Can agroforestry improve soil fertility and carbon storage in smallholder banana farming systems?

Soil fertility depletion is a major constraint to agricultural production for smallholder farming households in many sub‐Saharan countries, and it is worsened by climate variability. In order to sustain food security for a growing population, measures have to be taken against C and nutrient losses from soils. This study examines whether banana–coffee agroforestry systems can improve soil fertility and C pools in smallholder farms in E Africa amidst observed climate variability. We selected 20 farms in Central Uganda, where soil samples were obtained from the top and subsoil layers. Samples were analyzed for several soil fertility parameters including soil organic matter (SOM), total soil organic C, pH, total N, plant‐available P, exchangeable K, texture, and bulk density. Soil C stocks were calculated based on soil organic C concentrations and bulky density. We measured tree diameter and height and calculated aboveground plant biomass using allometric equations. Belowground biomass was estimated using equations based on the respective aboveground plant biomass. Our results show that banana–coffee agroforestry farming systems had significantly higher total SOM and total N compared to the banana monoculture. Similar trends were observed for soil C stocks and total C pools. The former contained 1.5 times higher soil C stocks than the latter. Likewise, the mean total C pools for the banana–coffee agroforestry farm plots were 26% larger than that under banana monoculture. However, exchangeable K was higher in the soil of banana monocultures. Plant‐available P levels were limiting under both farming systems. The study demonstrates that beyond socio‐economic benefits banana–coffee agroforestry farming systems have beneficial effects on soil fertility and C sequestration compared to banana monocultures in the study area. However, precautions to avoid P depletion have to be taken under current climate conditions.     

Biodiversity and Ecosystem Functional Enhancement by Forest Restoration: A Meta‐analysis in China

Large‐scale forest loss and degradation have dire consequences for biodiversity maintenance and provision of vital ecosystem services. Despite recent increasing efforts for forest restoration and sustainable management, there have been no comparative studies of biological taxonomy and multiple ecosystem functions to assess the effectiveness of forest restoration programmes, and how they vary through space and time. Here, we provided a quantitative assessment of the recovery of biodiversity and ecosystem functions by forest restoration in China using a meta‐analysis of 172 studies. We found that biodiversity and ecosystem functions were substantially increased in restored forests comparing with the degraded states. However, these restoration effects varied considerably by degradation origin, restoration approach, restoration age, ecological domains, taxonomic group and ecosystem function that is measured. Results also revealed that forest restoration from degraded states could not lead to full recovery of biodiversity and ecosystem functions, highlighting the irreplaceability of primary forests. We advocate allowing for natural or passive recovery, especially where biophysical conditions are favourable for spontaneous succession, or too harsh for human‐aided restoration, and choosing a combination of passive and active restoration measures based on adaptive management strategies. Our meta‐analysis provided fundamental insights into bridging the gap between small‐scale experiments and broad‐scale management needs towards highly effective and sustainable forest ecosystem restoration. Copyright © 2017 John Wiley & Sons, Ltd.     

Intensification of agriculture on vertisols to minimize land degradation in parts of the Ethiopian Highlands

This paper highlights some interventions which might alleviate agricultural pressures on steep slopes and reduce land degradation in parts of the Ethiopian Highlands. The Ethiopian Highlands are losing alarming amounts of soils (estimated at more than one billion, 1000 million, tonnes) annually. This loss, which is associated with nutrient losses, is manifest in declining agricultural production and biodiversity. About 80 per cent of the annual soil loss occurs from croplands during the rainy season. The nutrient imbalance is further accentuated by forest clearing, removal of crop residue from cultivated lands, and little use of chemical fertilizers or organic manure. Even where livestock are part of the production system, dung is preferentially used as a cooking fuel. Chemical fertilizers are costly, and therefore and alternative land-management scheme is suggested. This is based on a new land-shaping device for drainage which is called the BBM (broad-bed maker), and growing forage legumes to improve soil nutrients, which should allow intensive cultivation of Vertisols in the Ethiopian Highlands. Adoption of the broad bed and furrow land-management system would facilitate early planting and increase the yield of both grain and straw from the major crops relative to the yield from traditional cultivation in flat beds. While not decreasing the yield of grain, mixed cropping of grain and forage crops has been shown to give significantly greater total crop residue yields. The yield is even greater when fertilizers are applied. Supplementary irrigation can help in utilizing Vertisols on bottom lands, and this can be expedited by constructing water reservoirs.     

Soil loss and run‐off characteristics under different soil amendments and cropping systems in the semi‐deciduous forest zone of Ghana

Soil erosion is a major constraint to crop production on smallholder arable lands in Sub‐Saharan Africa (SSA). Although different agronomic and mechanical measures have been proposed to minimize soil loss in the region and elsewhere, soil management practices involving biochar‐inorganic inputs interactions under common cropping systems within the framework of climate‐smart agriculture, have been little studied. This study aimed to assess the effect of different soil and crop management practices on soil loss characteristics under selected cropping systems, typical of the sub‐region. A two‐factor field experiment was conducted on run‐off plots under different soil amendments over three consecutive cropping seasons in the semi‐deciduous forest zone of Ghana. The treatments, consisting of three soil amendments (inorganic fertilizer, biochar, inorganic fertilizer + biochar and control) and four cropping systems (maize, soyabean, cowpea, maize intercropped with soyabean) constituted the sub‐plot and main plot factors, respectively. A bare plot was included as a soil erosion check. Seasonal soil loss was greater on the bare plots, which ranged from 9.75–14.5 Mg ha^?1. For individual crops grown alone, soil loss was 31%–40% less under cowpea than under maize. The soil management options, in addition to their direct role in plant nutrition, contributed to significant (p < 0.05) reductions in soil loss. The least soil loss (1.23–2.66 Mg ha^?1) was observed under NPK fertilizer + biochar treatment (NPK + BC) over the three consecutive cropping seasons. Biochar in combination with NPK fertilizer improved soil moisture content under cowpea crops and produced considerably smaller bulk density values than most other treatments. The NPK + BC consistently outperformed the separate mineral fertilizer and biochar treatments in biomass yield under all cropping systems. Biochar associated with inorganic fertilizers gave economic returns with value–cost ratio (VCR) > 2 under soyabean cropping system but had VCR < 2 under all other cropping systems. The study showed that biochar/NPK interactions could be exploited in minimizing soil loss from arable lands in SSA.     

Assessing the extent and causes of forest degradation in India: Where do we stand?

In India, conservation of biodiversity goes hand in hand with human welfare, as millions of people live adjacent or within protected areas and depend upon forests products. The high density and biomass requirements of these households could result in the degradation of forests and loss of biodiversity. We assessed the collection of forest products among households in five sites in the Western and Eastern Ghats of peninsular India: the Kogar region of the Central Western Ghats, the Bandipur and Sigur regions of the Nilgiri Biosphere Reserve, the Kalakad-Mundanthurai Tiger Reserve of the southern Western Ghats and Similipal Tiger Reserve of the northern Eastern Ghats, and tested whether extraction pressure on forests was associated with the proportion of agricultural households, wage labour and population density. We also examined whether data on loss of cover as stated by the State of the Forest Reports was supported by field data. The regions differed in land use: Kogar, KMTR and Similipal were primarily agricultural regions, whereas households engaged in wage labour or in running small businesses were predominant in Sigur and Bandipur. Fuel-wood was collected ubiquitously for household use in all sites, used mainly for domestic requirements and secondarily for generating income. Green leaves for making fertilizer and fodder were collected for household use and did not enter the market. Cattle manure for the global organic coffee industry was a major forest product in Bandipur and Sigur. Extraction pressure on forests was positively associated with the availability of wage labour and was negatively with the proportion of agricultural households. Data from official sources seem inadequate to measure forest degradation in protected forests. Accurate estimation of forest condition through field assessments and remote sensing, and understanding the socio-economic variables associated with forest loss and degradation are needed for the sustainable management of Indian protected areas.     

Effects of soil degradation and management practices on the surface water dynamics in the Talgua River Watershed in Honduras

When tropical forests are felled, subsequent land uses affect surface runoff, soil erosion, and soil compaction. In some cases, they can markedly change the hydrology of a region with disastrous effects on human life. The objective of this paper is to investigate the effect of rainfall on stream hydrology due to conversion of primary forests to agriculture. Near surface water dynamics were compared for three land uses on the steep hillsides in the Talgua River Watershed in Honduras: degraded grass‐covered field; traditional coffee plantation; and primary forest. Infiltration and surface runoff rates were measured using several methods. A clear difference was observed in hydraulic conductivity between the degraded and non‐degraded lands. The degraded grass‐covered hillslopes developed a surface restrictive layer with a low saturated hydraulic conductivity of 8 to 11 mm/hr, resulting in more frequent overland flow than traditional coffee plantation and primary forest. Soils under the latter two land‐use types maintained high infiltration capacities and readily conducted water vertically at rates of 109 and 840 mm/hr, respectively. Dye tests confirmed that the coffee plantation and primary forest both maintained well‐connected macropores through which water flowed readily. In contrast, macropores in the degraded soil profile were filled by fine soil particles. Soils in the degraded grass‐covered field also showed more compaction than soils in the coffee plantation. Copyright © 2004 John Wiley & Sons, Ltd.     

Nitrogen‐enriched compost application combined with plant growth‐promoting rhizobacteria (PGPR) improves seed quality and nutrient use efficiency of sunflower

Ecological benefits associated with plant growth‐promoting rhizobacteria (PGPR) inoculants offer a promising integrated nutrient management option to counteract plant nitrogen (N) deficiency. We performed field experiments to evaluate the effect of integrated N fertilizer regime involving chemical N fertilizer (CNF) and N‐enriched compost (NEC), either alone or combined with selected PGPR (Pseudomonas aeruginosa ) on sunflower seed quality, N use efficiency (NUE) and soil fertility during 2014–2015. We found that integrated N biofertilizer application resulted in significantly higher seed oil concentration, fatty acid composition, and harvest index in both cropping years. Greater effects on N yield efficiency (NYE), N use efficiency (NUE), N physiological efficiency (NPE), and photosynthetic N use efficiency (PNUE) were recorded in nitrogen‐enriched compost+PGPR inoculant (NECPI) treatment followed by chemical N fertilizer+PGPR inoculant (CNFPI) treatment. Statistically significant differences were observed in linoleic and linolenic acid, NYE, and NUE for treatment × year interaction, thus, suggesting that the integrated N biofertilizer approach facilitates the efficient N use by sunflower for improving yield and seed quality. Moreover, we also found considerable enhancement of soil N fertility after two consecutive cropping years of sunflower. The enhancement of seed quality, N use efficiencies, and soil N fertility through integrated N biofertilizer application emphasizes the importance of balanced crop N nutrition, ensuring sufficient N supply to sunflower with adequate N balance in soil for the next crop. Overall, combination of PGPR with NEC amendment may optimize N uptake efficiency and reduce N fertilizer losses, which is necessarily required for the sustainable sunflower production.     

Improving agroforestry in sandy subhumid northwestern Shandong,China

A highly productive sustainable agroforestry system was established on degraded sandy soils in Gaotang County in the northwestern region of Shandong Province. Five pre‐existing types of land use were compared. Of these, cropping without forest protection would not be sustainable because of wind erosion, while the benefits from extensive forest stretches are extremely low. Sandy soils in this region could be effectively used by agroforestry systems. The profitability and sustainability of the system depends on proportions and arrangements of trees and crops. The locally developed agroforestry was dramatically improved. In the improved system, tree areas were considerably reduced and intercropping of fruit‐tree‐crop and crop‐crop were increased. The locally developed agroforestry is already ten times more profitable than extensive forest stretches offering minimum shading and root competition, or eight times more than extensive forest stretches offering maximum shading and root competition. Profit from the improved agroforestry is about threefold that of the locally developed agroforestry system. Other sandy regions in China and elsewhere in Asia and Africa could profit from a similar integrated approach, as described here. Copyright © 2003 John Wiley & Sons, Ltd.     

A simple,low‐cost technique for in situ measurement of leaf P concentration in field‐grown rice

Simple tools for diagnosing crop nutritional status are in great demand by agricultural extension staff, particularly in low‐fertility environments. We developed the first practical method for in situ diagnosis of phosphorus (P) nutrition in field‐grown cereal crops by using a handheld colorimeter. The concentration of P in extracts from fresh leaves of lowland rice grown under various P availabilities was closely correlated with that of oven‐dried leaves measured with the standard molybdenum‐blue method in the laboratory, over a range of values from 0.319 to 1.420 mg P g ^?1 DW (r = 0.885^**, n = 14). It takes only 3–5 min to estimate the P concentration of plant samples using the new technique. Although not as accurate as the laboratory method, the new method can easily detect P deficiency of rice in the field (and possibly other cereal crops) without requiring costly, off‐site equipment. Thus, extension staff and agronomists can easily adopt this technique.     

Land Degradation Controlled and Mitigated by Rubber‐based Agroforestry Systems through Optimizing Soil Physical Conditions and Water Supply Mechanisms: A Case Study in Xishuangbanna,China

Different rubber‐based agroforestry systems are adopted to control and mitigate land degradation. However, the soil physical conditions and soil hydrological processes of different agroforestry systems are still unclear. Thus, in this study, rubber (Hevea brasiliensis ) monoculture, rubber and Clerodendranthus spicatus agroforestry system (RCS) and rubber and Amomum villosum agroforestry system (RAV) were developed from a degraded land that had similar backgrounds of terrain and management measures for 50 years. Conventional methods were applied, and dye tracer experiments were conducted to measure the soil physical conditions and determine the water movement in soil. After 5 years' growth, both RCS and RAV could effectively promote the soil physical conditions and optimize soil structure by improving the proportion of the three soil phases. Favourable soil properties, multiple‐layered canopies and ground cover in agroforestry systems could promote the formation of three‐dimensional hydraulic redistribution in soil profile. The infiltration of rainfall into the soil was enhanced; meanwhile, surface runoff and soil erosion were mitigated, and then more water was transported, redistributed and stored into the different soil layers by the more dominant preferential flow, water exchange and lateral flow in soil profiles. These water supply mechanisms could allow planting intercrops with rubber trees to uptake water from different water sources and coexist in an agroforestry system. Our results highlighted that rubber‐based agroforestry systems are a useful management practice to maximize the utilization of land and water resources. Copyright © 2017 John Wiley & Sons, Ltd.     

Soil fertility and bacterial community composition in a semiarid Mediterranean agricultural soil under long-term tillage management

This research attempted to investigate a part of the United Nations sustainable development goal 15, dealing with preventing land degradation and halting the loss of microorganisms’ diversity. Since soil deterioration and biodiversity loss in the Mediterranean area are occurring because of intensive management, we evaluated some biochemical and microbiological parameters and bacterial biodiversity under long-term conventional tillage (CT) and no-tillage (NT) practices, in Basilicata, a typical Region of Southern Italy, characterized by a semiarid ecosystem. The highest biological fertility index (BFI) (composed of soil organic matter, microbial biomass C, cumulative microbial respiration during 25 days of incubation, basal respiration, metabolic quotient and mineralization quotient) was determined for the 0–20 cm of NT soil (class V, high biological fertility level). The analysis of the taxonomic composition at the phylum level revealed the higher relative abundance of copiotrophic bacteria such as Proteobacteria, Actinobacteria and Bacteroidetes in the NT soil samples as compared to the CT soil. These copiotrophic phyla, more important decomposers of soil organic matter (SOM) than oligotrophic phyla, are responsible of a higher microbial C use efficiency (CUE) in tilled soil, being microbial community composition, C substrates content and CUE closely linked. The higher Chao1 and Shannon indices, under the NT management, also supported the hypothesis that the bacterial diversity and richness increased in the no-till soils. In conclusion, we can assume that the long-term no-tillage can preserve an agricultural soil in a semiarid ecosystem, enhancing soil biological fertility level and bacterial diversity.     

Degradation and abandonment of mechanized rain‐fed agricultural land in the Southern Gadarif region,Sudan: the local farmers' perception

In the Gadarif Region of Sudan, destruction of the natural vegetation for agricultural expansion is one of the major causes of the degradation of renewable resources and the environment. This study identifies and analyses the farmers' attitudes and perceptions towards agricultural land degradation and abandonment. The cross‐sectional data collected from ten key informants and 41 large‐scale farmers focussed on the degradation and abandonment of mechanized agricultural land. The results of the study show that the respondents are well aware that soil degradation is in various forms are taking place on their cultivated agricultural land. This is based on their perception and interpretation of indicators such as weed infestation, poor soil fertility and soil compaction. Continuous cropping, mono‐cropping, rainfall shortage and the use of inferior seeds are the main reasons of land degradation as indicated by farmers. The main measures acknowledged to maintain and improve land productivity are repeated soil ploughing, abandonment/fallow periods and crop rotation. The study adduces evidence of widespread land degradation. The mitigation measures followed by the farmers may though not be sufficient to restore the soil fertility. The application of appropriate chemical fertilizers, sound crop rotation and long fallow periods can be recommended. Any management and research intervention regarding the problem of land degradation should; however, be concerted with the farmers' knowledge. Copyright © 2009 John Wiley & Sons, Ltd.     

Nutrient concentrations and acidity in ferralitic soil under perennial cropping, fallow and primary forest in central Amazonia

The long‐term productivity on the acidic, nutrient‐poor upland soils of central Amazonia depends to a large extent on the chemical soil fertility as influenced by vegetation type and management. We compared soil and soil solution data from permanent cropping, fallow and primary forest on a Xanthic Ferralsol in central Amazonia to evaluate changes of soil fertility following forest conversion, agricultural use at different intensities and setting aside agricultural land. The agricultural systems included a perennial polyculture at two fertilizer inputs and a monoculture plantation. Soil and soil solution were collected to 2 m depth, and the soil solution was monitored over 2 years. Both soil and soil solution data showed decreasing soil fertility in the sequence: monoculture and polyculture at large input, polyculture at small input, forest and fallow. The soil solution data were more sensitive to effects of systems and fertilizer inputs on subsoil fertility. Fractionation of the N in the soil solution showed a larger proportion of dissolved organic N in the N‐poor fallow soil than in the soil under forest and agriculture. The soil under fallow, forest and low‐input agriculture had larger exchangeable acidity than that under high‐input agriculture, but the Al concentrations in the soil solution were very small because there were few cations with which to exchange and less nitrification. In high‐input agriculture, pronounced acidification peaks in the topsoil solution followed fertilization. The comparison of soil and soil solution data explained why the spontaneous vegetation thrives at very large exchangeable acidity in these soils, whereas agricultural systems often depend on liming to reduce the concentration of toxic Al in the soil.     

雷州半岛桉树人工林土壤肥力特征及其成因

对雷州林业局桉树人工林地进行了土壤普查,结果表明,桉树人工林土壤肥力很低;其现状肥力特征的形成与桉树人工林生态系统水土流失严重,人为因素对土壤养分生物积累过程的干扰,桉树全树利用方式,耕垦和采后剩余物处理不适当有关。因此,增加桉树人工林生物多样性、回归林地凋落物于土壤,应用适当地采伐利用方式和采伐剩余物的处理方式,是改善桉树人工林土壤肥力必须采取的措施。     

Agricultural sustainability in Turkey: integrating food,environmental and energy securities

Agricultural production in Turkey is not sustainable due to degradation and loss of croplands, rapid population growth, and inequitable economic growth (poverty and overconsumption). Degrading land uses and management practices disturb the life‐supporting biogeochemical cycles within croplands and between croplands and natural ecosystems by increasing emissions of greenhouse gases (GHGs: CO₂, CH₄, N₂O, CFCs, and tropospheric O₃), pollution of water, soil and air, loss of soil organic matter and biodiversity, erosion, salinization and desertification. Sustainability‐oriented management practices in croplands include maintenance of soil organic matter by conservation tillage and residue management, windbreaks, selection of crops ecologically adapted to local climate regimes, efficient crop rotation, enhancement of agrobiodiversity (e.g. intercropping and agroforestry), and adoption of proper drainage techniques. Implementation of these preventive and mitigative measures necessitates internalization of ecological principles into agricultural policy and management processes. This study explores the opportunities and limitations of agricultural sustainability in Turkey in a holistic manner. A multiple linear regression (MLR) model was developed to relate CO₂ emissions to energy intensity (energy use/gross domestic product), affluence (gross domestic product/population) and population growth. Our MLR model with a high R² of 97 per cent revealed that stabilization of human population growth, and increasing energy efficiency in economic growth are essential to decreasing GHG emissions and enhancing environmental quality. Copyright © 2002 John Wiley & Sons, Ltd.     

Soil mapping for land‐use planning in a karst area of N Thailand with due consideration of local knowledge

For the development of sustainable land‐management systems in the highlands of N Thailand, detailed knowledge about soil distribution and soil properties is a prerequisite. Yet to date, there are hardly any detailed soil maps available on a watershed scale. In this study, soil maps on watershed level were evaluated with regard to their suitability for agricultural land‐use planning. In addition to common scientific methods (as underlying the WRB classification), participatory methods were used to exploit local knowledge about soils and to document it in a “Local Soil Map”. Where the WRB classification identified eight soil units, the farmers distinguished only five on the basis of soil color and “hardness”. The “Local Soil Map” shows little resemblance with the detailed, patchy pattern of the WRB‐based soil map. On the contrary, the “Local Soil Map” is fairly similar to the petrographic map suggesting that soil color is directly related to parent material. The farmers' perception about soil fertility and soil suitability for cropping could be confirmed by analytical data. We conclude that integrating local soil knowledge, petrographic information, and knowledge of local cropping practices allows for a rapid compilation of information for land‐evaluation purposes at watershed level. It is the most efficient way to build a base for regional land‐use planning.     

Effect of In Situ Water Harvesting Techniques on Soil and Nutrient Losses in Semi‐Arid Northern Ethiopia

Land degradation, mainly due to soil erosion and nutrient losses, is a global problem for sustainable agriculture. Farmlands in the Ethiopian highlands are susceptible to water erosion because of steep slopes and extensive cultivation. A field experiment was conducted in the Gule sub‐watershed in northern Ethiopia to assess the efficacy of in situ water harvesting techniques in reducing soil and nutrient losses. The research was carried out on a sandy clay loam soil under semi‐arid conditions. Soil erosion and nutrient losses were monitored during the rainy season (June to September) in 2013 and 2014. Five treatments with tied ridges, wheat‐straw mulch and effective microorganisms, alone or in combination, and an untreated control were tested. Combined tied ridges and straw mulch, with and without effective microorganisms, significantly reduced average soil loss over the two rainy seasons by 82 and 90% respectively compared with the control. Tied ridges alone reduced average soil loss by 60%. Straw mulch with and without effective microorganisms decreased average soil loss by 81 and 85% respectively. Combined tied ridges and straw mulch significantly decreased average total nitrogen and total phosphorus losses by 82 and 83% respectively. Average nutrient losses were also significantly decreased by tied ridges (59% for nitrogen, 52% for phosphorus) and straw mulch (63% for nitrogen, 68% for phosphorus). Our results indicated that in situ water harvesting techniques can effectively reduce soil and nutrient losses from farmland and were more efficient when the techniques were combined. Copyright © 2016 John Wiley & Sons, Ltd.     

Coffee‐husk biochar application increased AMF root colonization,P accumulation,N2 fixation,and yield of soybean grown in a tropical Nitisol,southwest Ethiopia

Low soil fertility and soil acidity are among the major bottlenecks that limit agricultural productivity in the humid tropics. Soil management systems that enhance soil fertility and biological cycling of nutrients are crucial to sustain soil productivity. This study was, therefore, conducted to determine the effects of coffee‐husk biochar (0, 2.7, 5.4, and 16.2 g biochar kg^?1 soil), rhizobium inoculation (with and without), and P fertilizer application (0 and 9 mg P kg^?1 soil) on arbuscular mycorrhyzal fungi (AMF) root colonization, yield, P accumulation, and N₂ fixation of soybean [Glycine max (L.) Merrill cv. Clark 63‐K] grown in a tropical Nitisol in Ethiopia. ANOVA showed that integrated application of biochar and P fertilizer significantly improved soil chemical properties, P accumulation, and seed yield. Compared to the seed yield of the control (without inoculation, P, and biochar), inoculation, together with 9 and 16.2 g biochar kg^?1 soil gave more than two‐fold increment of seed yield and the highest total P accumulation (4.5 g plant^?1). However, the highest AMF root colonization (80%) was obtained at 16.2 g biochar kg^?1 soil without P and declined with application of 9 mg P kg^?1 soil. The highest total N content (4.2 g plant^?1) and N₂ fixed (4.6 g plant^?1) were obtained with inoculation, 9 mg P kg^?1, and 16.2 g biochar kg^?1 soil. However, the highest %N derived from the atmosphere (%Ndfa) (> 98%) did not significantly change between 5.4 and 16.2 g kg^?1 soil biochar treatments at each level of inoculation and P addition. The improved soil chemical properties, seed yield, P accumulation and N₂ fixation through combined use of biochar and P fertilizer suggest the importance of integrated use of biochar with P fertilizer to ensure that soybean crops are adequately supplied with P for nodulation and N₂‐fixation in tropical acid soils for sustainable soybean production in the long term.     

Nutrient mobilization and nutrient contents of Zea mays in response to EDTA additions to heavy‐metal‐contaminated agricultural soil

Enhanced phytoextraction of heavy metals (HMs) using chelating agents and agricultural crops is widely tested as remediation technique for agricultural soils contaminated with less mobile HMs. Nutrients are complexed by chelating agents simultaneously to HMs. In this study, the effect of EDTA (ethylenediaminetetraacetic acid) application on nutrient mobility in the soil and nutrient contents of Zea mays was tested on the laboratory and on the field scale. EDTA effectively increased the mobility of total water‐soluble macronutrients (Ca, K, Mg, P) and micronutrients (Fe, Mn) in the soil solution. Thereby nutrient co‐mobilization did cause competition to target HMs during the phytoextraction process. Mobilization was caused by complexation of nutrient cations by negatively charged EDTA and by dissolution of oxides and hydroxides. Increased concentrations of negatively charged P indicate the dissolution of metal phosphates by EDTA. Higher total water‐soluble nutrient concentrations enhanced bioavailability and plant contents of all determined nutrients especially that of Fe. Mobilization of nutrients may result in leaching and loss of soil fertility.     

A systems analysis of soil and forest degradation in a mid‐hill watershed of Nepal using a bio‐economic model

Forest degradation, manifested through decline in forest cover, and the resulting soil erosion and organic carbon losses, is a serious problem caused by a complex coupling of bio‐physical, socio‐economic and technological factors in the Himalayan watersheds. Greater understanding of the linkages between these factors requires a systems approach. We have proposed such an approach using a bio‐economic model to explore the system behaviour of forest degradation, soil erosion, and soil C losses in the forest areas. The outcome of the model simulation over a 20‐year period indicates that soil erosion and C loss rates may increase more than four‐fold by the year 2020 under the existing socio‐economic and biophysical regime (the base scenario). Reductions in the population growth rate, introduction of improved agricultural technology and increase in the prices of major agricultural crops can help slow down the rates of forest decline, soil erosion and C loss or even stabilize or reverse them. The results suggest that economic incentives may be highly effective in the reduction of soil loss, as well as C release to the atmosphere. Copyright © 2005 John Wiley & Sons, Ltd.