Effects of intercropping with Atractylodes lancea and application of bio-organic fertiliser on soil invertebrates,disease control and peanut productivity in continuous peanut cropping field in subtropical China

The consecutive monoculturing of peanut seriously affects its yield and quality in the red soil regions of southern China. Different control measures for consecutively monocultured peanut fields should be explored to ensure the sustainable development of the local peanut industry. In this study, the influence of two different regimes, the intercropping of peanut with Atractylodes lancea and the furrow application of bio-organic fertiliser (BOF), on the community composition of soil invertebrates, the severity of peanut disease and peanut productivity was evaluated in an upland region where peanut had been monocropping for 5 years. We found that intercropping with A. lancea and the furrow application of BOF significantly changed the community composition of soil invertebrates and increased their biodiversity, as estimated by the Shannon and Simpson indices. Intercropping with A. lancea significantly reduced the proportion of Collembola, such as Tullbergia, Onychiurus, Folsomia and Folsomina, while the furrow application of BOF significantly increased the abundance of Collembola, such as Isotomidae compared with conventional monoculture. The intercropping significantly increased the proportion of Acarina, such as Mesostigmata and Oribatida, whereas the furrow application of BOF did not increase this proportion compared to conventional monoculture. The intercropping and application of BOF significantly reduced the damping-off in seedling and root rot disease at the maturation stage and increased peanut yield. The leaf spot disease of peanut was significantly suppressed by the intercropping but not by the application of BOF. The results of the study suggested that the intercropping of peanut with A. lancea and the furrow application of BOF could effectively relieve the problems associated with consecutive monoculture of peanut in the red soil regions of southern China.     

Influence of Acacia senegal agroforestry system on growth and yield of sorghum, sesame, roselle and gum in north Kordofan State, Sudan

We examined the effects of intercropping with Acacia senegal (L.) Willd on growth and yield of sorghum (Sorghum bicolor L.), sesame (Sesamum indicum L.) and roselle (Hibiscus sabdariffa). Field experiments were conducted in El-Obeid Research farm (13°10’ N; 30°12’ E), North Kordofan State, Sudan, during 2002 2003 in an 11-year-old A. senegal plantation. The experimental design was randomized complete block design (RCBD) with four replications. Data were recorded for plant height (cm), fresh weight (kg ha -1 ), dry weight (kg ha -1 ), crop yield (kg ha -1 ), and gum yield (kg ha -1 ). We used Land Equivalent Ratios (LER) and simple financial analyses of gross surpluses to evaluate the productivity and profitability of the different treatments. The results indicated that A. senegal trees had a beneficial effect on crop performance and yield as well as gum yield. Significant differences (p<0.05) were obtained for plant height, fresh weight, dry weight and crop yield. Therefore, yield of sorghum, sesame and roselle under intercropping system were 13.7%, 23.8% and 20.9% higher than that obtained in the sole cropping system respectively. The highest yield increase was observed with sesame (23.8%). Gum yield (g/tree/picking) was signifi- cantly (p<0.05) increased for sorghum, sesame and roslle under inter-cropping system. The highest yield of (298g/tree/picking) was obtained when roselle was intercropped with A. senegal, while the least gum yield of (239 g tree-1 ) was recorded in pure A. senegal plot. All the treatments gave land equivalent ratio (LER) of more than one-indicating the superiority of growing the field crops in intercropping over the sole cropping systems. The highest LER of 3.8 was obtained for sesame intercropped with A. senegal (Hashab), followed by 3.7, when sorghum was intercropped with A. senegal and 3.3 when roselle intercropped with A. senegal. All the treatments gave positive net revenues, the highest being for intercropped sorghum (558 SDG ha -1 ) (SDG=Sudanese gienh). The intercropping of roselle gave the second net revenue (518 SDG ha -1 ),while the sole sorghum gave the lowest net revenue (501 SDG ha -1 ).     

Effects of <Emphasis Type="Italic">Acacia seyal</Emphasis> and biochar on soil properties and sorghum yield in agroforestry systems in South Sudan

We studied the effects of Acacia seyal Del. intercropping and biochar soil amendment on soil physico-chemical properties and sorghum (Sorghum bicolor L.) yields in a two-year field experiment conducted on a silt loam site near Renk in South Sudan. A split-plot design with three replications was used. The main factor was tree-cropping system (dense acacia + sorghum, scattered acacia + sorghum, and sole sorghum) and biochar (0 and 10 Mg ha^?1) was the subplot factor. The two acacia systems had lower soil pH, N and higher C/N ratios compared to the sole sorghum system. Biochar significantly increased soil C, exchangeable K⁺ contents, field capacity and available water content, but reduced soil exchangeable Ca²⁺ and effective CEC, and had no effect on soil pH. Acacia intercropping significantly reduced sorghum grain yields while biochar had no significant effect on sorghum yields. The land equivalent ratio (LER) for sorghum yield was 0.3 for both acacia systems in 2011, with or without biochar, but increased in 2012 to 0.6 for the scattered acacia system when combined with biochar. The reduction in sorghum yields by the A. seyal trees was probably due to a combination of competition for water and nutrients and shading. The lack of a yield response to biochar maybe due to insufficient time or too low a dosage. Further research is needed to test for the effects of tree intercropping and biochar and their interactions on soil properties and crop yields in drylands.     

Estimation of net gain of soil carbon in a nitrogen-fixing tree and crop intercropping system in sub-Saharan Africa: results from re-examining a study

Nitrogen (N)-fixing tree and crop intercropping systems can be a sustainable agricultural practice in sub-Saharan Africa and can also contribute to resolving climate change through enhancing soil carbon (C) sequestration. A study conducted by Makumba et al. (Agric Ecosyst Environ 118:237?C243, 2007) on the N-fixing tree gliricidia and maize intercropping system in southern Malawi provides a rare dataset of both sequestered soil C and C loss as soil carbon dioxide (CO₂) emissions. However, no soil C gain and loss estimates were made so the study failed to show the net gain of soil C. Also absent from this study was potential benefit or negative impact related to the other greenhouse gas, nitrous oxide (N₂O) and methane (CH₄) emissions from the intercropping system. Using the data provided in Makumba et al. (Agric Ecosyst Environ 118:237?C243, 2007) a C loss as soil CO₂ emissions (51.2?±?0.4?Mg?C?ha^?1) was estimated, amounting to 67.4% of the sequestered soil C (76?±?8.6?Mg?C?ha^?1 in 0?C2?m soil depth) for the first 7?years in the intercropping system. An annual net gain of soil C of 3.5?Mg?C?ha^?1?year^?1 was estimated from soil C sequestered and lost. Inclusion of the potential for N₂O mitigation [0.12?C1.97?kg?N₂O?CN?ha^?1?year^?1, 0.036?C0.59?Mg CO₂ equivalents (eq.) ha^?1?year^?1] within this intercropping system mitigation as CO₂ eq. basis was estimated to be 3.5?C4.1?Mg CO₂ eq.?ha^?1?year^?1. These results suggest that reducing N₂O emission can significantly increase the overall mitigation benefit from the intercropping system. However, significant uncertainties are associated with estimating the effect of intercropping on soil N₂O and CH₄ emissions. These results stress the importance of including consideration of quantifying soil CO₂, N₂O and CH₄ emissions when quantifying the C sequestration potential in intercropping system.     

Growing woody biomass for bioenergy in a tree-based intercropping system in southern Ontario, Canada

During the spring of 2006, three willow varieties (SV1, SX67 and 9882-41) were established on marginal land in an agroforestry tree-intercropping arrangement where plots of short rotation willows were planted between rows (spaced 15?m apart) of 21-year-old mixed tree species. As a control, the same varieties were established on an adjacent piece of land without established trees (conventional willow system). This study investigated the magnitude of carbon pools, fine root and leaf biomass inputs and clone yields in both the tree-based intercropping (agroforestry) and conventional monocropping systems. Willow biomass yield was significantly higher in the agroforestry field (4.86?odt?ha^?1?y^?1) compared to the conventional field (3.02?odt?ha^?1?y^?1). In both fields, varieties SV1 and SX67 produced higher yields than the variety 9882-41. Willow fine root biomass in the top 20?cm of soil was significantly higher in the intercropping system (3,062?kg?ha^?1) than in the conventional system (2,536?kg?ha^?1). Differences in fine root biomass between clones were similar to that observed for differences in biomass yield: SV1?>?SX67?>?9882-41. Leaf input was higher in the intercropping system (1,961?kg?ha^?1) than in the conventional system (1,673?kg?ha^?1). Clonal differences in leaf inputs followed the same trends as those for root biomass and yield: SV1?>?SX67?>?9882-41. Soil organic carbon was significantly higher in the agroforestry field (1.94?%) than in the conventional field (1.82?%). A significant difference in soil organic carbon was found between the three clones: soils under clone 9882-41 had the lowest soil organic carbon at 1.80?%.     

Carbon stocks and biomass production of three different agroforestry systems in the temperate desert region of northwestern China

Carbon sequestration potential of agroforestry systems has attracted worldwide attention following the recognition of agroforestry as a greenhouse gas mitigation strategy. However, little is known about carbon stocks in poplar–maize intercropping systems in arid regions of China. This study was conducted in the temperate desert region of northwestern China, a region with large area of poplar–maize intercropping systems. The objective of this study was to assess biomass production and carbon stock under three poplar–maize intercropping systems (configuration A, 177 trees ha^?1; configuration B, 231 trees ha^?1; and configuration C, 269 trees ha^?1). We observed a significant difference in the carbon stock of poplar trees between the three configurations, with the highest value of 36.46 t ha^?1 in configuration C. The highest carbon stock of maize was achieved in configuration B, which was significantly higher than configuration A. The grain yield was highest in configuration A, but there was no significant difference from the other two configurations. In the soil system (0–100 cm depth), the total carbon stock was highest in configuration C (77.37 t ha^?1). The results of this study suggest that configuration C is the optimum agroforestry system in terms of both economic benefits and carbon sequestration.     

Overstory-specific effects of litter fall on the microbial carbon turnover in a mature deciduous forest

Mature deciduous forests can serve as important carbon (C) sinks, but the C storage differs significantly in dependency on the tree species. To specify the significance of overstory-specific effects of litter fall on the soil microbial C turnover, we have investigated the ¹³C isotopic signature of microbial biomarker phospholipid fatty acids (PLFAs). Samples were taken under pure Fagus sylvatica and mixed overstory (F. sylvatica and Fraxinus excelsior or F. excelsior, Acer spp. and F. sylvatica) in a mature temperate deciduous forest in Central Germany 4 weeks prior to and 3 weeks after litter fall. Accordingly, the CO₂ emission from soil was measured before, during and after the litter fall to investigate the response of decomposition. At all sites and at both sampling dates the fungal biomarker PLFA 18:2ω6,9 had predominantly lower δ¹³C values (from −32 to −43‰) than the bacterial biomarker PLFAs (δ¹³C values from −23 to −39‰). This difference indicated that fungi generally used preferentially plant derived C, whereas the bacterial populations include groups which used SOM derived C, independent on the overstory trees. Under pure F. sylvatica overstory the δ¹³C values of microbial biomarker PLFAs were slightly decreased (up to 2‰ for 17:0br) or unchanged after litter fall. By contrast, under both variants of mixed overstory the δ¹³C values of biomarker PLFAs of fungi (18:2ω6,9) were increased after litter fall (+3.5 and +3.8‰). This might be explained partly by a faster initial decomposition of foliar litter from mixed overstory already during litter fall as confirmed by higher CO₂ emission under mixed F. excelsior, Acer spp. and F. sylvatica than under pure F. sylvatica in this period. However, the involved microbial populations differed overstory-specific. Bacterial biomarker PLFAs with strongest overstory-specific differences in the response on litter fall were 17:0br (Gram-positive bacteria), 18:1 and 19:0cy (Gram-negative bacteria). The present results indicate that a tree species conversion even exclusively between deciduous tree species might alter the soil microbial C turnover during litter decomposition and suggest that it would in the long-term change the SOM stability and C storage.     

Economics of intercropping loblolly pine and switchgrass for bioenergy markets in the southeastern United States

The main objective of this study was to assess the economics of alley cropping of loblolly pine (Pinus taeda L.) and switchgrass (Panicum virgatum) in the southern United States. Assuming a price range of switchgrass between $15 and $50?Mg^?1 and yield of 12?Mg?ha^?1 year^?1, we investigated the effect of switchgrass production on the optimal forest management for loblolly pine stands under different stumpage prices. We considered the following potential scenarios: no competition between species for resources; reduced loblolly pine productivity due to competition with switchgrass; and reduced productivity of both species due to competition for nutrients, water and light. Findings also suggested that the optimal system would depend on the competitive interactions between switchgrass and loblolly pine crops, and the expected prices for each crop. Loblolly pine monoculture would be the most profitable option for landowners compared to intercropping systems with switchgrass below $30?Mg^?1. However, when switchgrass prices are ??$30?Mg^?1, landowners would be financially better off adopting intercropping if competitive interaction between crops were minimal. In order to realize higher economic returns for intercropping system, forest landowners must make some efforts in order to diminish the decline of productivity.     

Effect of multipurpose tree species on soil fertility and CO2 efflux under hilly ecosystems of Northeast India

A 26 years old agroforestry plantation consisting of four multipurpose tree species (MPTs) (Michelia oblonga Wall, Parkia roxburghii G. Don, Alnus nepalensis D. Don, and Pinus kesiya Royle ex-Gordon) maintained at ICAR Research Complex, Umiam, Meghalaya, India were compared with a control plot (without tree plantation) for soil fertility status and CO₂ efflux. The presence of trees improved all the physico-chemical and microbial biomass parameters studied in this experiment. Relative to control, soils under MPTs showed significant increases of 17 % soil organic carbon, 26 % available nitrogen (AN), 28 % phosphorus (AP), 50 % potassium (AK), 65 % mean weight diameter (MWD) of aggregates, 21 % moisture and 34 % soil microbial biomass carbon (MBC) while reducing the mean bulk density (7 %). However, these parameters significantly differed among the tree species i.e., soils under A. nepalensis and M. oblonga had higher values of these attributes except bulk density, than under other species. Irrespective of treatments, the values of all these attributes were higher in surface soils while bulk density was highest in subsurface (60–75 cm). Cumulative CO₂ efflux under MPTs was significantly higher (15 %) and ranged from 1.71 g 100 g^?1 (M. oblonga) to 2.01 g 100 g^?1 (A. nepalensis) compared to control at 150 days of incubation. In all the treatments, increment in temperature increased the oxidation of soil organic matter, thereby increased the cumulative CO₂ efflux from soils. Of the tree species, with increment in temperature, A. nepalensis recorded more CO₂ efflux (2.50 g 100 g^?1) than other MPTs but the per cent increase was more in control plot. P. kesiya and A. nepalensis recorded highest activation energy (59.1 and 39 kJ mol^?1, respectively). Net organic carbon sequestered in soil was highest under A. nepalensis (25.7 g kg^?1) followed by M. oblonga (19.3 g kg^?1), whereas control showed the lowest values. Amount of net carbon stored in the soil had significant and positive correlation with MBC (r = 0.706**), MWD (r = 0.636*), and AN (r = 0.825**).     

Early growth of Eucalyptus camaldulensis under agroforestry conditions at Mafiga,Morogoro, Tanzania

The growth of Eucalyptus camaldulensis clean weeded, spot weeded and intercropped with maize and beans was studied. At 4 m × 4 m and 5 m × 5 m spacings trees were significantly shorter after 15 months under a conventional spot weeding regime than with clean weeding or intercropping with beans. A satisfactory maize yield (683 kg ha^?1) was recorded from plots with trees spaced at 5 m × 5 m. Plots where trees were spaced at 4 m × 4 m and 3 m × 3 m gave significantly lower yields (444 kg ha^?1 and 283 kg ha^?1, respectively).     

Changes in soil microbial community and activity in warm temperate forests invaded by moso bamboo (<Emphasis Type="Italic">Phyllostachys pubescens</Emphasis>)

In the past few decades, moso bamboo (Phyllostachys pubescens) forests in Japan have rapidly expanded, and moso bamboo is now invading nearby native forests. In this study, we assessed the effects of moso bamboo invasion on the soil microbial community and activity in warm temperate forests in western Japan. We sampled soil, measured soil microbial respiration, and used phospholipid fatty acid (PLFA) analysis to examine changes in microbial community composition. We found that the invasion of bamboo into the native secondary forest of Japan can cause changes to some soil properties. We also observed a significant difference in soil microbial community composition between the bamboo and native forests. The ratio of bacterial PLFA to fungal PLFA was significantly higher after bamboo invasion, while bacterial PLFA contents were significantly lower in the organic layer. Soil microbial respiration rates significantly decreased in the organic layer, and significantly increased in the mineral layer. Microbial respiration activity, as indicated by soil microbial respiration rates per total PLFA content, decreased in the organic layer but increased in the mineral layer after bamboo invasion. These results indicate that bamboo invasion significantly affects associated soil microbial communities and decomposition patterns of soil organic matter.     

Microbial properties and litter and soil nutrients after two prescribed fires in developing savannas in an upland Missouri Ozark Forest

On some landscapes periodic fire may be necessary to develop and maintain oak-dominated savannas. We studied the effects of two annual prescribed burns to determine their effect on microbial activity and soil and litter nutrients 1 year after the last burn. Surface litter and soil from the upper 0–5 cm soil layer in three developing savannas (oak-hickory, Quercus-Carya), oak-hickory-pine (Quercus-Carya-Pinus), and pine (Pinus) were collected one year after the second of two annual prescribed burns. Surface litter was analyzed for nutrients and soil was analyzed for phospholipid fatty acids (PLFAs) and nutrients. Surface litter chemistry differed across the three savannas for potassium (K) and boron (B), being significantly (P < 0.05) higher for unburned forest than for burned forest. Among savannas, only sulfur (S) was higher for the pine savanna and B for the oak-hickory savanna, both were higher for unburned forest than for burned forest. For soil, calcium (Ca) and B differed across savannas, being higher for burned forest than for unburned forest. Among savannas, soil pH, Ca, and B concentrations were higher in soil from burned forest than from unburned forest. Total PLFA differed among savannas, but was not affected by burning treatments. However, the amounts of biomarkers for Gram-positive and Gram-negative bacteria were higher while the amount of biomarker for fungal PLFA was lower for burned forest than for unburned forest. Our results indicate that the two annual prescribed burns moderately affected PLFA microbial community structure and litter and soil nutrient concentrations. However, the long-term effects of fire on these study sites are not known and merit further study.     

Greenhouse biofumigation with <Emphasis Type="Italic">Melia azedarach</Emphasis> controls <Emphasis Type="Italic">Meloidogyne</Emphasis> spp. and enhances soil biological activity

The need for environmentally friendly agricultural practices has led to the development of plant-based nematicides for root-knot nematode control. The efficacy of these botanicals has been tested primarily under laboratory and rarely under actual field conditions. Moreover, any side effects on non-target soil organisms that support soil biological activity are usually ignored. Herein, we evaluate the efficacy of Melia azedarach preparations against Meloidogyne spp. in a tomato greenhouse, by root gall examination and soil J2 enumeration. We also assessed side effects on soil microbes through PLFA analysis and microbivorous nematodes, and we quantified several plant growth parameters (e.g., fruit number and weight, root weight). Different treatments within the greenhouse included M. azedarach ripe fruit powder (MFP), ripe fruit water extract (MWE) and furfural, one of the principal active ingredients of M. azedarach and previously known to exhibit fumigant nematicidal activity. Results were compared to those obtained with the commercial nematicide oxamyl (Vydate^® 10 SL) and an untreated control. All treatments were repeated every 20 days throughout the cultivation period. MFP and MWE suppressed Meloidogyne spp. often at the same levels obtained by furfural and oxamyl treatments and enhanced soil biological activity, as indicated by the proliferation of soil microbes and microbial feeding nematodes. Furfural and oxamyl adversely affected the soil community, especially the free-living nematodes. Moreover, furfural was phytotoxic to tomato plants in spite of its natural origin.     

长期粗放经营毛竹林土壤微生物群落演变特征

[目的]通过分析土壤微生物生物量及群落结构的演变趋势,筛选影响土壤微生物群落的关键环境因子,揭示土壤微生物群落对毛竹林长期粗放经营的响应机理。[方法]选取不同粗放经营年限(5 a、9 a、15 a、18 a)毛竹林,以天然马尾松林(Masson pine,MP)作为对照,采用磷脂脂肪酸(Phospholipid fatty acids,PLFA)分析方法表征土壤微生物量及群落结构。[结果]结果表明,毛竹林土壤微生物总PLFA含量以及细菌、真菌、放线菌等PLFA含量均显著低于马尾松林(P0.05),但不同经营年限毛竹林之间没有显著差异。土壤碱解氮及有效磷含量对土壤微生物总PLFA含量以及细菌、真菌、原生动物等PLFA含量影响显著(P0.05),而土壤碱解氮、p H值以及有机质含量对放线菌PLFA含量影响显著(P0.05)。长期粗放经营过程中毛竹林土壤微生物丰富度及多样性均呈逐渐下降趋势。非度量多维尺度转换排序(Non-metric multidimensional scaling,NMDS)分析结果表明,毛竹林土壤微生物群落结构与马尾松林有明显区分(R=0.388 1,P=0.009)。土壤含水量、碱解氮、有效磷以及p H值合计解释了90.28%的微生物群落结构变异量,其中土壤含水量、碱解氮、有效磷贡献显著(P0.05)。[结论]长期粗放经营降低了毛竹林土壤微生物量,改变了群落结构,其生态风险还有待于进一步评估。     

Potential contribution of Leucaena hedgerows intercropped with maize to the production of organic nitrogen and fuelwood in the lowland tropics

Available information is applied to formulate quantitative hypotheses on the impact of intercropping Leucaena hedgerows with maize upon the physical productivity of grain and fuelwood. Data would indicate that productivity of organic nitrogen (N) by Leucaena hedgerows cut approximately every 8 weeks at a height of 15–30 cm and planted at a distance between rows wider than 150 cm is 45 g m^?1 yr^?1. When soil-N availability is the limiting factor, utilization of Leucaena-N by the maize crop appears to be negatively related to baseline maize production. The grain: Leucaena-N ratio declines from 20:1, when maize productivity is in the order of 500 kg ha^?1, to 3:1, when the 4000 kg level is achieved. Hedgerow N productivity, N utilization by the maize crop, and proportion of land planted to maize were used to derive yield estimates per area of intercropped land under different intercropping arrangement. It seems that the impact of hedge intercropping on maize productivity, although substantial, would be limited to systems where existing production levels of maize are lower than 1500 kg ha^?1. As expected, production per hectare decreases as spacing between Leucaena hedgerows increases. For a 1000 kg ha^?1 baseline, hypothetical increments expressed as percentage of baseline production range from 112% to 28% for between-hedgerow spacings of 1.5 and 6 m respectively. Information analyzed would indicate apotential for Leucaena hedgerow intercropping to increase maize productivity. Research required to substantiate the formulated hypotheses is discussed.     

Earthworm population and microbial activity temporal dynamics in a Caspian Hyrcanian mixed forest

Few studies have analyzed how tree species within a mixed natural forest affect the dynamics of soil chemical properties and soil biological activity. This study examines seasonal changes in earthworm populations and microbial respiration under several forest species (Carpinus betulus, Ulmus minor, Pterocarya fraxinifolia, Alnus glutinosa, Populus caspica and Quercus castaneifolia) in a temperate mixed forest situated in northern Iran. Soil samplings were taken under six individual tree species (n = 5) in April, June, August and October (a total of 30 trees each month) to examine seasonal variability in soil chemical properties and soil biological activity. Earthworm density/biomass varied seasonally but not significantly between tree species. Maximum values were found in spring (10.04 m^?2/16.06 mg m^?2) and autumn (9.7 m^?2/16.98 mg m^?2) and minimum in the summer (0.43 m^?2/1.26 mg m^?2). Soil microbial respiration did not differ between tree species and showed similar temporal trends in all soils under different tree species. In contrast to earthworm activity, maximum microbial activity was measured in summer (0.44 mg CO₂–C g soil^?1 day^?1) and minimum in winter (0.24 mg CO₂–C g soil^?1 day^?1). This study shows that although tree species affected soil chemical properties (pH, organic C, total N content of mineral soils), earthworm density/biomass and microbial respiration are not affected by tree species but are controlled by tree activity and climate with strong seasonal dynamics in this temperate forest.     

Comparative field performance of some agricultural crops under a canopy of Populus deltoides and Ulmus wallichiana

The performance of maize, beans and sunflower was evalu-ated under a canopy of Populus deltoides and Ulmus wallichiana at Fac-ulty of Agriculture, Wadura. The germination, growth and yield of the three...     

The effects of phenolic acid on nitrogen metabolism in <Emphasis Type="Italic">Populus</Emphasis> × <Emphasis Type="Italic">euramericana</Emphasis> ‘Neva’

The declines in soil fertility and productivity in continuously cropped poplar plantations are related to phenolic acid accumulation in the soil. Nitrogen is a vital life element for poplar and whether the accumulation of phenolic acid could influence nitrogen metabolism in poplar and thereby hinder continuous cropping is not clear. In this study, poplar cuttings of Populus × euramericana ‘Neva’ were potted in vermiculite, and phenolic acids at three concentrations (0X, 0.5X and 1.0X) were added according to the actual content (1.0X) in the soil of a second-generation poplar plantation. Each treatment had eight replicates. We measured gas exchange parameters and the activities of key enzymes related to nitrogen metabolism in the leaves. Leaf photosynthetic parameters varied with the concentration of phenolic acids. The net photosynthetic rate (P_N) significantly decreased with increasing phenolic acid concentration, and non-stomatal factors might have been the primary limitation for P_N. The activities of nitrate reductase (NR), glutamine synthetase (GS) and glutamate synthase (GOGAT), as well as the contents of nitrate nitrogen, ammonium nitrogen, and total nitrogen in the leaves decreased with increasing phenolic acid concentration. This was significantly and positively related to P_N (P < 0.05). The low concentration of phenolic acids mainly affected the transformation process of NO₃^? to NO₂^?, while the high concentration of phenolic acids affected both processes, where NO₃^? was transferred to NO₂^? and NH₄⁺ was transferred to glutamine (Gln). Overall, phenolic acid had significant inhibitory effects on the photosynthetic productivity of Populus × euramericana ‘Neva’. This was probably due to its influence on the activities of nitrogen assimilation enzymes, which reduced the amount of amino acids that were translated into protein and enzymes. Improving the absorption and utilization of nitrogen by plants could help to overcome the problems caused by continuous cropping.     

Nitrogen application and intercropping change microbial community diversity and physicochemical characteristics in mulberry and alfalfa rhizosphere soil

Intercropping of mulberry(Morus alba L.)and alfalfa(Medicago sativa L.) is a new forestry-grass compound model in China,which can provide high forage yields with high protein.Nitrogen application is one of the important factors determining the production and quality of this system.To elucidate the advantages of intercropping and nitrogen application,we analyzed the changes of physicochemical properties,enzyme activities,and microbial communities in the rhizosphere soil.We used principal components analysis(PCA) and redundancy discriminators analysis to clarify the relationships among treatments and between treatments and environmental factors,respectively.The results showed that nitrogen application significantly increased pH value,available nitrogen content,soil water content(SWC),and urea(URE) activity in rhizosphere soil of monoculture mulberry.In contrast,intercropping and intercropping+N significantly decreased pH and SWC in mulberry treatments.Nitrogen,intercropping and intercropping+N sharply reduced soil organic matter content and SWC in alfalfa treatments.Nitrogen,intercropping,and intercropping+N increased the values of McIntosh diversity(U),Simpson diversity(D),and Shannon-Weaver diversity(H') in mulberry treatments.However,PC A scatter plots showed clustering of monoculture mulberry with nitrogen(MNE) and intercropping mulberry without nitrogen(M0).Intercropping reduced both H' and D but nitrogen application showed no effect on diversity of microbial communities in alfalfa.There were obvious differences in using the six types of carbon sources between mulberry and alfalfa treatments.Nitrogen and intercropping increased the numbers of sole carbon substrate in mulberry treatments where the relative use rate exceeded 4%.While the numbers declined in alfalfa with nitrogen and intercropping.RDA indicated that URE was positive when intercropping mulberry was treated with nitrogen,but was negative in monoculture alfalfa treated with nitrogen.Soil pH and SWC were positive with mulberry treatments but were negative with alfalfa treatments.Intercropping with alfalfa benefited mulberry in the absence of nitrogen application.Intercropping with alfalfa and nitrogen application could improve the microbial community function and diversity in rhizosphere soil of mulberry.The microbial community in rhizosphere soil of mulberry and alfalfa is strategically complementary in terms of using carbon sources.     

Influence of direction and distance from trees on wheat yield and photosynthetic photon flux density (Qp) in a Paulownia and wheat intercropping system

A Paulownia-winter wheat intercropping experiment with the object of quantifying photosynthetically active radiation (PAR) and its effect on wheat yield was conducted 60 km south of Zhengzhou (35°N 113°E), Henan Province, PR China, from September 1991 to July 1992 using a tree and crop interface approach. The middle row of three 240 m long rows of 11-year-old trees was studied for its effects on the yield of irrigated and fertilized winter wheat. Photosynthetic photon flux density (Q_p) was quantified using a split-plot design with four blocks. There were four distance (subplot) treatments (2.5 m, 5 m, 10 m and 20 m) and two direction (main plot) treatments laid out to the east and west of a north-south tree line. Results showed no difference in direction effects but Q_p did affect total grain weight (P = 0.0047) between 2.5 m and 20 m. A regression equation was fit using the mean for each distance treatment: Y = 391.7 + 4.57X with r² = 0.9310 indicating a yield increase of 4.57 g m⁻² (45.7 kg ha⁻¹) over a distance of 2.5 m to 20 m from the trees.