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1.
Indigenous and exotic leguminous shrubs that are promising for planted fallow for soil fertility replenishment in east and southern Africa have been found to harbour many herbivorous insects, giving suspicion that widespread adoption of fallow systems may aggravate insect pests. Studies were conducted on farms in western Kenya from 1999 to 2001 to monitor the abundance of herbivorous insects and assess their effects on biomass yields of pure and mixed fallows. The treatments tested were single and two-species mixtures of Tephrosia vogelii, Sesbania sesban and Crotalaria grahamiana and a natural fallow in a split plot design, with the fallow systems in the main plots and protection vs. no protection against insects in sub-plots spread over six farms. Eighteen insect species belonging to seven orders and 14 families were identified as pests of␣the fallows with varied abundance and infestation level across the sites. While Hilda patruelis and Amphicallia pactolicus were most damaging to C. grahamiana, Mesoplatys ochroptera was detrimental to S.␣sesban. T. vogelii hosted fewer insects than others. Nevertheless the pest infestation did not cause significant biomass yield reduction during the study period. Pest attack was generally greater in villages that had been testing the planted fallows for some years compared with villages that took up the fallows recently. This indicates the potential for increased pest infestation with increased adoption of the system by farmers. Multi-species fallows did not indicate any advantage over single species fallows in terms of either reduced pest incidence or increased biomass production. 相似文献
2.
Striga
hermonthica (striga) weed is a major threat to crop production in sub-Saharan Africa, and short duration improved fallow species have
recently been found to reduce the effects of this weed because of their ability to replenish soil nitrogen. The objective
of this study was to compare the efficacy and profitability of coppicing improved fallow species (Gliricidia sepium [gliricidia], Leucaena trichandra [leucaena] and Calliandra calothyrsus [calliandra]) and non-coppicing species (Sesbania sesban [sesbania], Mucuna pruriens [mucuna], and Tephrosia vogelii [tephrosia]), in controlling striga. Natural fallow and a sole maize crop were included as control treatments. The fallow
treatments were split into two and either fertilized with N or unfertilized. The results showed that coppicing fallows produced
higher biomass than non-coppicing fallows. For example, Callindra (coppicing fallow species) produced 19.5 and 41.4 Mg ha−1 of leafy and woody biomass, respectively after four cumulative harvests as compared with Sesbania (non-coppicing species),
which produced only 2.3 and 5.9 Mg ha−1 leaf and woody biomass, respectively. Improved fallows reduced striga population in proportion to the amount of leafy biomass
incorporated into the soil (r = 0.87). N application increased cumulative maize yield by between 15–28% in improved fallow
systems and by as much as 51–83% in the control treatments. Added total costs of the coppicing fallows did not differ significantly
from those of the non-coppicing fallows and control treatments. However, the added net benefits of the coppicing fallows were
significantly higher (US$ 527 for +N and 428 for −N subplots; P < 0.01) than those of the non-coppicing fallows (US$ 374 for +N and 278 for −N), and the least for the control treatments.
The most profitable fallow system was Tephrosia with net added benefits of US$ 453.5 ha−1 season−1 without N, and US$ 586.7 ha−1 season−1 with added N. 相似文献
3.
The rotation of maize (Zea mays) with fast-growing, N2-fixing trees (improved fallows) can increase soil fertility and crop yields on N-deficient soils. There is little predictive understanding on the magnitude and duration of residual effects of improved fallows on maize yield. Our objectives were to determine the effect of fallow species and duration on biomass production and to relate biomass produced during the fallow to residual effects on maize. The study was conducted on an N-deficient, sandy loam (Alfisol) under unimodal rainfall conditions in Zimbabwe. Three fallow species — Acacia angustissima, pigeonpea (Cajanus cajan), and Sesbania sesban — of one-, two-, and three-year duration were followed by three seasons of maize. Pigeonpea and acacia produced more fallow biomass than sesbania. The regrowth of acacia during post-fallow maize cropping provided an annual input of biomass to maize. Grain yields for the first unfertilized maize crop after the fallows were higher following sesbania (mean = 4.2 Mg ha–1) than acacia (mean = 2.6 Mg ha–1). The increased yield of the first maize crop following sesbania was directly related to leaf biomass of sesbania at the end of the fallow. Nitrogen fertilizer did not increase yield of the first maize crop following one- and two-year sesbania fallows, but it increased yield following acacia fallows. Nitrogen fertilizer supplementation was not required for the first maize crop after sesbania, which produced high-quality biomass. For acacia, which produced low-quality biomass and regrew after cutting, N fertilizer increased yield of the first post-fallow maize crop, but it had little benefit on yield of the third post-fallow maize crop.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
4.
Nitrogen deficiency is widespread in southern Africa, but inorganic fertilizers are often unaffordable for smallholder farmers. Short-duration leguminous fallows are one possible means of soil fertility restoration. We monitored preseason topsoil (0 to 20 cm) ammonium and nitrate, fallow biomass production and grain yields for three years in a relay cropping trial with sesbania [Sesbania sesban (L.) Merr.] and maize (Zea mays L.). Sesbania seedlings were interplanted with maize during maize sowing at 0, 7400 or 14,800 trees ha–1, in factorial combination with inorganic N fertilizer at 0 or 48 kg N ha–1 (half the recommended rate). After maize harvest, fallows were allowed to grow during the seven-month dry season, and were cleared before sowing the next maize crop. Both sesbania fallows and inorganic N fertilizer resulted in significantly greater (P < 0.01 to 0.05) preseason topsoil nitrate-N than following unfertilized sole maize. In plots receiving no fertilizer N, preseason topsoil inorganic N correlated with maize yield over all three seasons (r
2 = 0.62, P < 0.001). Sesbania fallows gave significantly higher maize yields than unfertilized sole maize in two of three years (P < 0.01 to 0.05). Sesbania biomass yields were extremely variable, were not significantly related to sesbania planting density, and were inconsistently related to soil N fractions and maize yields. Short-duration fallows may offer modest yield increases under conditions where longer duration fallows are not possible. This gain must be considered against the loss of pigeonpea (Cajanus cajan L. Millsp) harvest in the similarly structured maize-pigeonpea intercrop common in the region.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
5.
An experiment was carried out in a slash-and-burn production system in northern Laos to evaluate legume establishment methods
and effects of legume species on fallow vegetation, weeds, yield of upland rice, and soil parameters. Cajanus cajan, Calliandra
calothyrsus, Crotalaria anagyroides, Flemingia congesta, Leucaena leucocephala, and Sesbania sesban were dibbled separately
or mixed with rice. Legume and planting method had no effect on rice yield. Legume establishment was slightly improved and
vigor after rice harvest was higher when planted in separate hills. Compared to control (no legume), the above ground fallow
biomass observed 13 months after establishment, consisting mostly of Chromolaena odorata, was reduced by 68% with C. anagyroides
and by 40% with L. leucocephala, while other species had no effect. Most of the C. cajan and S. sesban plants died. In March
1995, 22 months after planting, the biomass was 0.21, 0.25, 1.62 and 2.56 kg m-2 for F. congesta, C. calothyrsus, C. anagyroides, and L. leucocephala, respectively. Legume species had no effect on rice
yield or weed biomass in the rice crop. The species tested can influence fallow vegetation but do not allow for field preparation
without burning. Compared to mulching, burning of residue reduced weed biomass by 42%, soil organic C by 9% and the C/N ratio
by 6% but increased extractable P by 90% and pH by 8%.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
6.
Managed short-duration fallows may have the potential to replace longer fallows in regions where population density no longer
permits slow natural fallow successions. The purpose of fallows is not only to improve subsequent crop performance but also
to restore soil fertility and organic matter content for the long term. We therefore evaluated the soil organic matter and
nutrient flows and fractions in a short fallow experiment managed in the western Kenya highlands, and also compared the experimental
area with a 9–12-yr-oldadjacent natural bush fallow. The factorial agroforestry field experiment with four land-use and two
P fertilizer treatments on a Kandiudalfic Eutrudox showed that 31-wk managed fallows with Tithonia diversifolia(Hemsley) A. Gray and Crotalaria grahamiana Wight &Arn. improved soil fertility and organic matter content above those of a natural weed fallow and continuous maize
(Zea mays L.). Post-fallow maize yields were also improved, although cumulative three-season increases in yield were small (0–1.2 Mg
ha−1) when the yield foregone during the fallow season was accounted for. Improvements in yield and soil quality could be traced
to quantity or quality of biomass recycled by the managed fallows. The non-woody recycled biomass produced by the continuous
maize, weed fallow, and tithonia treatments was near 2Mg ha−1, whereas crotalaria produced three times more recyclable biomass and associated N and P. Increases in topsoil N due to the
fallows may have been attributable in part to deep acquisition and recycling of N by the fallows. Particulate macro-organic
matter produced by the fallows contained sufficient N(30–50 kg ha−1) to contribute substantially to maize production. Organic Paccumulation (29 kg ha−1) similarly may play a significant role in crop nutrition upon subsequent mineralization. The effect of the P fertilizer application
on soil properties and maize yield was constant for all land-use systems (i.e., no land-use system × P fertilizer interactions
occurred). There was an indication that tithonia may have stimulated infestation of Striga hermonthica (Del.) Benth., and care must be taken to evaluate the full effects of managed fallows over several seasons.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
7.
Fuelwood is the main energy source for households in rural Africa, but its supply is rapidly declining especially in the densely
populated areas. Short duration planted tree fallows, an agroforestry technology widely promoted in sub-Sahara Africa for
soil fertility improvement may offer some remedy. Our objective was to determine the fuelwood production potential of 6, 12
and 18 months (the common fallow rotation periods) old Crotalaria grahamiana, Crotalaria paulina, Tephrosia vogelli and Tephrosia candida fallows under farmer-managed conditions in western Kenya. Based on plot-level yields, we estimated the extent to which these
tree fallows would meet household and sub-national fuelwood needs if farmers planted at least 0.25 hectares, the proportion
of land that is typically left under natural fallows by farmers in the region. Fuelwood yield was affected significantly (P < 0.05) by the interaction between species and fallow duration. Among the 6-month-old fallows, T. candida produced the highest fuelwood (8.9 t ha−1), compared with the rest that produced between 5.6 and 6.2 t ha−1. Twelve months old T. candida and C. paulina also produced significantly higher fuelwood yield (average, 9.6 t ha−1) than T. vogelli and C. grahamiana of the same age. Between the fallow durations, the 18-month fallows produced the most fuelwood among the species evaluated,
averaging 14.7 t ha−1. This was 2–3 times higher than the average yields of 6 and 12-month-old fallows whose yields were not significantly different.
The actual fuelwood harvested from the plots that were planted to improved fallows (which ranged from 0.01 to 0.08 ha) would
last a typical household between 11.8 and 124.8 days depending on the species and fallow duration. This would increase to
268.5 (0.7 years) and 1173.7 days (0.7–3.2 years) if farmers were to increase area planted to 0.25 ha. Farmers typically planted
the fallows at high stand densities (over 100,000 plants ha−1 on average) in order to maximize their benefits of improving soil fertility and providing fuelwood at the same time. This
potential could be increased if more land (which fortunately exists) was planted to the fallows within the farms in the region.
The research and development needs for this to happen at the desired scale are highlighted in the paper. 相似文献
8.
在撒哈拉以南的非洲地区,黄独脚金寄生杂草（Strigahermonthica）侵扰是限制小农产自给性农业生产的主要因素之一。土壤肥力低加之总体环境退化是寄生杂草侵扰产生的重要原因。引入改良的耕作制度来解决寄生杂草侵扰和土壤肥力下降的问题势在必行。本文对肯尼亚西部双峰高原地区内,用豆科植物--印度田菁改良的休耕地对玉米产量和农田寄生杂草侵扰的作用进行了研究。实验处理分阶段进行,处理包括田菁改良6和18个月的休耕地、未经耕作自然植物再生6和18个月的休耕地、连续种植玉米未施肥的耕地和连续种植玉米同时施加氮和磷肥的耕地。结果表明,与未施肥玉米地相比,田菁改良休耕地明显（p〈0.5）增加玉米产量.除草管理降低了第一季度（428000±63000株·hm-2）、第二季度（51000±1500株·hm-2）玉米地寄生杂草植株种群。实验周期内,除草管理降低玉米地土壤中寄生杂草种子种群数。短期田菁改良休耕地对玉米产量的促进作用明显好于未施肥的玉米地,但是短期杂草休耕地对玉米产量无显著影响。种植玉米和除草控制寄生杂草效果要好于休耕。 相似文献
9.
Sesbania [Sesbania sesban (L.) Merr.] fallows are being promoted as a means for replenishing soil fertility in N-depleted soils of small-scale, resource-poor
farmers in southern Africa. Knowledge of soil water distribution in the soil profile and water balance under proposed systems
is important for knowing the long-term implications of the systems at plot, field and watershed levels. Soil water balance
was quantified for maize (Zea mays L.) following 2-year sesbania fallow and in continuous maize with and without fertilizer during 1998–1999 and 1999–2000 at
Chipata in eastern Zambia. Sesbania fallow increased grain yield and dry matter production of subsequent maize per unit amount
of water used. Average maize grain yields following sesbania fallow, and in continuous maize with and without fertilizer were
3, 6 and 1 Mg ha−1 with corresponding water use efficiencies of 4.3, 8.8 and 1.7 kg mm−1 ha−1, respectively. Sesbania fallow increased the soil-water storage in the soil profile and drainage below the maximum crop root
zone compared with the conventionally tilled non-fertilized maize. However, sesbania fallow did not significantly affect the
seasonal crop water use, mainly because rainfall during both the years of the study was above the normal seasonal water requirements
of maize (400 to 600 mm). Besides improving grain yields of maize in rotation, sesbania fallows have the potential to recharge
the subsoil water through increased subsurface drainage and increase nitrate leaching below the crop root zone in excess rainfall
seasons.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
10.
Improved fallows have been used to reduce time required for soil fertility regeneration after cropping in low input agricultural
systems. In semi-arid areas of Southern Africa, Acacia angustissima and Sesbania sesban are among some of the more widely used improved fallow species. However the residual effects of improved fallows on soil
hydraulic properties during the cropping phase is not known. The aim of this study was to quantify the residual effects of
fallows and tillage imposed at fallow termination on soil hydraulic properties (infiltration rates, hydraulic conductivity
and soil porosity) during the cropping phase. Treatments evaluated were planted fallows of Acacia angustissima, Sesbania sesban and natural fallow (NF) and continuous maize as a control. Steady state infiltration rates were measured using a double ring
infiltrometer and porosity was calculated as the difference between saturated infiltration rates and tension infiltration
measurements on an initially saturated soil. Unsaturated hydraulic conductivity (Ko) and mean pore sizes of water conducting pores were measured using tension infiltrometer at tensions of 5 and 10 cm of water
on an initially dry soil. While there was no significant difference in steady state infiltration rates from double ring infiltrometer
measurements among the fallow treatments, these were significantly higher than the control. The steady state infiltration
rates were 36, 67, 59 and 68 mm h-1 for continuous maize, A. angustissima, S. sesban and NF respectively. Tillage had no significant effect on steady state infiltration rate. Pore density at 5 cm tension was
significantly higher in the three fallows than in maize and varied from 285–443 m−2 in fallows, while in continuous maize the pore density was less than 256 m−2. At 10 cm tension pore density remained significantly higher in fallows and ranged from 4,521–8,911 m−2 compared to 2,689–3,938 m−2 in continuous maize. Unsaturated hydraulic conductivities at 5 cm tension were significantly higher in fallows than in continuous
maize and were 0.9, 0.7, 0.8 cm and 0.5 cm h−1 for A. angustissima, S. sesban, NF and continuous maize, respectively. However there were no significant treatment differences at 10 cm tension. Fallows
improved infiltration rates, hydraulic conductivity and soil porosity relative to continuous maize cropping. Through fallowing
farmers can improve the soils hydraulic properties and porosity, this is important as it affects soil water recharge, and
availability for plant growth 相似文献
11.
The rotation of leguminous shrubs and crops is being tested on farms and recommended as a means of improving soil fertility and increasing crop yield in eastern and southern Africa, including western Kenya. However, this improved fallow practice may also increase the nematode population in the soil. An experiment was conducted to monitor the effects of plant-parasitic nematodes on crops after improved fallow. Soil was collected from a maize (Zea mays L.)/bean (Phaseolus vulgaris L.) field, a natural fallow, a Crotalaria (Crotalaria grahamiana Wight & Arn.) fallow, a Tephrosia (Tephrosia vogelii Hook. f.) fallow and a Crotalaria — Tephrosia mixed fallow and used to fill plastic pots placed in a shade. Three successive crop cycles of 2 months were tested in these pots using maize and beans, the most important staple foods in western Kenya. In the first cycle, beans grew poorly on the Tephrosia and Crotalaria — Tephrosia soil due to the high incidence of root knot nematodes, Meloidogyne spp., while maize did not suffer any loss. Although the populations of root knot nematodes reduced drastically in the second and third cycles, both maize and beans experienced heavy losses on the soil under improved fallow probably due to the spiral nematodes, Scutellonema spp., which became dominant in the nematode communities. Despite the use of fertilisers (N, P, K), both crops became highly sensitive to spiral nematodes in the third cycle because of the degradation of the soil physical properties. The study showed that the benefits of improved fallows in terms of crop production may be limited by the high number of plant-parasitic nematodes they help develop in the process.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
12.
The widespread planting of Sesbania sesban fallows for replenishing soil fertility in eastern Zambia has the potential of causing pest outbreaks in the future. The
pure S. sesban fallows may not produce enough biomass needed for replenishing soil fertility in degraded soils. Therefore, an experiment
was conducted at Kagoro in Katete district in the Eastern Province of Zambia from 1997 to 2002 to test whether multi-species
fallows, combining non-coppicing with coppicing tree species, are better than mono-species fallows of either species for soil
improvement and increasing subsequent maize yields. Mono-species fallows of S. sesban (non-coppicing), Gliricidia sepium, Leucaena leucocephala and Acacia angustissima (all three coppicing), and mixed fallows of G. sepium + S. sesban, L. leucocephala + S. sesban, A. angustissima + S. sesban and natural fallow were compared over a three-year period. Two maize (Zea mays) crops were grown subsequent to the fallows. The results established that S. sesban is poorly adapted and G. sepiumis superior to other species for degraded soils. At the end of three years, sole G. sepium fallow produced the greatest total biomass of 22.1 Mg ha−1 and added 27 kg ha−1 more N to soil than G. sepium + S. sesban mixture. During the first post-fallow year, the mixed fallow at 3.8 Mg ha−1 produced 77% more coppice biomass than sole G. sepium, whereas in the second year both sole G. sepium and the mixture produced similar amounts of biomass (1.6 to 1.8 Mg ha−1). The G. sepium + S. sesban mixture increased water infiltration rate more than sole G. sepium, but both these systems had similar effects in reducing soil resistance to penetration compared with continuous maize without
fertilizer. Although sole G. sepium produced high biomass, it was G. sepium + S. sesban mixed fallow which resulted in 33% greater maize yield in the first post-fallow maize. However, both these G. sepium-based fallows had similar effects on the second post-fallow maize. Thus the results are not conclusive on the beneficial
effects of G. sepium + S. sesban mixture over sole G. sepium.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
13.
S. M. Gathumbi 《Agroforestry Systems》2004,60(3):233-237
Accurate quantitative assessment of roots is key to understanding the belowground plant productivity as well as providing
an insight of the plant-soil interactions. In this study, root recoveries by sieves of different mesh sizes (2.0, 1.0, 0.5
and 0.25 mm) were measured for five tropical tree and shrub species grown in monoculture stands: crotalaria (Crotalaria grahamiana Wight and Arn.), pigeonpea [Cajanus cajan (L.) Millsp.], sesbania [Sesbania sesban (L.) Merr.], tephrosia (Tephrosia vogelii Hook F.), siratro [Macroptilium atropurpureum (DC.) Urb.] and tithonia [Tithonia diversifolia (Hemsl.) Gray]. Root samples were take from 0-15 cm soil depth. Recovery of coarser roots (>1.0 mm) ranged from 70 to 93%
and 90 to 98% of the cumulative root length and biomass respectively. The proportion of root length of the finer roots (<1.0
mm) was greater for pigeonpea (30%), tithonia (22%) and siratro (18%) compared with other species, but contributed negligibly
to the cumulative total root biomass for all species. The use of 0.5 mm sieve improved the recovery of root length for most
species but had little effect on root biomass. The 0.25 mm sieve was most effective in capturing finer roots (<0.5 mm) of
pigeonpea which represented 16% of cumulative root length and 4% of root biomass recorded for this species. Recovery of roots
of different diameter classes depended on species, suggesting that for an improved estimation of root parameters especially
when sieves of large mesh sizes (>0.25 mm) are used, a correction factor could be useful for root length measurements but
not root biomass measurements for a particular species in each site and for a specific study.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
14.
Striga hermonthica is a major constraint to smallholder subsistence agriculture production in the sub-Saharan African region. Low soil fertility
and overall environmental degradation has contributed to the build-up of the parasitic weed infestation. Improved cropping
systems have to be introduced to address the interrelated problems of S. hermonthica and soil fertility decline. Thus, the effects of improved fallow with leguminous shrub Sesbania sesban on maize yields and levels of S. hermonthica infestation on farm land in the bimodal highlands of western Kenya were investigated. The experimental treatments were arranged
in a phased entry, and randomized complete block scheme were six months Sesbania fallow, 18 months Sesbania fallow, six months natural fallow consisting of regrowth of natural vegetation without cultivation, 18 months natural fallow,
continuous maize cropping without fertilizer application, and continuous maize cropping with P and N fertilization. Results
show that Sesbania fallows significantly (p<0.05) increase maize yield relative to continuous unfertilized maize. S. hermonthica plant populations decrease in continuous maize between the first season (mean = 428 000 ± 63 000 ha−1) and second season (mean=51 000 ± 15 000 ha−1), presumably in response to good weed management. S. hermonthica seed populations in the soil decrease throughout the duration of the experiment in the continuous maize treatments. Short-duration
Sesbania fallows can provide modest yield improvements relative to continuous unfertilized maize, but short-duration weedy fallows
are ineffective. Continuous maize cultivation with good weed control may provide more effective S. hermonthica control than fallowing. 相似文献
15.
Roots of trees (Sesbania sesban) and crops (Zea mays) were quantified during two tree/crop cycles in a sequential tree — crop system at Chipata, Eastern Zambia. The experiment included one- and two-year fallows as well as fertilized and unfertilized controls. The roots of S. sesban represent a standing biomass in the soil of 3 Mg hat-1 in the top 1.5 m after two years, with 45–60% and 70–75% being in the top 25 and 50 cm respectively. S. sesban fallow improved early rooting and growth of the following maize crop. Increased soil infiltration was also observed in the two-year fallow treatment, as well as decreased bulk density and resistance to penetration in the soil. No differences between maize root parameters could be detected at tasselling, nor differences between nutrient status of the different treatments. Study results indicate that under the drought-prone conditions of Eastern Zambia, where improved soil physical conditions are important for early deep rooting of crops and access to water and nutrients, tree roots could play an important role in the fallow effect. Further studies are required to assess the relative importance of the improvement of soil chemical and physical properties.Submitted as ICRAF Journal Article # 95/28. 相似文献
16.
In eastern Zambia, nitrogen deficiency is a major limiting factor for increased food production. Soil fertility has been declining because of nearly continuous maize (Zea mays) cultivation with little or no nutrient inputs. The use of short-duration tree fallows was one of several agroforestry options hypothesized to restore soil fertility. Sesbania sesban, an indigenous N2-fixing tree was the most promising among species tested in screening trials. Several studies since 1987 have demonstrated the dramatic potential of two- or three-year sesbania fallows in restoring soil fertility and increasing maize yields. Analyses showed that these improved fallow systems were feasible, profitable, and acceptable to farmers. Results suggest that high maize yields following fallows are primarily due to improved N input and availability by the fallows. The potential to increase maize production without applying mineral fertilizers has excited thousands of farmers who are enthusiastically participating in the evaluation of this technology. The number of farmers who are testing a range of improved fallow practices has increased from 200 in 1994 to over 3000 in 1997. Presently, a strong network of institutions comprising government, NGOs, development projects, and farmer organizations is facilitating the adaptive research and expansion of improved fallow technology in eastern Zambia. Key elements in the research process that contributed to the achievements are effective diagnosis of farmers' problems, building on farmers' indigenous knowledge, generating several different fallow options for farmers to test, ex-ante economic analysis, farmer participation in on-farm trials, and development of a network for adaptive research and dissemination.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
17.
The sesbania beetle, Mesoplatys ochroptera Stål (Chrysomelidae: Coleoptera), is a serious defoliator of Sesbania sesban in eastern and southern Africa. Developing integrated pest management practices against the beetle is an important aspect of the adoption of S. sesban as an improved fallow species. Field studies were conducted in eastern Zambia with the objective of determining the incidence of M. ochroptera on S. sesban in pure and mixed species fallows. M. ochroptera did not successfully feed or breed on species other than S. sesban either in the pure or mixed species fallows. The density of adult and immature stages of M. ochroptera was higher in mixtures of S. sesban with Mucuna pruriens, Macrotyloma axillare, Macroptilium atropurpureum or Crotalaria grahamiana compared to a pure S. sesban fallow. Although mixed fallows of S. sesban with M. axillare and M. pruriens may produce fodder, increase the amount and quality of organic inputs and improve nutrient cycling in the soil, they appear to be incompatible with management of M. ochroptera. Mixing S. sesban with G. sepium neither increased larval and adult populations of M. ochroptera feeding on S. sesban nor damage to it. While this mixture appeared to favour development of pupae to the adult stage, it increased mortality of emerging adults. Therefore, it is concluded that mixing S. sesban with G. sepium is more robust in nutrient cycling, improving resource utilisation and management of M. ochroptera on S. sesban.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
18.
Three multipurpose tree species (MPTS)-leucaena (Leucaena leucocephala), sesbania (Sesbania sesban var. nubica) and pigeonpea (Cajanus cajan) were pruned at a height of 60 cm above the ground every two months, and resulting plant biomass was incorporated into the soil as green manure. For comparison, maize (Zea mays) stover was also incorporated into some plots, while some other plots were left fallow. Varying quantities of plant biomass which were incorporated into the soil over a period of 12 months caused large changes in major soil plant nutrients, and it substantially improved soil fertility. To test for improved soil fertility, test crops of maize and beans (Phaseolus vulgaris) were grown on the plots after six biomass incorporations of 4806, 13603, 16659 and 7793 kg. ha–1yr–1 for pigeonpea, sesbania leucaena and maize, respectively. Responses of the test crops indicated that sesbania and leucaena green manures improved maize stover, cobs and grain yields; and bean haulms and grain yields by 77.6% when compared to fallow plots. Residual effects of green manures still resulted in significant (P < 0.05) yield differences in the test cropin the third testing season. Economic significance of green manures in increasing food crop yields to small scale farmers is discussed. 相似文献
19.
Trees can influence both the supply and availability of nutrients in the soil. Trees increase the supply of nutrients within
the rooting zone of crops through (1) input of N by biological N2 fixation, (2) retrieval of nutrients from below the rooting zone of crops and (3) reduction in nutrient losses from processes
such as leaching and erosion. Trees can increase the availability of nutrients through increased release of nutrients from
soil organic matter (SOM) and recycled organic residues.
Roots of trees frequently extend beyond the rooting depth of crops. Research on a Kandiudalfic Eutrudox in western Kenya showed
that fast-growing trees with high N demand (Calliandra calothyrsus, Sesbania sesban and Eucalyptus grandis) took up subsoil
nitrate that had accumulated below the rooting depth of annual crops. Sesbania sesban was also more effective than a natural
grass fallow in extracting subsoil water, suggesting less leaching loss of nutrients under S. sesban than under natural uncultivated
fallows.
Nutrient release from SOM is normally more dependent on the portion of the SOM in biologically active fractions than on total
quantity of SOM. Trees can increase inorganic soil N, N mineralization and amount of N in light fraction SOM. Among six tree
fallows of 2- and 3-year duration on an Ustic Rhodustalf in Zambia, inorganic N and N mineralization were higher for the two
tree species with lowest (lignin + polyphenol)-to-N ratio (mean = 11) in leaf litter than for the two tree species with highest
ratio (mean = 20) in leaf litter. Trees can also restore soil fauna, which are important for SOM and plant residue decomposition.
Some agroforestry trees have potential to provide N in quantities sufficient to support moderate crop yields through (i) N
inputs from biological N2 fixation and retrieval of nitrate from deep soil layers and (ii) cycling of N from plant residues and manures. The cycling
of P from organic materials is normally insufficient to meet the P requirements of crops. Sustained crop production with agroforestry
on P-deficient soils will typically require external P inputs.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
20.
Alley cropping with leguminous tree hedgerows planted on contours is an emerging practice in the northern highlands of Rwanda
where field slopes range from 4 to 76% and loss of soil fertility due to erosion is the principal impediment to food production.
Sesbania sesban and Leucaena Leucocephala, the two woody species recommended for alley cropping in the region, do not perform
equally well across sites: Sesbania is faster growing, But is more sensitive to pruning than Leucaena. We tested the hypothesis
that the two species could be grown together to make the best use of their relative advantages. Species were planted in pure
and 1:1 mixed stands at 26 sites to give a range of altitudes, slopes, azimuths and soil fertility levels representative of
the region. During two cropping seasons’ growth spanning 19 months, in pure stands, Sesbania produced more biomass, grew taller
and had thicker stems than Leucaena: for the same species, stem diameter and height were not different in pure and mixed stands.
Biomass and number of poles from 1:1 mixed stands of Sesbania and Leucaena were equivalent to biomass and pole numbers from
Sesbania in pure stands. However, mixed stands produced more biomass and pole numbers than Leucaena in pure stands. Growth
of S. sesban was positively correlated with soil pH, potassium and altitude; whereas, growth of L. leucocephala was positively
correlated with soil phosphorus, but negatively correlated with field slope. All other soil and site variables tested were
nonsignificant. The study suggests that farmers can plant S. sesban and L. leucocephala in 1:1 mixtures in an alley cropping
setting and retain levels of biomass production and bean pole numbers equivalent to those from S. sesban alone without compromising
future growth and production by Leucaena. As well, the impact of pH, K and P on growth and production of Sesbania and Leucaena
as a function of field slope and altitude should be determined before extending their use to other regions.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献