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1.
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
2.
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
3.
Research on improved fallows has concentrated on soil fertility benefits neglecting possible benefits to soil and water conservation.
The effects of improved fallows on rainfall partitioning and associated soil loss were investigated using simulated rainfall
on a kaolinitic soil in Zimbabwe. Simulated rainfall at an intensity of 35 mm h−1 was applied onto plots that were under planted fallows of Acacia angustissima and Sesbania sesban, natural fallow and maize (Zea mays L.) for two years. At the end of 2-years in October 2000, steady state infiltration rates could not be determined in A. angustissima and natural fallow plots, but they were 24 mm h−1 in S. sesban and 5 mm h−1 in continuous maize. The estimated runoff losses after 30 min of rainfall were 44% from continuous maize compared with 22%
from S. sesban and none from A. angustissima and natural fallow plots. Infiltration rate decay coefficients were 36 mm and 10 mm for S. sesban and continuous maize, respectively. In October 2001 after one post-fallow crop, it was still not possible to determine the
steady state infiltration rates in A. angustissima and natural fallows, but they were 8 and 5 mm h−1 for, S. sesban and continuous maize systems, respectively. The runoff loss, averaged across tilled and no-tilled plots, increased to 30%
in the case of S. sesban fallowed plots and 57% for continuous maize; there was still no runoff loss from the other treatments. There were significant
differences (P<0.05) in infiltration rate decay coefficients among treatments. The infiltration rate decay coefficient was 25 mm for S. sesban and it remained unchanged at 10 mm for continuous maize. It is concluded that planted tree fallows increase steady state
infiltration rates and reduce runoff rates, but these effects markedly decrease after the first year of maize cropping in
non-coppicing tree fallows.
This revised version was published online in June 2006 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.
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
6.
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
7.
Fallowing can improve crop yields as a result of improved soil fertility and nutrient status. The objective of this work was
to determine the effects of fallows and pruning regimes in coppicing fallows on soil moisture and maize yields under conventional
tillage (CT) and no tillage (NT). Fallows that were evaluated were coppicing Acacia angustissima, non coppicing Sesbania sesban, natural fallow (NF) and continuous maize. In 2000/2001 season, maize yields were significantly different (P < 0.05) among treatments and were; 1.8, 1.2, 0.7 and 0.5 tonnes per hectare (t ha−1) under CT, while under NT yields were 1.3, 0.8, 0.7 and 0.2 t ha−1 for A. angustissima, maize, S. sesban and NF plots respectively. In 2001/2002 season, yields decreased in the order S. sesban > continuous maize > NF > A. angustissima, for both CT and NT. The 2-week pruning regime had significantly higher maize yields when compared to the 1 and 3 week pruning
regime during the 2002/2003 cropping season. For the three seasons, CT had significantly higher yields than NT. A. angustissima had significantly higher mean available water at suctions <33 kPa for the 0–25 cm depth when compared to other fallow treatments.
The bulk of the available water (47–80%) was retained at suction <33 kPa for all treatments and depths. There were no treatment
differences in water retention at suctions >33 kPa for all treatments. It was concluded that improved fallowing increased
yields when compared to NF. However, in coppicing fallows competition for water can result in reduced yields when there is
rainfall deficiency, thus the need for pruning to manage the competition. 相似文献
8.
R. Chikowo P. Mapfumo P. Nyamugafata G. Nyamadzawo K.E. Giller 《Agroforestry Systems》2003,59(3):187-195
Improved or planted fallows using fast-growing leguminous trees are capable of accumulating large amounts of N through biological
N2-fixation and subsoil N capture. During the fallow phase, the cycling of nutrients is largely efficient. However, there are
few estimates of the fate of added N during the cropping phase, after the 'safety net' of fallow-tree roots is removed. Nitrate-N
at the end of the fallow phase, which is pre-season to the subsequent crop, was monitored in seven land use systems in successive
20-cm soil layers to 120 cm depth at Domboshawa, Zimbabwe in October 2000. Thereafter, nitrate-N dynamics was monitored during
cropping phase until April 2001 at 2-week intervals in plots that had previously 2-year planted fallows of Acacia angustissima and Sesbania sesban, and in a continuous maize control. Pre-season nitrate concentrations below 60 cm soil depth were <3 kg N ha−1 layer−1 for S. sesban,
A. angustissima, Cajanus cajan and natural woodland compared with the maize (Zea mays L.) control, which had >10 kg N ha−1 layer−1. There was a flush of nitrate in the S. sesbania and A. angustissima plots with the first rains. Topsoil nitrate had increased to >29 kg N ha−1 by the time of establishing the maize crop. This increase in nitrate in the topsoil was not sustained as concentrations decreased
rapidly due to leaching. Nitrate then accumulated below 40 cm, early in the season when maize root length density was still
low (<0.1 cm cm−3) and inadequate to effectively intercept the nitrate. It is concluded that under light soil and high rainfall conditions,
there is an inherent problem in managing nitrate originating from mineralization of organic materials as it accumulates at
the beginning of the season, well ahead of peak demand by crops, and is susceptible to leaching before the crop root system
develops.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
9.
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
10.
Crop and livestock production in the Guinea savanna zone of northern Ghana has been declining over the past years as a result
of increasing pressure on land. To sustain soil productivity, pigeon pea(Cajanus cajan), a leguminous perennial crop was evaluated for its potential as a short duration fallow crop for fodder and grain, and maize
(Zea mays)production. It involved comparing a natural fallow (i.e., control) and four improved fallows of pigeon pea pruned annually
at 30 cm, 60 cm and 90 cm from the ground, and unpruned pigeon pea over a two-year period. After this time, the land was cleared
manually and planted to maize. The highest mean annual biomass of pigeon pea over the two-year period of 6.1 t ha−1 dry matter (DM) was obtained by pruning at 60 cm. The highest leaf litter production and pigeon pea seed yield was obtained
from the no pruning treatment. The mean maize grain yield from the improved fallow (3.02 t ha−1) in the first year after clearing was significantly (P < 0.05) greater than that of the natural fallow (1.54 t ha−1). Considering the biomass of pigeon pea from pruning, pigeon pea seed yield and maize grain yield after the pigeon pea, pruning
pigeon pea at 60 cm is the most promising regime for crop-livestock production systems.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
11.
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
12.
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
13.
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
14.
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
15.
Nitrogen is normally the nutrient most limiting production of maize (Zea mays) — the main staple food crop — in southern Africa. We conducted a field study to determine the effect of N sources on soil nitrate dynamics at three landscape positions in farmers' fields in southern Malawi. The landscape positions were dambo valley or bottomland, dambo margin, and steep slopes. The N sources were calcium ammonium nitrate fertilizer applied at 120 kg N ha–1, biomass from Sesbania sesban, and no added N. Sesbania biomass was produced in situ in the previous season from sesbania relay cropped with maize. Nitrate in the topsoil (0 to 15 cm depth) increased to 85 days after maize planting (mean = 48 kg N ha–1) and then decreased markedly. Application of N fertilizer and sesbania biomass increased soil nitrate, and nitrate-N in topsoil correlated positively with amount of incorporated sesbania biomass. The strongest correlation between sesbania biomass added before maize planting and topsoil nitrate was observed at 85 days after maize planting. This suggests that the sesbania biomass (mean N content = 2.3%) mineralized slowly. Inorganic N accumulated in the subsoil at the end of the maize cropping season when N fertilizer and sesbania were applied. This study demonstrated the challenges associated with moderate quality organic N sources produced in smallholder farmer's fields. Soil nitrate levels indicated that N was released by sesbania residues in the first year of incorporation, but relay cropping of sesbania with maize may need to be supplemented with appropriately timed application of N fertilizer.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
16.
G.I. Nyadzi R.M. Otsyina F.M. Banzi S.S. Bakengesa B.M. Gama L. Mbwambo D. Asenga 《Agroforestry Systems》2003,59(3):253-263
Growing of trees as woodlots on farms for five to seven years in rotation with crops was considered as a potential technology
to overcome the shortage of wood, which is a common problem to many parts of sub-Saharan Africa. The paper summarizes the
results of trials conducted at Tabora and Shinyanga in northwestern Tanzania on rotational woodlots, to evaluate tree species
for wood production and yields of maize grown in association with and after harvest of trees. On acid sandy soils at Tabora,
Acacia crassicarpa A. Cunn. ex Benth. grew fast and produced 24 to 77 Mg ha−1 of wood in four to five years. On alkaline Vertisols at Shinyanga, seven years old woodlots of Acacia polyacantha Willd. and Leucaena leucocephala (Lam.) De Wit. produced 71 and 89 Mg ha−1 of wood, respectively. Intercropping of maize between trees was possible for two years without sacrificing its yield. The
first maize crop following A. crassicarpa woodlots gave 29 to 113% greater yield than the crop after natural fallow. Acacia polyacantha and L. leucocephala woodlots also increased the subsequent maize yields over a three-year period. The increase in crop yields after woodlots
was attributed partly to accumulation of greater amounts of inorganic N in the topsoil compared to the traditional fallow,
and partly to other effects. Thus medium-term rotational woodlots are likely to contribute to meet the wood requirements of
rural people and thereby help protect the natural woodlands in sub-Saharan Africa.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
17.
Land management practices that simultaneously improve soil properties are crucial to high crop production and minimize detrimental
impact on the environment. We examined the effects of crop residues on crop performance, the fluxes of soil N2O and CO2 under wheat-maize (WM) and/or faba bean-maize (FM) rotations in Amorpha fruticosa (A) and Vetiveria zizanioides (V) intercropping systems on a loamy clay soil, in subtropical China. Crop performance, soil N2O and CO2 as well as some potential factors such as soil water content, soil carbon, soil nitrogen, microbial biomass and N mineralization
were recorded during 2006 maize crop cultivation. Soil N2O and CO2 fluxes are determined using a closed-based chamber. Maize yield was greater after faba bean than after wheat may be due to
differences in supply of N from residues. The presence of hedgerow significantly improved maize grain yields. N2O emissions from soils with maize were considerably greater after faba bean (345 g N2O–N ha−1) than after wheat (289 g N2O–N ha−1). However, the cumulated N2O emissions did not differ significantly between WM and FM. The difference in N2O emissions between WM and FM was mostly due to the amounts of crop residues. Hedgerow alley cropping tended to emit more
N2O than WM and FM, in particular A. fruticosa intercropping systems. Over the entire 118 days of measurement, the N2O fluxes represented 534 g N2O–N ha−1 (AWM) and 512 g N2O–N ha−1 (AFM) under A. fruticosa species, 403 g N2O–N ha−1 (VWM) and 423 g N2O–N ha−1 (VFM) under Vetiver grass. We observed significantly higher CO2 emission in AFM (5,335 kg CO2–C ha−1) from June to October, whereas no significant difference was observed among WM (3,480 kg CO2–C ha−1), FM (3,302 kg CO2–C ha−1), AWM (3,877 kg CO2–C ha−1), VWM (3,124 kg CO2–C ha−1) and VFM (3,309 kg CO2–C ha−1), indicating the importance of A. fruticosa along with faba bean residue on CO2 fluxes. As a result, crop residues and land conversion from agricultural to agroforestry can, in turn, influence microbial
biomass, N mineralization, soil C and N content, which can further alter the magnitude of crop growth, soil N2O and CO2 emissions in the present environmental conditions. 相似文献
18.
Improved fallow is a technology that can help to raise agricultural productivity in systems of poor soil fertility and low
financial capital. Models, once calibrated, can be used to investigate a range of improved fallow systems relatively quickly
and at relatively low cost, helping to direct experimental research towards promising areas of interest. Six fallow crop rotations
were simulated using the WaNuLCAS model in a bimodal rainfall setting in Kenya over a 10 year period: (A) alternating fallow
and crop seasons, (B) one season fallow followed by three seasons crop, (C) one season fallow followed by four seasons crop,
(D–F) 1–3 seasons fallow periods followed by 3–5 seasons crop. The strategies were tested using a number of fallow growth
rates, soil clay contents, and rainfall amounts to determine the interaction of fallow rotation and biophysical variables
on maize (Zea mays (L.)) yield and sustainability (organic matter, N2 fixation, leaching). The best simulated fallow strategies doubled maize yield compared to continuous maize over a 10 year
period. Across all biophysical treatments strategy A and B of no more than three consecutive cropping seasons and of one consecutive
fallow season yielded the most maize. This was because fallow benefits were largely due to the immediate fallow soil fertility
benefit (IFB) rather than the cumulative benefit (CFB). The difference in yield between the two strategies was through a balance
between (1) their interaction with the biophysical variables affecting accumulation of organic matter, hence increasing soil
fertility and (2) the extra intrinsic soil fertility used for maize productivity by the inclusion of more cropping seasons
within the rotation. We propose the following conceptual framework to manage fallows for maximum maize yield: when environmental
factors are strongly limiting to fallow and crop growth then fallow strategy A would be the best strategy to employ (less
risk but more labour) and when factors are less limiting then strategy B would be the best to employ. 相似文献
19.
Short-term improved fallow technology, which is characterised by deliberate planting of fast growing N2 fixing legumes species in rotation with crops is currently being promoted for soil fertility replenishment in the small holder farms in the tropics. Recent research and extension efforts on this technology have mainly focused on a narrow range of species. There is a need to evaluate more alternative species in order to diversify the options available to farmers and hence reduce the risks of over dependence on fewer species. We evaluated twenty-two shrubby and herbaceous species for their site adaptability, biomass and nutrient accumulation, biomass quality and maize yield response to soil incorporated plant biomass after the fallow (six and twelve months) in three different field experiments on a Kandiudalfic Eutrudox in western Kenya. Species which yielded large amounts ofthe most biomass N adequate for two to three maize crops were Sesbania sesban, Tephrosia vogelii, Tephrosia candida, Crotalaria grahamiana, Dodonea viscosa, Colopogonium mucunoides, Desmondium uncinatum, Glycine wightii and Macroptilium atropurpureum. Most fallow species tested recycled <22 kg P ha–1 in plant biomass. Significant amounts of K were recycled through plant biomass of Sesbania sesban, Tithonia diversifolia, Tephrosia candida, Crotalaria grahamiana, Dodonea viscosa, Colopogonium mucunoides, Desmondium uncinatum, Glycine wightii, Macroptilium atropurpureum and natural weed fallows. Recyclable K in plant biomass ranged between 4 and 188 kg ha–1Two methods of establishing S. sesban and T. vogelii fallows did not result in significant differences in biomass and nutrient yields at the end of the fallow period. Shrubby species gave Hhigh lignin (>10%) and polyphenol (>2%) concentrations. were found only in the shrubby species, and the (Ppolyphenol + lignin ): N ratio varied widely (0.3–5) amongst the species. evaluated. Maize yield increased by two-fold in the first season following the fallow phase compared with continuous maize for most species. Results suggest that there are a wide variety of legumes that could be used for use in improved fallow technologies aimed at ameliorating nutrient degraded soils and subsequently enhancing crop yields.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
20.
Pascal Danthu Miarantsoa Rakotobe Pascale Mauclère Hanitra Andrianoelisoa Olivier Behra Voninavoko Rahajanirina Barbara Mathevon Eliane Ralembofetra Philippe Collas de Chatelperron 《Agroforestry Systems》2008,72(2):127-135
Fallow with Psiadia altissima is one of the most common post-‘slash and burn’ vegetation successions described in the evergreen forests of eastern Madagascar.
Some fallows consist of almost pure stands of this species, of which the leaves produce an essential oil offering international
commercial interest. The present research aims to evaluate the production potential of essential oil derived from different
fallows rich in P. altissima. The study has revealed that fallows aged 4 and 6 years since the last crop abandonment produce the most essential oil (around
20 l ha−1), but relative to fallow duration, the youngest fallows (1- or 2-year-old) are the most productive, respectively producing
12 and 6 l ha−1 year−1. Additionally, the trees from the youngest fallows have a substantial capacity for regeneration from coppice shoots, on condition
that the cut is performed well above the root collar. Although farmers earn five times less from harvesting leaves than from
cultivating rice from tavy, the possibility is there for them to complement their income and diversify their production. The overall results show that
sustainable exploitation of fallows of P. altissima is a conceivable option. However, this can only be achieved through an integrated approach that takes into account the environmental
and social constraints associated with the development of this new activity. 相似文献