Poplar leaf biomass distribution and nitrogen dynamics in a poplar-barley intercropped system in southern Ontario, Canada

The effect of hybrid poplar (Populus spp. clone DN 177) leaf biomass distribution on soil nitrification was investigated in two experiments during the 1993, 1994 and 1995 growing seasons in a poplar-barley (Hordeum vulgare cv. OAC Kippen) intercropping experiment established at Guelph, Ontario, Canada. In experiment 1, poplar was intercropped with barley during all three years and the poplar leaves shed during the fall season were removed from the soil surface during 1993 and 1994. In experiment 2, poplar was intercropped with barley in 1993 and with corn (Zea mays cv. Pioneer 3917) in 1994 an 1995, respectively, and the shed poplar leaves were not removed. In experiment 1, the nitrification rates were lower during 1994 and 1995 when the dropped leaves were removed from the field. The total above-ground biomass of barley within 2.5 m of the tree row was 517, 500 and 450 g×m⁻², respectively during the three years, whereas in the middle of the crop row (4–11 m), the corresponding figures were 491, 484 and 464 g×m–2. Mean nitrification rates, N availability and carbon content were higher in soils close to the poplar tree rows (2.5 m) compared to the corresponding values in the middle of the crop alley (4–11 m from the tree row). In experiment 2, where poplar leaves were not removed from the field, nitrification rates in soils within 2.5 m distance from the poplar row were fairly constant (range 100 to 128 μg 100 g⁻¹ dry soil day⁻¹) during the three years. Results suggest that soil nitrification rates, soil carbon content and plant N uptake adjacent to the poplar tree rows are influenced by poplar leaf biomass input in the preceding year. This revised version was published online in June 2006 with corrections to the Cover Date.     

Interactions amongst trees and crops in <Emphasis Type="Italic">taungya</Emphasis> systems of western Kenya

Lack of empirical data on the effects of the taungya system on establishment and early growth of softwood plantations have partly contributed to controversial decisions regarding the continued suitability of the system for plantation establishment in Kenya. This study examined effectiveness of taungya systems of forest plantation establishment using Cupressus lusitanica and Pinus patula trees with Zea mays (maize) as a test intercrop on two contrasting site types (deep and shallow soils) in Mt. Elgon forest, western Kenya . Four treatments were evaluated in each site: trees with or without weed control, trees intercropped with maize, and sole maize. Results showed that tree survival, growth and nutrient uptake, and maize growth and yield were higher in the deep soil site than the shallow site. The t aungya system improved tree survival and growth, effects being greater in the deep than the shallow soil site. Both Cupressus lusitanica and Pinus patula trees had the same effects on maize growth and yield, reducing maize growth by 41–48% in the deep soil sites, and by 16–26% in the shallow site. Vector nutrient analysis and vector competition analysis of the treatment effects on growth and nutrient uptake of the trees and the maize crop suggested competition for N on the deep soils, but competition for K and P on the shallow soils. The study has demonstrated the applicability of graphical vector competition analysis in diagnosing tree–crop interactions in agroforestry.     

海南尖峰岭地区三种热带复合农林业体系效益研究

对海南岛尖峰岭地区热带珍贵树种母生、海南石梓人工林下种植经济作物益智、咖啡的复合农林业系统的生态和经济效益研究表明：复合系统能显著促进主林层乔木的生长,胸径生长速度比对照地高出４３％～１３４％,材积生长高出１８％～８１％,生物量高出５％～８６％;生物量净积累量９．５３～１５．２３ｔ·ｈｍ－２·ａ－１,为对照地的１．６～５．１倍;系统的光能利用率为０．７８％～１．２６％,为对照样地的１．９４～５．０４倍;同时系统具有较高的经济效益,林下种植益智后的产值可达１．８～３万元·ｈｍ－２·ａ－１,为对照地的５．２６～９．８２倍,投入产出比为１∶２．９３～１∶４．１７。     

Characteristics of carbon and nitrogen of soil microbial biomass and their relationships with soil nutrients in Cunninghamia lanceolata plantations

The soil microbial biomass and nutrient status under the native broadleaved forest and Cunninghamia lanceolata plantations at the Huitong National Research Station of Forest Ecosystem (in Hunan Province, midland of China) were examined in this study. The results showed that after the native broadleaved forest was replaced by mono-cultured C. lanceolata or C. lanceolata, soil microbial biomass and nutrient pool decreased significantly. In the 0–10 cm soil layer, the concentrations of soil microbial carbon and nitrogen in the broadleaved forest were 800.5 and 84.5 mg/kg, respectively. These were 1.90 and 1.03 times as much as those in the first rotation of the C. lanceolata plantation, and 2.16 and 1.27 times as much as those in the second rotation of the plantation, respectively. While in the 10–20 cm soil layer, the microbial carbon and nitrogen in the broadleaved forest were 475.4 and 63.3 mg/kg, respectively. These were 1.86 and 1.60 times as much as those in the first rotation, and 2.11 and 1.76 times as much as those in the second rotation, respectively. Soil nutrient pools, such as total nitrogen, total potassium, NH₄ ⁺-N, and available potassium, also declined after the C. lanceolata plantation replaced the native broadleaved forest, or Chinese fir was planted continuously. Less litter and slower decay rate in pure Chinese fir plantation were the crucial factors leading to the decrease of soil microbial biomass and nutrient pool in this area. Human disturbance, especially slash-burning and site preparation, was another factor leading to the decrease. There were significant positive correlations between soil microbial carbon and nitrogen and soil nutrients. To improve soil quality and maintain sustainable productivity, some measures, including planting mixed conifer with hardwood, preserving residues after harvest, and adopting scientific site preparation, should be taken. Translated from Chinese Journal of Applied Ecology, 2006, 17(12): 2,292–2,296 [译自: 应用生态学报]     

Intercropping system of tropical leguminous species and Eucalyptuscamaldulensis, inoculated with rhizobia and/or mycorrhizal fungi in semiarid Brazil

For the purpose of reforestation and wood supply the leguminous tree Anadenanthera peregrina, a native species, was intercropped with Eucalyptus camaldulensis in a degraded semiarid area of Brazil. Single and mixed stands of these species were inoculated with Rhizobium and/or arbuscular mycorrhizal fungi (AMF). The growth of all species in mixed stands did not differ from those cultivated in monoculture and land equivalent ratio (LER) exceeded unity in intercropped plots. Inoculated plants showed greater height and diameter growth and dry matter and nutrient concentration in plants of A. peregrina was higher in inoculated single plots. The distribution, composition and density of AMF species was related to the rhizosphere effect of plant species. The intercropped model where all the plants were inoculated achieved soil AMF diversity patterns similar to those of the preserved area and showed also higher soil organic matter, nutrient content as well as a reduction in soil macroporosity. This model of intercropping may be considered as an efficient system for reforestation under semiarid conditions.     

Using agroforestry to improve soil fertility: effects of intercropping on <Emphasis Type="Italic">Ilex paraguariensis</Emphasis> (yerba mate) plantations with <Emphasis Type="Italic">Araucaria angustifolia</Emphasis>

This study assessed the use of agroforestry to improve soil nutrient properties in plantations containing Ilex paraguariensis St. Hilaire (yerba mate). Intercropping within tree plantation systems is widely practiced by farmers around the World, but the influence of different species combinations on system performance still requires further investigation. I. paraguariensis is a major South American crop commonly cultivated in intensive monocultures on low activity clay soils, which are highly prone to nutrient deficiencies. Study plots were established in 20 plantations in Misiones, Argentina. These involved two species combinations (I. paraguariensis monoculture and I. paraguariensis intercropped with the native tree species Araucaria angustifolia) and two age classes (30 and 50 years old). Chemical soil samples were analysed to determine Ca, Mg, K, P, N, C and Al concentrations, effective CEC (eCEC) and pH at two soil depths (0–5 cm and 5–10 cm). In the younger plantations, the agroforestry sites had lower nutrient levels than I. paraguariensis monoculture sites. However, the monoculture plantations were more susceptible than agroforestry sites to a decline in soil nutrient status over time, particularly with respect to Ca, eCEC, N and C for both soil depths. P concentrations were below detection limits for all sites, potentially reflecting the high P-fixing capacity of the kaolinic soils of this region. While agroforestry systems may be better at maintaining soil quality over time, significant growth increase of I. paraguariensis was apparent only for the monoculture sites.     

Effects of intercropping systems of trees with soybean on soil physicochemical properties in juvenile plantations

The intercropping system of tree with soybean in juvenile plantations, as a short-term practice, was applied at Lao Shan Experimental Station in Mao’er Shan Forest of Northeast Forestry University, Harbin, China. The larch (Larix gmelinii)/soybean (Glycine max.) and ash (Fraxinus mandshurica) intercropping systems were studied in the field to assess the effects of the intercropping on soil physicochemical properties. The results showed that soil physical properties were improved after soybean intercropping with larch and ash in one growing season. The soil bulk density in larch/soybean and ash/soybean systems was 1.112 g·cm⁻³ and 1.058 g·cm⁻³, respectively, which was lower than that in the pure larch or ash plantation without intercropping. The total soil porosity also increased after intercropping. The organic matter amount in larch/soybean system was 1.77 times higher than that in the pure larch plantation, and it was 1.09 times higher in ash/soybean system than that in the pure ash plantation. Contents of total nitrogen and hydrolyzable nitrogen in larch/soybean system were 4.2% and 53.0% higher than those in the pure larch stand. Total nitrogen and hydrolyzable nitrogen contents in ash/soybean system were 75.5% and 3.3% higher than those in the pure ash plantation. Total phosphorus content decreased after intercropping, while change of available phosphorus showed an increasing trend. Total potassium and available potassium contents in the larch/soybean system were 0.6% and 17.5% higher than those in the pure larch stand. Total potassium and available potassium contents in the ash/soybean system were 56.4% and 21.8% higher than those in the pure ash plantation. Biography: FAN A-nan (1972–), female, Ph. Doctor in Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, P. R. China.     

Water use assessment in alley cropping systems within subtropical China

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.     

Intercropping Acacia albida with maize (Zea mays) and green gram (Phaseolus aureus) at Mtwapa,Coast Province,Kenya

Long-term agroforestry demonstrations/trials using Acacia albida and other nitrogen fixing multipurpose trees/shrubs were initiated in mid-1982 to assess soil and crop productivity at a coastal lowland site characterized by low soil fertility, weed problems and consequent poor crop yields. Growth performance (height and diameter at breast height, dbh) of Acacia albida under eight densities rotationally intercropped with maize (Zea mays) and green gram (Phaseolus aureus), crop grain yields, soil fertility changes and weed control were assessed for a 5-year period (May 1982 to March 1987). A parallel-row systematic spacing field layout was used. Intercropped Acacia albida mean hight and dbh were 140 and 24% respectively higher than tree-only controls by the fifth year. Growth rate was low during the first year but increased in subsequent years to mean height and dbh of 9 m and 10 cm respectively by March 1987. While differences in dbh were significant, those between stand heights were not. Crop yields, especially under higher tree densities, declined considerably due to unexpected shade which also caused significant reductions in weed biomass. Soil fertility levels remained unchanged during the experimental period relative to the initial status, and differences between the intercropped Acacia albida plots and the tree — or crop — only control appeared not to be significant. We conclude that an understanding of the mechanism regulating leaf fall/retention phenomena of Acacia albida is crucial towards determining the intercropping potentials of the species.     

Improving the Traditional Acacia Senegal-Crop System in Sudan: The Effect of Tree Density on Water Use, Gum Production and Crop Yields

The traditional Acacia senegal bush-fallow in North Kordofan, Sudan, was disrupted and the traditional rotational fallow cultivation cycle has been shortened or completely abandoned, causing decline in soil fertility and crop and gum yields. An agroforestry system may give reasonable crop and gum yields, and be more appealing to farmers. We studied the effect of tree density (266 or 433 trees ha⁻¹) on two traditional crops; sorghum (Sorghum bicolor) early maturing variety and karkadeh (Hibiscus sabdariffa), with regard to physiological interactions, yields and soil water depletion. There was little evidence of complementarity of resource sharing between trees and crops, since both trees and field crops competed for soil water from the same depth. Intercropping significantly affected the soil water status, photosynthesis and stomatal conductance in trees and crops. Gum production per unit area increased when sorghum was intercropped with trees in low or high density. However, karkadeh reduced the gum yield significantly at high tree density. Yields of sorghum and karkadeh planted within trees of high density diminished by 44 and 55% compared to sole crops, respectively. Intercropping increased the rain use efficiency significantly compared to trees and field crops grown solely. Karkadeh appears to be more appropriate for intercropping with A. senegal than sorghum and particularly recommendable in combination with low tree density. Modification of tree density can be used as a management tool to mitigate competitive interaction in the intercropping system.     

Soil organic carbon and aggregation under poplar based agroforestry system in relation to tree age and soil type

The poplar based agroforestry system improves aggregation of soil through huge amounts of organic matter in the form of leaf biomass. The extent of improvement may be affected by the age of the poplar trees and the soil type. The surface and subsurface soil samples from agroforestry and adjoining non-agroforestry sites with different years of poplar plantation (1, 3 and 6 years) and varying soil textures (loamy sand and sandy clay) were analyzed for soil organic carbon, its sequestration and aggregate size distribution. The average soil organic carbon increased from 0.36 in sole crop to 0.66% in agroforestry soils. The increase was higher in loamy sand than sandy clay. The soil organic carbon increased with increase in tree age. The soils under agroforestry had 2.9–4.8 Mg ha⁻¹ higher soil organic carbon than in sole crop. The poplar trees could sequester higher soil organic carbon in 0–30 cm profile during the first year of their plantation (6.07 Mg ha⁻¹ year⁻¹) than the subsequent years (1.95–2.63 Mg ha⁻¹ year⁻¹). The sandy clay could sequester higher carbon (2.85 Mg ha⁻¹ year⁻¹) than in loamy sand (2.32 Mg ha⁻¹ year⁻¹). The mean weight diameter (MWD) of soil aggregates increased by 3.2, 7.3 and 13.3 times in soils with 1, 3 and 6 years plantation, respectively from that in sole crop. The increase in MWD with agroforestry was higher in loamy sand than sandy clay soil. The water stable aggregates (WSA >0.25 mm) increased by 14.4, 32.6 and 56.9 times in soils with 1, 3 and 6 years plantation, respectively, from that in sole crop. The WSA >0.25 mm were 6.02 times higher in loamy sand and 2.2 times in sandy clay than in sole crop soils.     

Sand-fixing effects of Caragana microphylla shrub in Horqin sandy land, North China

In the semi-arid Horqin sandy land of north China, Caragana microphylla, a leguminous shrub, is the dominant plant species and is widely used in vegetation reestablishment programs to stabilize shifting sand. The sand-fixing effects of 6-and 11-year-old C. microphylla plantations were studied. The results showed that: 1) the wind velocity and sand transport rate in the plantation were less than those in dunes; 2) the air temperature in the plantation was lower than those in dunes. Relative humidity was higher and the soil temperature was lower, which benefits plant growth; 3) the physical and chemical characteristics of soil were improved to some extent over age. The porosity and percentage of tiny sand (diameter 0.05–0.1 mm) and clay particle (diameter < 0.05 mm) increased, bulk density in surface soil decreased, and saturated water-holding capacity improved. Organic C, total N, available N and available K content increased gradually, and soil fertility was enhanced. __________ Translated from Journal of Soil and Water Conservation, 2007, 21(1): 84–87 [译自: 水土保持学报]     

Beneficial Effects of Intercropping on the Growth and Nitrogen Status of Young Wild Cherry and Hybrid Walnut Trees

Growing concern for economic and environmental issues emphasizes the potential value of intercropping systems in temperate regions. However, the selection of relevant tree species to be associated with crops has been little documented. The growth and the nitrogen nutrition of two economically valuable species, wild cherry (Prunus avium L.) and hybrid walnut (Juglans nigra L.×Juglans regia L.), were compared over six years after plantation. These two species were associated with non-irrigated cereal crops in the agroforestry treatment or grown separately (weeded control and fallow). Intercropping increased diameter growth as soon as year 2 in the two species. Leaf biomass assessment using allometric models showed an earlier and greater leaf biomass increase in hybrid walnut than in wild cherry tree. After six years, the relative growth increase of the agroforestry trees with respect to the control trees varied with the parameter considered (diameter at breast height from +26 to +65%, leaf biomass from +54 to +142%) and with the tree species (higher relative growth for hybrid walnut trees). The beneficial effect on tree growth can be accounted for in terms of enhanced nitrogen nutrition. The tree–crop association in intercropping systems, which improves tree growth, might thus allow the planting of more demanding trees on soils of lower fertility.     

Soil water dynamics in cropping systems containing <Emphasis Type="Italic">Gliricidia sepium</Emphasis>, pigeonpea and maize in southern Malawi

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.     

Role of canopy interception on water and nutrient cycling in Chinese fir plantation ecosystem

The role of canopy interception on nutrient cycling in Chinese fir plantation ecosystem was studied on the basis of the position data during four years. Results indicate that the average canopy interception amount was 267.0 mm/year. Canopy interception play a significant role in water cycle and nutrient cycle processes in ecosystem, and was an important part of evaporation from the Chinese fir plantation ecosystem, being up to 27.2%. The evaporation from the canopy interception was an important way of water output from ecosystem, up to 19.9%. The flush-eluviation of branches and leaves caused by canopy interception brought nutrient input of 143.629 kg/(hm² · year), which was 117.2% of the input 63.924 kg/(hm² · year) from the atmospheric precipitation. The decreased amount of 80.1 mm precipitation input caused by canopy interception reduced the amount of rainfall into the stand surface and infiltration into the soil, reduced the output with runoff and drainage, and decreased nutrient loss through output water. Therefore, the additional preserve of nutrient by canopy interception was 8.664 kg/(hm² · year). __________ Translated from Scientia Silvae Sinicae, 2006, 42(12): 1–5 [译自: 林业科学]     

Alley cropping on an Ultisol in subhumid Benin. Part 1: Long-term effect on maize, cassava and tree productivity

In southern Benin, West Africa, two alley cropping systems were studied from 1986 to 1992. Yield development was followed in a maize and cassava crop rotation vs. intercropping system, with alleys of Leucaena leucocephala (Lam.) de Wit and Cajanus cajan (L.) Millsp. vs. a no-tree control, with and without NPK fertiliser. Without alleys, NPK fertilisation maintained high yield levels of 2–3 t maize dry grain plus 4–6 t ha^–1 cassava root DM in intercropping, 3–4 t ha^–1 maize and 6–10 t ha^–1 cassava in solercropping. Without NPK, final yields seemed to stabilise at about 1 t maize plus 2 t cassava in intercropping and twice as much in each solecrop. Alley cropping induced significant yield increases by about 50% with both tree species in unfertilised, intercropped maize, and with Cajanus in fertilised, solecropped cassava. In monetary terms, the NPK-fertiliser response of stabilised yields was significant for all treatments except the solecropped Leucaena alleys. It is concluded that on Ultisols with low nutrient status in the upper rooting zone, alley cropping with low-competitive tree species may improve food crop yields but the greatest monetary output is achieved by intercropping with mineral fertiliser independent of the presence or absence of an agroforestry component.     

内蒙古大青山前坡油松人工林生长特征研究

以内蒙古大青山前坡38 a生、17 a生油松人工林为研究对象,对林分生长特征、部分立地因子特征进行调查分析,研究造林立地因子对人工林生长的影响.结果表明:(1)38 a生油松人工林平均树高、胸径和冠幅分别为7.36 m、9.8 cm和261.1 cm;17 a生油松人工林平均树高、胸径和冠幅分别为2.86 m、8.1 ...     

Soil properties under young Chinese fir-based agroforestry system in mid-subtropical China

In order to decrease the soil nutrient loss in young planted Chinese fir (Cunningharnia lanceolata (Lamb.) Hook.) forestland and to investigate the impact of young Chinese fir plantation intercropped with crops on soil quality, a field experiment was set up in the mid-subtropics of China in 1998. The effects of growing crops in combination with young Chinese fir on soil properties were evaluated by measuring physico-chemical, microbiological and biochemical parameters five years after the beginning of this experiment. Three treatments were selected in the experiment, i.e., Chinese fir plantation intercropped with peanut (Arachis hypogaea L.) -wheat (Triticum aestivum L.) cropping sequence (C-P/W); Chinese fir plantation intercropped with maize (Zea mays L.)-wheat cropping sequence (C-M/W) and only Chinese fir plantation (Control). Soils were sampled at the 0–10 cm depth in 2003. The increases in soil nutrients (especially with respect to soil available nutrients), soil microbial biomass C (SMBC), microbial quotient (MQ), soil basal respiration (SBR), microbe numbers and enzyme activities and slight decrease in metabolic quotient (qCO₂) as well as melioration in soil structure and humus quality were observed in tree-crop combinations compared with sole plantation of Chinese fir, although the differences were not always statistically significant. In addition, the evidence obtained from this study also suggests that Chinese fir-crop combination can promote the growth of young Chinese fir. Therefore, growing crops in combination with young Chinese fir can be considered a good forest management practice, helping to limit the gradual depletion of soil nutrients and, at the same time, to some degree controlling the degradation of planted Chinese fir forestland.     

Structure and Function of <Emphasis Type="Italic">Populus deltoides</Emphasis> Agroforestry Systems in Eastern India: 2. <Emphasis Type="Italic">Nutrient dynamics</Emphasis>

Nutrient concentrations in plant and soil and their rates of cycling in poplar (Populus deltoides)-based agroforestry systems were studied at Pusa, Bihar, India. The nutrient concentrations in the standing biomass of the crop were more than those in tree, whereas the nutrient contents showed the reverse trend. Soil, litter and vegetation accounted for 80.3–99.5, 0.1–5.0 and 0.4–14.7%, respectively, of the total nutrients in the system. Considerable reduction (40–54%) in concentration of nutrients in leaves occurred during senescence. The uptake of nutrients by vegetation, and also by different components with and without adjustment for internal recycling, were calculated separately. Annual transfer of litter nutrient to the soil by vegetation was 37.3–146.2 N, 5.6–17.9 P and 25.0–66.3 K kg ha⁻¹ year⁻¹ in young (3-year-old) and mature (9-year-old) plantations. Turnover rate and time for different nutrients ranged between 0.86–0.99 year⁻¹ and 1.01–1.16 years, respectively. Compartmental models for nutrient dynamics have been developed to represent the distribution of nutrient contents and net annual fluxes within the system. This study shows that the poplar-based agroforestry system can be sustainable in terms of soil nutrient status.     

Characteristics of root growth in a fast-growing and high-yield poplar plantation under subsurface drip-irrigation

The characteristics of root growth in the fast-growing and high-yield plantation of poplar I-214 (Populus × euramericana cv. ‘I-214’) were studied under two contrasting conditions, subsurface drip-irrigation (SDI) and normal irrigation (CK), on the sandy soil of Chaobai River, Beijing. The results showed that in the soil layer of 20–50 cm, there was a considerable increase in the amount of roots less than 10 mm in diameter (especially those of less than 2mm) under SDI, which was three times as much as that under CK. The absorbing roots under SDI were concentrated in the soil layer of 20–50 cm, while the roots under CK were distributed evenly in each layer. With respect to horizontal distribution, roots (d<10 mm) under SDI were distributed mainly near the subsurface emitters and the amount of roots in 3 m in a row under SDI were 50% less than under CK. Therefore, it is suggested that subsurface emitters with the shape of “#” should be collocated in the middle of two rows and two individual trees to increase the distributing and absorbing range of roots under SDI, and further increase the plantation productivity. __________ Translated from Journal of Beijing Forestry University, 2007, 29(2): 34–40 [译自: 北京林业大学学报]