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1.
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
2.
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
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.
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
5.
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
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.
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
8.
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
9.
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
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.
A. Mukuralinda J. S. Tenywa L. Verchot J. Obua N. L. Nabahungu J. N. Chianu 《Agroforestry Systems》2010,80(2):211-221
Green manure of multipurpose trees is known to be a good source of nutrients to crop. However, most agroforestry species do
not have adequate phosphorus (P) in their leaves. Supplementing green manure with moderate dose of P is a beneficial strategy
to improve food security in Rwanda. This study examines the effects of Calliandra
calothyrsus Meissner, Tithonia diversifolia Hensley A.Gray and Tephrosia vogelii Hook.f. green manure applied independently or in combination with triple super phosphate (TSP) and lime on maize yield and
P uptake in the Oxic Tropudalf of Rubona, Rwanda. The treatments were the control, lime at 2.5 t ha−1, TSP at 25 and 50 kg P ha−1, leaf of C. calothyrsus, T. diversifolia, and T. vogelii each at 25 and 50 kg P ha−1, respectively. Leaf shrubs biomass, TSP and lime were applied for four consecutive seasons (2001–2004). The results showed
that the combination of green manure with TSP at a rate of 50 kg P ha−1 significantly increased maize yield from 24 to 508% when compared to the control and T. divesifolia
combined with TSP was leading (508%). Equally, the same treatments as indicated above showed higher P uptake (15.6–18. 6 kg P ha−1) than the control (5 kg P ha−1) and 65% of maize yields variation was explained by total P uptake. The plant residues quality such as C:N ratio, total plant
N, and P significantly influenced the variability of maize grain yields. 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.
Anne Thimonier Elisabeth Graf Pannatier Maria Schmitt Peter Waldner Lorenz Walthert Patrick Schleppi Matthias Dobbertin Norbert Kräuchi 《European Journal of Forest Research》2010,129(3):443-461
Nitrogen (N) deposition exceeds the critical loads for this element in most parts of Switzerland apart from the Alps. At 17
sites (8 broadleaved stands, 8 coniferous stands, and 1 mixed stand) of the Swiss Long-term Forest Ecosystem Research network,
we are investigating whether N deposition is associated with the N status of the forest ecosystems. N deposition, assessed
from throughfall measurements, was related to the following indicators: (1) nitrate leaching below the rooting zone (measured
on a subset of 9 sites); (2) the N nutrition of the forest stand based on foliar analyses (16 sites); and (3) crown defoliation,
a non specific indicator of tree vitality (all 17 sites). Nitrate leaching ranging from about 2 to 16 kg N ha−1 a−1 was observed at sites subjected to moderate to high total N deposition (>10 kg ha−1 a−1). The C/N ratio of the soil organic layer, or, when it was not present, of the upper 5 cm of the mineral soil, together with
the pool of organic carbon in the soil, played a critical role, as previous studies have also found. In addition, the humus
type may need to be considered as well. For instance, little nitrate leaching (<2 kg N ha−1 a−1) was recorded at the Novaggio site, which is subjected to high total N deposition (>30 kg ha−1 a−1) but characterized by a C/N ratio of 24, large organic C stocks, and a moder humus type. Foliar N concentrations correlated
with N deposition in both broadleaved and coniferous stands. In half of the coniferous stands, foliar N concentrations were
in the deficiency range. Crown defoliation tended to be negatively correlated with N concentrations in the needles. In the
majority of the broadleaved stands, foliar N concentrations were in the optimum nutritional range or, on one beech plot with
high total N deposition (>25 kg ha−1 a−1), above the optimum values. There was no correlation between the crown defoliation of broadleaved trees and foliar concentrations. 相似文献
14.
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
15.
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
16.
Myron J. Mitchell 《Journal of Forest Research》2011,16(5):333-340
The relationships of nitrogen biogeochemistry are reviewed, focusing on forested watersheds in North America, Europe and Japan.
Changes in both local and global nitrogen cycles that affect the structure and function of ecosystems are described. Within
northeastern United States and Europe, atmospheric deposition thresholds of ~8 and ~10 kg N ha−1 year−1, respectively, result in enhanced mobilization of nitrate. High nitrate concentrations and drainage water loss rates up to
22 kg N ha−1 year−1 have also been found near Tokyo. Although atmospheric deposition may explain a substantial portion of the spatial pattern
of nitrate in surface waters, other factors also play major roles in affecting the spatial patterns of nitrogen biogeochemistry.
Calcium availability influences the composition of the vegetation and the biogeochemistry of nitrogen. The abundance of sugar
maple is directly linked to soil organic matter characteristics and high rates of nitrogen mineralization and nitrification.
Seasonal patterns of nitrate concentration and drainage water losses are closely coupled with differences in seasonal temperature
and hydrological regimes. Snow-dominated forested catchments have highest nitrate losses during snowmelt. Watersheds in the
main island of Japan (Honshu) with high summer temperatures and precipitation inputs have greatest losses of nitrate occur
during the late summer. Understanding future changes in nitrate concentrations in surface waters will require an integrated
approach that will evaluate concomitantly the influence of both biotic and biotic factors on nitrogen biogeochemistry. 相似文献
17.
Shinji Kaneko Noriko Akieda Fumiya Naito Koji Tamai Yasuhiro Hirano 《Journal of Forest Research》2007,12(1):38-44
Rehabilitated forests established about 100 years ago on denuded lands in a hilly granitic area are widespread in the Kyoto–Osaka
area, the second largest megalopolis in Japan. From 2001 to 2003, we monitored the annual nitrogen (N) budget of a rehabilitated
forest watershed dominated by Quercus serrata and Ilex pedunculosa. The ion concentrations of bulk rain in the watershed were similar to those of other watersheds in Japan. The annual bulk
rain input of N ranged from 5.1 to 6.3 kg N ha−1 year−1, and the N deposition from throughfall and stem-flow ranged from 7.5 to 8.2 kg N ha−1 year−1. Estimated annual outputs of N from the stream ranged from 3.3 to 10.6 kg N ha−1 year−1. These results indicate that the amount of N deposition in this area is less than that in urban Tokyo (>10 kg N ha−1 year−1), but the N output of the watershed is comparable with that of the Tokyo area. We discuss the characteristics of N dynamics
in rehabilitated forests, focusing on the biogeochemical processes of this watershed. 相似文献
18.
Nitrogen inputs from biological nitrogen fixation contribute to productivity and sustainability of agroforestry systems but
they need to be able to offset export of N when trees are harvested. This study assessed magnitudes of biological nitrogen
fixation (natural 15N abundance) and N balance of Acacia mangium woodlots grown in farmer’s fields, and determined if N2 fixation capacity was affected by tree age. Tree biomass, standing litter, understory vegetation and soil samplings were
conducted in 15 farmer’s fields growing A. mangium as a form of sequential agroforestry in Claveria, Misamis Oriental, Philippines. The trees corresponded to ages of 4, 6,
8, 10 and 12 years, and were replicated three times. Samples from different plant parts and soils (0–100 cm) were collected
and analyzed for δ15N and nutrients. The B-value, needed as a reference of isotopic discrimination when fully reliant on atmospheric N, was generated by growing A. mangium in an N2-free sand culture in the glasshouse. Isotopic discrimination occurring during N2 fixation and metabolic processes indicated variation of δ15N values in the order of nodules > old leaves > young leaves > stems > litterfall and roots of the trees grown in the field,
with values ranging from −0.8 to 3.5‰ except nodules which were enriched and significantly different from other plant parts
(P < 0.0001). Isotopic discrimination was not affected by tree age (P > 0.05). Plants grown in N free sand culture exhibited the same pattern of isotopic discrimination as plants grown in the
field. The estimated B-value for the whole plant of A. mangium was −0.86‰. Mature tree stands of 12 years accumulated up to 1994 kg N ha−1 in aboveground biomass. Average proportion of N derived from N2 fixation of A. mangium was 54% (±22) and was not affected by age (P > 0.05). Average yearly quantities of N2 fixed were 128 kg N ha−1 in above-ground biomass amounting to 1208 kg N fixed ha−1 over 12 years. Harvest of 12-year old trees removed approximately 91% of standing aboveground biomass from the site as timber
and fuel wood. The resulting net N balance was +151 kg N ha−1 derived from remaining leaves, twigs, standing litter, and +562 kg N ha−1 when tree roots were included in the calculation. The fast growing A. mangium appears to be a viable fallow option for managing N in these systems. However, other nutrients have to be replaced by using
part of the timber and fuel wood sales to compensate for large amounts of nutrient removed in order for the system to be sustainable. 相似文献
19.
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
20.
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