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1.
Many environmental benefits have been attributed to agroforestry systems in various ecosystems around the world. However, there is a limited amount of information to evaluate this agricultural system in the semi-arid region, specifically in the region of Ceará, Brazil. The objective of this work was to evaluate five agricultural (four agroforestry and one conventional) systems in order to test the hypothesis that the agroforestry systems promote an increase in the soil organic carbon stocks and organic carbon pools, thus improving soil quality. The following treatments were tested: agrosilvopasture (AGP), silvopasture (SILV), traditional agroforestry (TRAG), intensive cropping (IC), and native forest (NF). The soil samples were collected at four depths: 0–6, 6–12, 12–20 and 20–40 cm. Total soil organic carbon stocks and the organic carbon pools (microbial biomass-C, mineralizable-C, oxidizable-C, free, occluded light fraction organic matter, and C in the humic substances) were analyzed. After 5 years of experimental cultivation, the soil under the SILV system presented the best results for the attributes studied, preserving, and in some cases, improving these attributes, when compared to the other conditions. The traditional agroforestry system (TRAG) reduced total organic carbon stocks and, consequently, C in some organic matter compartments, indicating that the fallow period was not sufficient to maintain soil quality. The AGP and IC systems presented significant losses in some of the soil organic matter (SOM) pools, suggesting that the soil environment had been degraded. The most labile SOM components were considered sensitive indicators of change in the soil quality. The silvopasture system can, therefore, be recommended as an alternative soil management strategy for food production and for the maintenance of soil quality and agricultural sustainability in the semiarid region of Ceará state.  相似文献   

2.
The water dynamics of cropping systems containing mixtures of Gliricidia sepium (Jacq.) Walp trees with maize (Zea mays L.) and/or pigeonpea (Cajanus cajan L.) were examined during three consecutive cropping seasons. The trees were pruned before and during each cropping season, but were left unpruned after harvesting the maize; prunings were returned to the cropping area in all agroforestry systems to provide green leaf manure. The hypothesis was that regular severe pruning of the trees would minimise competition with crops for soil moisture and enhance their growth by providing additional nutrients. Neutron probe measurements were used to determine spatial and temporal changes in soil moisture content during the 1997/98, 1998/99 and 1999/00 cropping seasons for various cropping systems. These included gliricidia intercropped with maize, with and without pigeonpea, a maize + pigeonpea intercrop, sole maize, sole pigeonpea and sole gliricidia. Soil water content was measured to a depth of 150 cm in all treatments at 4–6 week intervals during the main cropping season and less frequently at other times. Competition for water was apparently not a critical factor in determining crop performance as rainfall exceeded potential evaporation during the cropping season in all years. The distribution of water in the soil profile was generally comparable in all cropping systems, implying there was no spatial complementarity in water abstraction by tree and crop roots. However, available soil water content at the beginning of the cropping season was generally lower in the tree-based systems, suggesting that the trees continued to deplete available soil water during the dry season. The results show that, under rainfall conditions typical of southern Malawi, the soil profile contains sufficient stored water during the dry season (ca. 75–125 mm) to support the growth of gliricidia and pigeonpea, and that gliricidia trees pruned before and during the cropping season did not deleteriously compete for water with associated crops. Water use efficiency also appeared to be higher in the tree-based systems than in the sole maize and maize + pigeonpea treatments, subject to the proviso that the calculations were based on changes in soil water content rather than absolute measurements of water uptake by the trees and crops.  相似文献   

3.
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   

4.
Soil moisture depletion during dry seasons by planted hedgerows to lower levels than under natural fallow, would reduce drainage and nutrient losses in the following rainy season when food crops are grown. The volumetric water content of the 0–150 cm soil profile was measured under planted hedgerows (alternating Leucaena leucocephala and Gliricidia sepium) and natural fallow, both either annually cropped to sole maize or in a two-year crop/two-year fallow rotation, in the humid forest zone (annual rainfall 1700 mm) of southern Cameroon during the 1995–1996 and 1996–1997 dry seasons. Hedgerows were cut to 0.05 m height, largely eliminating trees’ water consumption during cropping phases. Differences in total soil water content at 0–150 cm depth, between systems, occurred only in the early phases of the 1996–1997 dry season. In both dry seasons, differences between systems in water content were found in some soil layers, all within 0–60 cm depth, yet, without consistent advantage of any system in exploiting the topsoil water resources. Soil water content was lower under L. leucocephala than G. sepium at 20–40 cm depth only. Below 60 cm depth, no differences in water regimes between systems were found. Under southern Cameroonian conditions it is unlikely that any of the systems has an advantage in accessing or recovering water and thus, if available, nutrients from the sub-soil. None of the systems examined was capable of delaying drainage and thus it appears unlikely that downward displacement of nutrients is delayed after the start of the rains.  相似文献   

5.
An on-farm trial was conducted to determine dry matter production of four fodder tree species and their effect on soil water and maize production. The trees were planted in rows intercropped with maize. The four tree species selected were Acacia karroo Hayne (indigenous fodder tree), Leucaena leucocephala (Lam.) De Wit (nitrogen fixing), Morus alba L. (fodder and fruit), and Gleditsia triacanthos L. (fodder and fuel). Volumetric soil water was measured in the upper 0.3 m of soil in each row of the trial using the time domain reflectometry technique. The neutron probe technique was used for monitoring the water content deeper in the soil. Geostatistical methods were used to analyse treatment differences in the upper 0.3 m of soil. The soil water content did not differ significantly between the maize and tree rows indicating that competition for water in the upper horizon was not the reason for lower maize yields. However, at greater soil depths (75–125 cm) trees in the wide spacing used less water than those in the narrow spacing. Light interception was an important factor in reducing maize yields in the row nearest to the trees. High soil water values recorded during summer indicated that in the current cycle of good rainfall the plants in the agroforestry trial were not stressed. Thus the trees do not compete with the crops for soil moisture in good rainfall seasons. However, this study would need further evaluation for the competition for water for the low rainfall years. Since the trees have access to water at greater depths, they are likely to be more productive into the dry season than shallow rooted crops.  相似文献   

6.
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   

7.
This study tested the hypothesis that incorporation of green leaf manure (GLM) from leguminous trees into agroforestry systems may provide a substitute for inorganic N fertilisers to enhance crop growth and yield. Temporal and spatial changes in soil nitrogen availability and use were monitored for various cropping systems in southern Malawi. These included Gliricidia sepium (Jacq.) Walp. trees intercropped with maize (Zea mays L.), with and without pigeonpea (Cajanus cajan L.), sole maize, sole pigeonpea, sole gliricidia and a maize + pigeonpea intercrop. Soil mineral N was determined before and during the 1997/1998, 1998/1999 and 1999/2000 cropping seasons. Total soil mineral N content (NO3− + NH4+) was greatest in the agroforestry systems (p<0.01). Pre-season soil mineral N content in the 0–20 cm horizon was greater in treatments containing trees (≤85 kg N ha−1) than in those without (<60 kg ha−1; p<0.01); however, soil mineral N content declined rapidly during the cropping season. Uptake of N was substantially greater in the agroforestry systems (200–270 kg N ha−1) than in the maize + pigeonpea and sole maize treatments (40–95 kg N ha−1; p<001). Accumulation of N by maize was greater in the agroforestry systems than in sole maize and maize + pigeonpea (p<0.01); grain accounted for 55% of N uptake by maize in the agroforestry systems, compared to 41–47% in sole maize and maize + pigeonpea. The agroforestry systems enhanced soil fertility because mineralisation of the applied GLM increased pre-season soil mineral N content. However, this could not be fully utilised as soil N declined rapidly at a time when maize was too small to act as a major sink for N. Methods for reducing losses of mineral N released from GLM are therefore required to enhance N availability during the later stages of the season when crop requirements are greatest. Soil mineral N levels and maize yields were similar in the gliricidia + maize and gliricidia + maize + pigeonpea treatments, implying that addition of pigeonpea to the tree-based system provided no additional improvement in soil fertility.  相似文献   

8.
This study examined the hypothesis that incorporation of Gliricidia sepium (Jacq.) Walp.) (gliricidia), a fast-growing, nitrogen-fixing tree, into agroforestry systems in southern Malawi may be used to increase the input of organic fertilizer and reduce the need for expensive inorganic fertilizers. The productivity of maize (Zea mays L.), pigeonpea (Cajanus cajan L.) and gliricidia grown as sole stands or in mixed cropping systems was examined at Makoka Research Station (latitude 15° 30′ S, longitude 35° 15′ E) and a nearby farm site at Nazombe between 1996 and 2000. Treatments included gliricidia intercropped with maize, with or without pigeonpea, and sole stands of gliricidia, maize and pigeonpea. Trees in the agroforestry systems were pruned before and during the cropping season to provide green leaf manure. Maize yields and biomass production by each component were determined and fractional light interception was measured during the reproductive stage of maize. Substantial quantities of green leaf manure (2.4 to 9.0 Mg ha−1 year−1) were produced from the second or third year after tree establishment. Green leaf manure and fuelwood production were greatest when gliricidia was grown as unpruned sole woodlots (c. 8.0 and 22 Mg ha−1 year−1 respectively). Improvements in maize yield in the tree-based systems also became significant in the third year, when c. 3.0 Mg ha−1 of grain was obtained. Tree-based cropping systems were most productive and exhibited greater fractional light interception (c. 0.6 to 0.7) than cropping systems without trees (0.1 to 0.4). No beneficial influence of pigeonpea on maize performance was apparent either in the presence or absence of gliricidia at either site in most seasons. However, as unpruned gliricidia provided the greatest interception of incident solar radiation (>0.9), coppicing may be required to reduce shading when gliricidia is grown together with maize. As pigeonpea production was unaffected by the presence of gliricidia, agroforestry systems containing gliricidia might be used to replace traditional maize + pigeonpea systems in southern Malawi. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

9.

• Introduction  

The interactive effects of water and nitrogen (N) on frost hardiness are not well known in broad-leaved trees. Furthermore, new environmental conditions may favour naturally generated hybrids between native and introduced tree species over native species.  相似文献   

10.
Alley cropping systems may influence soil water movement and the water budget because of its complex interactions between crop and tree rooting systems. The objective of this paper was to evaluate water balance and water competition in an alley cropping system, consisting of deciduous tree wild jujube (Choerospondias axillaris) and economic crop peanut (Arachis hypogaea) within subtropical China. Five treatments (20- by 6-m plots) with three replications were included in this study. The treatments were monoculture peanut cropping (P), monoculture younger trees (T1), monoculture older trees (T2), peanut intercropped with younger trees (T1P), and peanut intercropped with older trees (T2P). A multi-layered water balance model, with water movement between soil layers, was implemented by the measurement of soil water potential using sets of tensiometers during the periods from March 1999 to December 2002. The spatial and temporal variations of soil water regime indicated that the trees used soil water below the 60-cm soil depth and alleviated the water stress. The direction of soil water movement indicated that soil water moved to the tree row, which indicated that trees competed with peanuts for water, especially during the seasonal drought period. Water competition was related to the tree spacing and tree age. Compared to the tree monoculture systems, the alley cropping system significantly influenced water budget components and water use patterns, as indicated by the increased evapotranspiration (6–11%), and decreased net drainage (7–45%), water storage (6–29%), and runoff (50–60%). Furthermore, alley cropping systems encouraged the rapid growth of trees, and depressed the biomass and yield of peanuts by 20–50% associated with tree shading effects. The results suggest that competition for water and light must be taken into account when optimizing the alley cropping system.  相似文献   

11.
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   

12.
To address tree–soil–crop interactions in the Sahel, we examined the growth-limiting factors (water, light and mineral nutrients) of Sorghum bicolor growing under trees in agroforestry parklands of Burkina Faso. Growth and yields of sorghum were measured after (1) pruning crowns of Vitellaria paradoxa and Parkia biglobosa trees, and (2) applying mineral fertilizers (nitrogen and/or phosphorus) and supplemental irrigation during normal wet cropping seasons in 2007 and 2008. Irrigation treatments led to non-significant 29% and 23% gains in grain and dry matter yields (from control values of 455 and 1,140 kg ha−1), respectively. The fertilizer showed variable but in general significant increases in grain and straw yields and more consistently in the height of sorghum plants. The crown pruning increased the values of these variables much more strongly, by 520% and 348% (from control, no-pruning values of 282 and 612 kg ha−1), respectively. The growth and production of S. bicolor were also >56% higher under V. paradoxa than under P. biglobosa. The same trends were observed in both cropping seasons, although rainfall was much heavier in 2008 than in 2007, and the mean sorghum grain yield was approximately twice as high in 2008. The results clearly indicate that competition for light limits sorghum growth more than competition for other resources in the studied system, suggesting that parkland management should aim at either increasing light availability (by reducing tree density or pruning) or growing shade-tolerant crops under the trees. However, use of a poorly soluble phosphorus source during the first year, modest amount of water applied through the supplemental irrigation (48 mm) and the wetness of the rainy season in 2008 (which led to abandonment of the irrigation treatments and floods in the experimental plots) may have masked possible effects of the applied fertilizers and irrigation. Therefore, more prolonged analyses of the effects of fertilizers and deficit irrigation are required before robust recommendations can be made to farmers.  相似文献   

13.
The importance of agroforestry systems as carbon sinks has recently been recognized due to the need of climate change mitigation. The objective of this study was to compare the carbon content in living biomass, soil (0–10, 10–20, 20–30 cm in depth), dead organic matter between a set of non-agroforestry and agroforestry prototypes in Chiapas, Mexico where the carbon sequestration programme called Scolel’te has been carried out. The prototypes compared were: traditional maize (rotational prototype with pioneer native trees evaluated in the crop period), Taungya (maize with timber trees), improved fallow, traditional fallow (the last three rotational prototypes in the crop-free period), Inga-shade-organic coffee, polyculture-shade organic coffee, polyculture-non-organic coffee, pasture without trees, pasture with live fences, and pasture with scattered trees. Taungya and improved fallow were designed agroforestry prototypes, while the others were reproduced traditional systems. Seventy-nine plots were selected in three agro-climatic zones. Carbon in living biomass, dead biomass, and soil organic matter was measured in each plot. Results showed that carbon in living biomass and dead organic matter were different according to prototype; while soil organic carbon and total carbon were influenced mostly by the agro-climatic zone (P < 0.01). Carbon density in the high tropical agro-climatic zone (1,000 m) was higher compared to the intermediate and low tropical agro-climatic zones (600 and 200 m, respectively, P < 0.01). All the systems contained more carbon than traditional maize and pastures without trees. Silvopastoral systems, improved fallow, Taungya and coffee systems (especially polyculture-shade coffee and organic coffee) have the potential to sequester carbon via growing trees. Agroforestry systems could also contribute to carbon sequestration and reducing emissions when burning is avoided. The potential of organic coffee to maintain carbon in soil and to reduce emissions from deforestation and ecosystem degradation (REDD) is discussed.  相似文献   

14.
Incorporating cover crops into Christmas tree plantations may potentially improve soil fertility, tree growth and quality and be an alternative to commercial nitrogen (N) fertilizers. However, cover crops may compete with the trees for water and other nutrients than N. This study was carried out to assess whether soil fertility, tree survival and growth could be improved by incorporating leguminous and non-leguminous cover crops into the Fraser fir (Abies fraseri) production system. Dutch white clover (Trifolium pratense), alfalfa (Medicago sativa) and perennial ryegrass (Lolium perenne) were grown in a newly established Fraser fir plantation using two cover crop management practices; no banding (NB) by growing each cover crop throughout the entire plot and banding (B) by creating a 61 cm-wide bare zone centered on the tree rows. A conventionally-managed system (CONV) was used as a control. The cover crop aboveground biomass and N content were assessed. Soil available N (NO3 − and NH4 +) and N mineralization were measured at 0–15, 15–30 and 30–45 cm soil depths. Tree survival, growth, photochemical efficiency of photosystem II (Fv/Fm), branch water potential (Ψw) and foliar nutrients were also evaluated. Biomass production was as high as 13.9, 10.2 and 5.9 Mg DM ha−1 year−1 for clover, alfalfa and ryegrass, respectively. Cover cropping increased soil available N by 1.5- and 2.2-fold relative the CONV in the top soil layer in 2007 and 2008, respectively. Tree seedling survival and growth in the B and CONV systems were similar. In contrast, NB treatments resulted in poor seedling survival and growth relative to the B and CONV plots. Plant Ψw and Fv/Fm decreased significantly for A. fraseri seedlings on the NB treatments relative to their counterparts on the B and CONV plots. However, cover cropping had marginal effects on foliar nutrients. Cover cropping with banding can be an efficient strategy for maintaining productivity in Fraser fir Christmas plantations.  相似文献   

15.
This study examined the effect of alley cropping of Leucaena leucocephala and Faidherbia albida on wood biomass, maize grain yield and soil nitrogen status. The treatments were: trees planted alone at 1 × 5 m spacing; trees intercropped with maize and a sole maize crop. Mulch biomass averaged 6.18 and 0.97 t ha−1 for L. leucocephala and F. albida, respectively. Corresponding wood production was 1.71 and 1.11 t ha−1. Both total N and inorganic N (NO 3 − –N plus 4 + –N) were higher under F. albida and lowest under L. leucocephala. Similarly, foliar N concentration in maize was higher in plots intercropped with F. albida and least in L. leucocephala intercropping. Maize grain yield was little affected by the tree intercrop as competition for resources was reduced through periodic pruning and clean weeding. There was no gain in maize grain yield due to the presence of L. leucocephala and F. albida. These results suggest that alley cropping in Gario is justified for wood production but not for increasing maize grain yield. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

16.
The importance of agroforestry systems in CO2 mitigation has become recognized worldwide in recent years. However, little is known about carbon (C) sequestered in poplar intercropping systems. The main objective of this study is to compare the effects of three poplar intercropping designs (configuration A: 250 trees ha−1; configuration B: 167 trees ha−1 and configuration C: 94 trees ha−1) and two intercropping systems (wheat–corn cropping system and wheat–soybean cropping system) on biomass production and C stocks in poplar intercropping systems. The experiment was conducted at Suqian Ecological Demonstration Garden of fast-growing poplar plantations in northwestern Jiangsu. A significant difference in C concentration was observed among the poplar biomass components investigated (P ≤ 0.05), with the highest value in stemwood and the lowest in fine roots, ranging from 459.9 to 526.7 g kg−1. There was also a significant difference in C concentration among the different crop components (P ≤ 0.05), and the highest concentration was observed in the corn ear. Over the 5-year period, the total poplar biomass increased with increasing tree density, ranging from 8.77 to 15.12 t ha−1, while annual biomass production among the crops ranged from 4.69 to 16.58 t ha−1 in the three configurations. Overall, total C stock in the poplar intercropping system was affected by configurations and cropping systems, and configuration A obtained the largest total C stock, reaching 16.7 t C ha−1 for the wheat–soybean cropping system and 18.9 t C ha−1 for the wheat–corn cropping system. Results from this case study suggest that configuration A was a relative optimum poplar intercropping system both for economic benefits and for C sequestration.  相似文献   

17.
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   

18.
On-farm experiments were conducted in the Philippines to study over a 4-year period the growth of two timber trees, gmelina (Gmelina arborea R. Br.) and bagras (Eucalyptus deglupta Blume), and their impact on the grain yield of intercropped maize. The experiment consisted of maize monocropping plots (control) and maize intercropped between trees planted in block (2 × 2.5 m), and hedgerow arrangement (1 × 10 m). Three maize crops were planted in the block plots before canopy closure, and seven maize crops were planted in the hedgerow and monocropping plots. Maize grain yield in the hedgerow and in the block arrangement with gmelina were respectively 37% (16.58 tons ha−1) and 68% (8.3 tons ha−1) lower than in monocropping (26.21 tons ha−1). In the plots with bagras, maize grain yield in hedgerow and in block arrangement were respectively 19% (24.8 tons ha−1) and 66% (10.4 tons ha−1) lower than in monocropping (30.6 tons ha−1). For both tree species, the diameter at breast height (dbh) was greater in hedgerow than in block arrangement, with the difference being more pronounced with age. It was estimated that gmelina planted in hedgerows would produce 6–8 m3 ha−1 of merchantable volume more than if planted in block. The study verifies the hypothesis that intercropping between widely-spaced trees rows (planted at 10 m or more) is more profitable and feasible to smallholders than either maize monocropping or woodlots, and concludes with recommendations on how to further improve the productivity of tree-intercropping systems.  相似文献   

19.
On-farm experiments were conducted in Khammam district of Andhra Pradesh from 2001 to 2006 to evaluate the biomass productivity, intercrop yields and profitability of Eucalyptus tereticornis clonal and Leucaena leucocephala variety K-636 based systems. Trees were planted at a spacing of 3 × 2 m and evaluated at three locations. Height growth was significantly higher in leucaena during the 4 year where as difference in diameter growth was not significant. Biomass partitioning to the bole was high in case of leucaena, ranged from 83% in 2.5–5 cm diameter at breast height (DBH) trees to 89% in 12.5–15 cm DBH trees and in eucalyptus clones the corresponding values were 71% in 2.5–5 cm DBH trees and 83% in 12.5–15 cm DBH trees. Marketable biomass productivity was higher with leucaena (95 Mg ha−1) in comparison to eucalyptus (87 Mg ha−1). Competition effects of trees on intercrops were observed from the 2 year (2002 post-rainy season). Intercrop yields were 45% of the sole crop in eucalyptus system and 36% in leucaena system during the 2 year. Sole eucalyptus and leucaena plantations and intercropping systems recorded higher gross and net returns over arable cropping. Therefore, it can be concluded that leucaena variety K636 and eucalyptus clonal based agroforestry systems are profitable alternatives to arable cropping under rainfed conditions.  相似文献   

20.
The effect of shoot pruning on leaf phenology, stem wood anatomy and sap flow was investigated on Senna spectabilis (DC.) Irwin and Barneby in Machakos, Kenya. Unpruned trees (single stem) were compared to hedges (two to four stems), pruned 4 times a year during two rainy seasons (April–June, 1997 and November, 1997–January, 1998) separated by a dry season (July–October 1997). Trees attained peak leaf area of 55 m2 plant−1 during the rainy seasons, and shed all their leaves naturally during the dry season. Maximum hedge leaf area was 4 m2 plant−1 between pruning events and 5.2 m2 plant−1 during the dry season. Pruning induced multiple stems and narrow xylem vessels with low hydraulic conductivity. Average cross sectional area of conducting wood per plant was at least 1.8 times greater in trees than in hedges. Xylem lumen diameter at 5 mm depth below the cambium was significantly (P < 0.001) larger in trees (53.6 ± 6.21 μm) than that in hedges (36.2 ± 8.21 μm). Maximum sap flow occurred in the wet season for trees (4800 g d−1 plant−1) and in the dry season for hedges (1400 g d−1 plant−1). Wet season pruning suppressed crown expansion and modified the natural phenology of senna, reducing transpiration rate and therefore soil water depletion, causing crowns to grow. This enhanced the ecological combining ability of senna managed as hedges with annual crops.  相似文献   

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