.2% mean slope followed by creeping signal (Brachira humidicola) (5.1%). Bana (Pennisetum purpureum) (4.7%), tall signal (Bracharia ruziziensis), and Guatemala (4.2%), tall guinea (Panicum maximum) (4.0%) and lastly Makarikari (Panicum coloratum var. Makarikarienses) grass (1.8%). Bana and tall guinea grasses significantly (P = 0.001) decreased maize plant heights and yields on the lower and upper terrace positions due to their competitive effects. Maize grain yield was 1.2 t ha−1in the lower terrace position, 2.4 t ha−1in the middle and 1.4 t ha−1in the upper terrace position of bana. Tall guinea terrace maize grain yields were 0.9 t ha−1in the lower position, 2 t ha−1in the middle and 1 t ha−1in the upper position. Yield differences among positions for Makarikari, creeping signal, Donkey and Guatemala grasses were not significant. Of the grasses evaluated, bana and tall guinea would be more appropriate for farmers who are confronted by conservation needs and require fodder for animals.

ISSN:0012-8325    

DOI:10.4314/eaafj.v65i1.1759

出版商:Taylor & Francis    

年代:1999

数据来源: Taylor

摘要:

The construction and continuous cultivation of bench terraces in the densely populated Kigezi highlands of Uganda have concentrated the topsoil on the lower side of the terraces leaving an exposed subsoil in the upper part of the terraces. This leads to a strong yield gradient with negligible production on the upper terrace sections. Unlike crops, agroforestry trees grow well when planted as rotational woodlots on the scoured terrace sections. In on-farm experiments these woodlots produces more than 7 tons ha−1of wood and 8 ton ha−1of green matter. Even after five rotational cycles the survival rates of trees is very good. The woodlots double infiltration rates on the most erodible part of the terrace and rehabilitate soil fertility. If this practice is adopted by many farmers, wood production would increase from 24.5 to 31.5 t ha−1. Crop production would also increase from 1.27 to 4.63 t ha−1, the run-off and erosion will be reduced and terrace stability enhanced.

ISSN:0012-8325    

DOI:10.4314/eaafj.v65i1.1760

出版商:Taylor & Francis    

年代:1999

数据来源: Taylor

摘要:

This study evaluated different soil conservation measures (level and graded bunds, level and graded fanya juu and grass strips in soil conservation, soil nutrient retention and crop yields) in the Harerge highlands of Ethiopia. The soil conservation measures showed varied performance in controlling soil loss, retention of different soil properties and crop yields. Level bund and level fanya juu were significantly (P = 0.05) different from the control in controlling runoff and soil loss. The grass strips were intermediate between the level and graded structures in controlling soil loss. There was a general increase in both organic carbon (OC) and total nitrogen (TN) percentage after the establishment of the soil conservation measures. An average increase of 0.28% in OC and 0.16% in TN was observed in 1997, as compared to the initial soil nutrient content determined before the establishment of the trials in 1983. Grain yield was increased by 12.3%, on level bund, 4.2% on level fanya juu, 14.9% on graded bund and 6.5% on graded fanya juu as compared to the control plots. However, the yields were 4.35% less from the grass strips than from the control. The level bund showed relatively better overall performance than other techniques tested in the area in terms of erosion control, nutrient retention and crop yields.

ISSN:0012-8325    

DOI:10.4314/eaafj.v65i1.1761

出版商:Taylor & Francis    

年代:1999

数据来源: Taylor