辽西北沙地苹果-花生间作系统土壤养分空间分布特征及间作效应

[目的] 研究辽西北沙地农林复合系统土壤养分的空间分布及其效应,从土壤养分角度探讨果农间作系统中果树和农作物对土壤养分的相互作用关系,为该区农林复合系统的可持续经营提供科学合理的依据。[方法] 以苹果与花生间作、花生单作、苹果单作为研究对象,对0-60 cm土层深度,0-300 cm水平距离范围内土壤养分含量进行测定和分析。[结果] 沙地间作系统中土壤有机质、速效钾极缺乏,全氮、碱解氮很缺乏,全磷缺乏,有效磷含量中等;间作系统在水平方向上,苹果树和花生植株对总养分有机质、氮、磷的竞争激烈位点位于果树带区,对有效养分氮、磷、钾的竞争激烈位点位于近果树作物区;在垂直方向上,各养分总体表现出了表聚性,间作系统对有机质、有效磷的竞争主要位于深土层,对全磷、速效钾的竞争主要位于表土层,对全氮、碱解氮表现为合作效应,表土层效应更高;与苹果单作、花生单作相比较,间作系统速效钾和有效磷含量呈现负效应。[结论] 沙地苹果-花生间作系统土壤养分贫瘠,应在果树带区施用有机肥、磷肥,作物区施入钾肥,以减轻养分竞争,提高养分效应。     

Nutrient and water uptake by roots of forest trees

Although per growing season nutrient uptake of adequately growing forest trees is less than the nutrient uptake of annual crop species, nutrient uptake per unit root length in trees is considerable. Because of high heterogeneity of soil conditions and root growth in forest soils, modelling of uptake processes is even more difficult for forest than for crop stands. Detailed studies show that white lips of growing tree roots have a high nutrient uptake capacity. However, most root tips are usually colonised by mycorrhizal fungi. These fungi can participate substantially in tree nutrient uptake, in particular in the utilisation of organically-bound phosphorus and nitrogen in soils. Mycorrhizal hyphae, root tips, and older root zones can all absorb water, but their actual contribution is difficult to assess. In this review, experimental results from our laboratory and literature data are used to describe the potential activity of tree roots and mycorrhizas in nutrient and water uptake. Methodology for in situ measurements must be developed to quantify at different forest sites the actual contribution of mycorrhizas and different root parts.     

间作及农林复合系统中植物组分间养分竞争机理分析

农林复合系统、间作及套作中植物组分之间养分竞争普遍存在。植物的养分竞争主要包括种内竞争和种间竞争。光照、温度、水分、土壤、微生物。低等动物等外界因素对植物的竞争作用具有明显的影响。农林复合系统中,林种和林间作物品种的选用、林的修剪和管理方式等技术的应用可调控组分间的竞争作用。     

Transition from Forest‐based to Cereal‐based Agricultural Systems: A Review of the Drivers of Land use Change and Degradation in Southwest Ethiopia

The southwestern Ethiopian montane forests are one of the most species‐rich ecosystems and are recognised globally as a priority area for the conservation of biodiversity. Particularly, in contrast to the drier central and northern Ethiopian highlands, they have received little attention by researchers. Here, we review changes to agricultural systems in and around these forests that are known as the genetic home of coffee (Coffea arabica L.) and that are important to the livelihoods of many rural people who have developed traditional management practices based on agro‐ecological knowledge, religious taboos and customary tenure rights. We explored the impacts of conversions to agroforestry and cereal‐based cropping systems on biodiversity, soil fertility, soil loss and the socio‐economic conditions and culture. The increasing trend of cereal cropping, resettlement and commercial agriculture causes the deterioration of natural forest cover in the region and threatens biodiversity, land quality, sustainable, traditional farming practices and the livelihood of the local community. Large‐scale plantations of tea, coffee, soapberry locally known as endod (Phytolacca dodecandra L'Hér.) and cereals have resulted in biodiversity loss. Following the conversion of forests, cultivated fields exhibit a significant decline in soil fertility and an increase in soil loss as compared with the traditional agroforestry system. The establishment of a sustainable agricultural system will require a change in paradigm, whereby the intrinsic values of the traditional forest‐based agricultural system are recognised, rather than the ongoing mimicking of agricultural policies that were developed for the open fields of central Ethiopia. Copyright © 2016 John Wiley & Sons, Ltd.     

Soil quality assessments in integrated crop–livestock–forest systems: A review

Integrated crop–livestock–forest is a promising strategy to improve soil quality. It comprises four different integrated farming systems: crop–livestock, crop–forest, forest–livestock and crop–livestock–forest. This work systematically reviewed studies about integrated crop–livestock–forest systems and soil quality. A total of 92 papers were retrieved from the Web of Science—Clarivate Analytics platform, and the following information was analysed: publication year, institution, region of the studied site, type of integrated system, soil type, tillage system, maximum soil depth and the soil quality indicators assessed. Most studies were published in the second half of the 2010s. Brazil is a prominent focus of research about soil quality and integrated crop–livestock–forest systems, with significant contribution from its central and southern regions. The Embrapa was the main publishing institution, present in over one‐third of the studies. Crop–livestock was the most common integrated system, Ferralsols was the most common soil group, and most of the studied soils were clayey. No tillage was the main tillage system. Most studies focused on the topsoil, assessing physical and/or chemical soil quality indicators. More emphasis on biological indicators of soil quality is required, as well as assessments integrating biological, physical and chemical indicators of soil quality. Future works should compare different integrated systems, including assessments deeper in the soil profile, especially in systems with the forest component, and also in sandy and silty soils. Soil quality indicators that have been rarely used should be further tested. Novel indicators should be added to better understand the promotion of soil quality by integrated crop–livestock–forest systems.     

Conversion of a tropical forest into agroforest alters the fine root-related carbon flux to the soil

Large areas of remaining tropical forests are affected by anthropogenic disturbances of various intensities. These disturbances alter the structure of the forest ecosystem and consequently its carbon budget. We analysed the role of fine root dynamics in the soil carbon budget of tropical moist forests in South-east Asia along a gradient of increasing disturbance intensity. Fine root production, fine root turnover, and the associated carbon fluxes from the fine root system to the soil were estimated with three different approaches in five stands ranging from an old growth forest with negligible anthropogenic disturbance to a cacao agroforestry system with planted shade trees. Annual fine root production and mortality in three natural forest sites with increasing canopy openness decreased continuously with increasing forest disturbance, with a reduction of more than 45% between the undisturbed forest and the forest with large timber extraction. Cacao agroforestry stands had higher fine root production and mortality rates than forest with large timber extraction but less than undisturbed forest. The amount of carbon annually transferred to the soil carbon pool through fine root mortality was highest in the undisturbed forest and generally decreased with increasing forest use intensity. However, root-related C flux was also relatively high in the plantation with planted shading trees. In contrast, the relative importance of C transfer from root death in the total above- and below-ground C input to the soil increased with increasing forest use intensity and was even similar to the C input via leaf litter fall in the more intensively managed agroforest. We conclude that moderate to heavy disturbance in South-east Asian tropical moist forests has a profound impact on fine root turnover and the related carbon transfer to the soil.     

Growth and phosphorus uptake of maize cultivated alone,in mixed culture with other crops or after incorporation of their residues

Intercropping or rotating of P‐efficient crop species which mobilize sparingly soluble P by their root exudates can have beneficial effects on growth and P uptake of P‐inefficient species. We aimed at studying the effect of intercropping or incorporating of crop residues of P‐efficient crops on the components of maize P‐uptake, i.e. the root‐system size and P influx (P‐uptake rate per unit root length). This was studied in 3 pot experiments in a low‐P sandy soil. In the first experiment, maize was intercropped with white lupine, sugar beet or oilseed rape, and with groundnut in the second experiment. In the third experiment, maize was grown after incorporating the crop residues of white lupine, sugar beet or oilseed rape. Maize growth and yield was strongly inhibited when intercropped with white lupine, sugar beet or oilseed rape, probably because of competition for nutrients. But with groundnut as the accompanying species, maize yield was increased by a factor of 3, mainly because of an enhanced P influx. Crop residues of oilseed rape and sugar beet increased the yield of maize by factors 2 and 1.6, respectively, because of a 3 and 2 times higher P uptake as compared to maize grown after maize without incorporation of crop residue. The reason for the higher maize P‐uptake after oilseed rape was an 11 times higher P influx as compared to maize without crop residues, and after sugar beet residues because of an enhanced root growth and a 4 times higher P influx. Lupine residues did not improve maize growth, mainly because of a low P influx, which was even less than that of maize grown without crop residues. The soil solution P concentration and calcium acetate lactate‐extractable P (CAL P) measured in this study did not reflect the P availability as indicated by the plants (P uptake, P influx). This indicates that other mechanisms such as P mobilization in the rhizosphere by root exudates or cell‐wall components were responsible for the increased P availability. These mechanisms need further investigation.     

Agroforestry as a strategy for carbon sequestration

During the past three decades, agroforestry has become recognized the world over as an integrated approach to sustainable land use because of its production and environmental benefits. Its recent recognition as a greenhouse gas–mitigation strategy under the Kyoto Protocol has earned it added attention as a strategy for biological carbon (C) sequestration. The perceived potential is based on the premise that the greater efficiency of integrated systems in resource (nutrients, light, and water) capture and utilization than single‐species systems will result in greater net C sequestration. Available estimates of C‐sequestration potential of agroforestry systems are derived by combining information on the aboveground, time‐averaged C stocks and the soil C values; but they are generally not rigorous. Methodological difficulties in estimating C stock of biomass and the extent of soil C storage under varying conditions are compounded by the lack of reliable estimates of area under agroforestry. We estimate that the area currently under agroforestry worldwide is 1,023 million ha. Additionally, substantial extent of areas of unproductive crop, grass, and forest lands as well as degraded lands could be brought under agroforestry. The extent of C sequestered in any agroforestry system will depend on a number of site‐specific biological, climatic, soil, and management factors. Furthermore, the profitability of C‐sequestration projects will depend on the price of C in the international market, additional income from the sale of products such as timber, and the cost related to C monitoring. Our knowledge on these issues is unfortunately rudimentary. Until such difficulties are surmounted, the low‐cost environmental benefit of agroforestry will continue to be underappreciated and underexploited.     

The influence of American Chestnut (Castanea dentata) on nitrogen availability, organic matter and chemistry of silty and sandy loam soils

American chestnut trees once dominated vast areas of deciduous forest in eastern North America, but the exotic chestnut blight almost eliminated the species from the region. Introduction of blight-resistant American chestnut hybrids will probably start in the next decade after many years of tree breeding. What were the historic effects of chestnut on forest soils, and what changes may follow reintroduction of hybrid chestnuts? A site in southern Wisconsin provided an opportunity to examine the effect of chestnut trees on soil properties. At this site, 600 km northwest of chestnut's historic distribution, naturalized chestnuts have spread throughout an intact mixed-species forest from nine planted trees. The site contains soil developed on a silty loess-mantled ridge that abuts sandier hillslopes, allowing the effects of individual chestnuts to be examined on two soil types. I sampled and analyzed forest floor and mineral soils beneath canopies of individual American chestnuts and the surrounding mixed-species deciduous forest on fine-silt and sandy-loam soil types. On sandy loam soils, total soil carbon (C) and nitrogen (N), inorganic N and net mineralization and nitrification rates were 10–17% higher beneath chestnut canopies compared to soils beneath mixed-species deciduous forest. The pool of total soil N beneath chestnut canopies was positively related to the silt content of the sandy loam soils. In contrast, there were no differences between properties of chestnut canopy and mixed-species deciduous forest soils on the fine silt texture class. On sandy loam soil conditions common throughout the pre-blight distribution of American chestnut, soil biogeochemical processes differ beneath individual chestnut trees relative to a diverse mixture of deciduous species. These findings suggest that widespread chestnut reintroduction has the potential to alter both stand- and watershed-scale processes.     

残落物混合分解对杨树-农作物复合系统土壤碳氮矿化的影响

采用室内培养的方法研究杨-麦、杨-花生等不同复合经营模式下,杨树叶与农作物秸秆混合后对土壤碳、氮矿化及土壤微生物量的影响。结果表明:(1)单一模式中,花生叶处理的有机碳矿化累积量最大,花生茎秆、杨树叶处理次之,小麦秸秆处理最低。混合处理有机碳矿化累积量依次为杨树叶-花生叶>杨树叶-花生茎秆>杨树叶-小麦秸秆,且培养结束时,混合物表现出明显的促进作用;(2)土壤微生物量碳、氮与各残落物氮含量、C/N比存在显著的相关性;(3)杨树叶、小麦秸秆及其混合物处理的土壤矿质态氮含量均低于对照,而添加花生叶、花生茎秆以及它们与杨树叶的混合物使矿质态氮含量高于对照。试验说明杨-麦、杨-花生复合模式均能有效提高土壤微生物的生物量,调节碳的动态及氮的供应,而选择种植含氮量高的农作物更有利于促进残落物分解和养分归还,这对深入研究林-农复合系统的模式筛选、结构优化及可持续经营具有一定的现实意义。     

Degradation and restoration of sandy soils under different agricultural land uses in northeast Thailand: a review

Conversion of natural forest to agricultural land use has significantly lowered the soil organic matter (SOM) content in sandy soils of northeast Thailand. This paper reviews the findings of comparative studies on contents of SOM pools (labile, i.e. microbial biomass and particulate organic matter—POM and stable, i.e. humic substance) and related soil aggregate formation, in natural forest plots and cultivated fields (monocrops of cassava, sugarcane and rice) in sites representative of northeast Thailand from the viewpoints of terrain (i.e. undulating), soils (sandy) and land use and discusses the restoration of SOM and fertility (nitrogen) in these degraded soils. Monocultural agriculture brings about the degradation of all SOM pools and associated soil aggregation as compared to the forest system because of decreased organic inputs and more frequent soil disturbance. The build‐up of SOM was achieved through the continuous recycling of organic residues produced within the system. Low‐quality residues contributed the largest SOM build‐up in whole and fractionated SOM pools, including POM and humic substance. However, to restore N fertility, high quality residues, (i.e. with low C/N ratios, lignin and polyphenols) were also needed. Timing of N release to meet crop demand was achieved by employing a mixture of high and low quality residues. Selection of appropriate residues for N sources was affected by environmental factors, notably soil moisture regimes, which differed in upland field and lowland paddy subsystems. Copyright © 2007 John Wiley & Sons, Ltd.     

Spatial patterns of nitrogen mineralization, fertilizer distribution and roots explain nitrate leaching from mature Amazonian oil palm plantation

Abstract. The African oil palm ( Elaeis guineensis ) is relatively well adapted to the pedoclimatic conditions of central Amazonia. The clayey upland soils of the region are well supplied with nitrogen, although they are deficient in most other nutrients. Under these conditions, oil palm does not respond to N fertilization with yield increases. In this research, the N status of a central Amazonian upland soil was evaluated after having supported a productive oil palm plantation for 15 years without N fertilization. Mineral N in the upper 2 m of soil showed pronounced spatial patterns, with very low concentrations close to the palms, indicative of efficient N uptake by the palms, and evidence for nitrate leaching into the subsoil in the inter-tree spaces despite the near-absence of a leguminous cover crop during the previous ten years. The pronounced increases of mineral N with increasing tree distance were explained by increases in N mineralization and a strong decrease in fine root length density of the palms, especially in the subsoil. Failure of the palms to fully occupy the available soil volume with their roots was apparently related to fertilizer placement close to the stem base, which over the years had led to steep fertility gradients between the soil under the trees and the inter-tree spaces. Broadcast fertilization would have presumably favoured a more extensive lateral root development of the palms, and consequently improved nutrient and water uptake from the inter-tree spaces. The incomplete soil occupation by the palm roots also suggests that young oil palms can be associated with shade tolerant crops without much risk of root competition. These conclusions may be valid also for other tree crops and may help to reduce nitrate leaching and consequently the need for N fertilization in Amazonian tree crop agriculture.     

Productivity enhancement of salt‐affected environments through crop diversification

Recent trends and future demographic projections suggest that the need to produce more food and fibre will necessitate effective utilization of salt‐affected land and saline water resources. Currently at least 20 per cent of the world's irrigated land is salt affected and/or irrigated with waters containing elevated levels of salts. Several major irrigation schemes have suffered from the problems of salinity and sodicity, reducing their agricultural productivity and sustainability. Productivity enhancement of salt‐affected land and saline water resources through crop‐based management has the potential to transform them from environmental burdens into economic opportunities. Research efforts have led to the identification of a number of field crops, forage grasses and shrubs, aromatic and medicinal species, bio‐fuel crops, and fruit tree and agroforestry systems, which are profitable and suit a variety of salt‐affected environments. Several of these species have agricultural significance in terms of their local utilization on the farm. Therefore, crop diversification systems based on salt‐tolerant plant species are likely to be the key to future agricultural and economic growth in regions where salt‐affected soils exist, saline drainage waters are generated, and/or saline aquifers are pumped for irrigation. However, such systems will need to consider three issues: improving the productivity per unit of salt‐affected land and saline water resources, protecting the environment and involving farmers in the most suitable and sustainable crop diversifying systems to mitigate any perceived risks. This review covers different aspects of salt‐affected land and saline water resources, synthesizes research knowledge on salinity/sodicity tolerances in different plant species, and highlights promising examples of crop diversification and management to improve and maximize benefits from these resources. Copyright © 2008 John Wiley & Sons, Ltd.     

Characterizing organic matter of soil aggregate coatings and biopores by Fourier transform infrared spectroscopy

In some soils, aggregate coatings and walls of biopores differ in the content of clay and organic carbon from that of the aggregate interiors or the soil matrix. The composition of the organic matter on aggregates and on the surfaces of biopores is largely unknown. We have compared the composition of organic matter between inner and outer parts of aggregates and between biopore walls and the soil matrix in a loamy arable soil and a sandy forest one. Hot‐water‐ and sodium‐pyrophosphate‐extractable organic matter was analysed by Fourier transform infrared (FT‐IR) spectroscopy. For the sandy forest soil, the FT‐IR spectra showed that organic matter from the walls of root channels contains fewer functional groups with absorption bands at 1740–1710 cm^?1 and 1640–1600 cm^?1 than that from burrow fillings. For the arable soil, the content of these functional groups in hot‐water‐soluble organic matter from the coatings is less than in that from the interiors in the topsoil, and the reverse is so in the subsoil, probably because water‐soluble organic matter containing these functional groups has moved from topsoil to subsoil. The results indicate that root channels in the forest soil have more reactive zones in an otherwise relatively inert sandy matrix, whereas aggregate coatings in the arable subsoil have a greater cation exchange capacity and a greater sorption potential for hydrophobic substances than the aggregate interiors.     

Mechanisms of potassium uptake efficiency and dynamics in the rhizosphere of safflower and sunflower in different soils

Potassium uptake efficiency of safflower and sunflower was studied under semi-controlled conditions in loamy and sandy soils. Both species performed better in loamy soil. Safflower had higher agronomic efficiency and higher relative root length under suboptimal K supply. Safflower had higher specific root density and less root radius at all K levels. Safflower had higher relative root-shoot ratio under suboptimal K in loamy soil. Both species had similar K-influx at low and optimal K in loamy soil, while sunflower had higher influx under suboptimal and optimal supplies in sandy soil. Safflower had higher shoot demand in both soils under suboptimal and optimal K. Both species depleted similar amounts of soil solution-K under suboptimal K in sandy soil, while sunflower was more efficient under suboptimal levels in loamy soils. Sunflower depleted more extractable-K under both suboptimal and optimal K. Safflower could be considered K-uptake efficient crop.     

Physical resilience of soil to field compaction and the interactions with plant growth and microbial community structure

Soil compaction has deleterious effects on soil physical properties, which can affect plant growth, but some soils are inherently resilient, whereby they may recover following removal of the stress. We explored aspects of soil physical resilience in a field‐based experiment. We subjected three soils of different texture, sown with winter wheat or remaining fallow, to a compaction event. We then monitored soil strength, as a key soil physical property, over the following 16 months. We were also interested in the associated interactions with crop growth and the microbial community. Compaction had a considerable and sustained effect in a sandy loam and a sandy clay loam soil, resulting in an increase in strength and decreased crop yields. By contrast compaction had little effect on a clay soil, perhaps due initially to the buoyancy effect of pore water pressure. Fallow clay soil did have a legacy of the compaction event at depth, however, suggesting that it was the actions of the crop, and rooting in particular, that maintained smaller strengths in the cropped clay soil rather than other physical processes. Compaction generally did not affect microbial communities, presumably because they occupy pores smaller than those affected by compaction. That the clay soil was able to supply the growing crop with sufficient water whilst remaining weak enough for root penetration was a key finding. The clay soil was therefore deemed to be much more resilient to the compaction stress than the sandy loam and sandy clay loam soils.     

Evaluation of Dolomite Phosphate Rock–N‐Viro Soil Mixtures for Growth of a Horticultural Crop in an Acidic Sandy Soil

Abstract

Most agricultural soils in the Indian River area, South Florida, are sandy with minimal holding capacity for moisture and nutrients. Phosphorus (P) leaching from these soils has been suspected of contributing to the eutrophication of surface waters in this region. Dolomite phosphate rock (DPR) and N‐viro soil are promising amendments to increase crop production and reduce P loss from sandy soils. Soil incubation and greenhouse pot experiments were conducted to examine the effects of Florida DPR–N‐viro soil mixtures on the growth of a horticultural crop in an acidic sandy soil and to generate information for developing a desired formula of soil amendments. Dolomite phosphate rock and N–viro soil application increased soil pH, electrical conductivity (EC), extractable P, calcium (Ca), and magnesium (Mg). N–viro soil had greater effect on soil pH, organic matter content, and microbial biomass than the DPR. Comparatively higher nitrification rates were found in the N–viro soil treatment than the DPR treatment. A systematic decrease in soil‐extractable P was found with increasing proportions of N‐viro soil from the combined amendments. Greenhouse study demonstrated that the application of DPR and N‐viro soil significantly improved dry‐matter yield and increased plant P, Ca, and Mg concentrations of radish (Raphanus sativus L.). Based on dry‐matter yield and plant N uptake, the combined amendments that contained 30% or 20% of DPR materials appear to be optimal but remain to be confirmed by field trials.     

黄土高原林农复合生态系统建造模式及效益的研究

当今林农复合生态系统的研究已受到许多国家的重视。本文提出发展能源林,解决黄土高原农村能源问题,可实行林农牧相结合的技术方针,即建立以沙棘、山桃、柠条、刺槐等能源林树种为主居于上层空间,在下层以带状或行间配置粮、油作物或牧草等,组成林农复合生态系统的建造模式,以提高能源林的生物产量、经济效益以及土地利用率。     

Pedologic and geomorphic impacts of a tornado blowdown event in a mixed pine-hardwood forest

Biomechanical effects of trees on soils and surface processes may be extensive in forest environments. Two blowdown sites caused by a November 2005 tornado in the Ouachita National Forest, Arkansas allowed a case study examination of bioturbation associated with a specific forest blowdown event, as well as detailed examination of relationships between tree root systems, soils, and underlying bedrock. The sites occur within mixed shortleaf pine and hardwood forests. More than 95% of trees in the severe blowdown areas were either uprooted or suffered trunk break, with uprooting more common than breakage. Within the most heavily damaged areas all uprooted trees were pines, while all trees left standing were hardwoods. Root wads of uprooted trees had a mean surface area of about 3 m² and volume of about 2 m³, though individual sizes were quite variable. Nearly 4% of the ground surface area was affected by uprootings, with a soil volume equivalent to a disturbance of the entire surface area to a depth of 2.4 cm. Tree size (as measured by diameter at breast height) was significantly related to the area and volume of root wads (R² = 0.55, 0.71, respectively), with volume of uprooted soil varying as diameter to the ~ 3 power, suggesting that the timing of blowdown events relative to tree age or growth stage significantly influences the area of disturbance and the mass and volume of material involved. In 93% of cases the roots of the uprooted trees contacted or penetrated the underlying bedrock, and in all those cases bedrock was quarried by uprooting. Only 11% of the tree throws showed evidence of general lateral root turning at the soil–bedrock interface; in most cases roots penetrated bedrock along joints. The propensity for tree roots to penetrate bedrock joints, facilitate weathering, and excavate bedrock during uprooting supports the idea that tree roots play a predominant role in locally deepening soils.