Potassium Leaching as Affected by Soil Texture and Residual Fertilization in Tropical Soils

Potassium (K) leaching is affected by soil texture and available K, among other factors. In this experiment, effects of soil texture and K availability on K distribution were studied in the presence of roots, with no excess water. Soils from two 6-year field experiments on a sandy clay loam and a clay soil fertilized yearly with 0, 60, 120, and 180 kg ha^?1 of K₂O were accommodated in pots that received 90 kg ha^?1 of K₂O. Soybean was grown up to its full bloom (R2). Under field conditions, K leaching below the arable layer increased with K rates, but the effect was less noticeable in the clay soil. Potassium leaching in a sandy clay loam soil was related to soil K contents from prior fertilizations. With no excess water, in the presence of soybean roots, K distribution in the profile was significant in the lighter textured soil but was not apparent on the heavier textured soil.     

EDTA强化植物修复的环境风险研究

采用柱状盆栽淋溶试验,研究乙二胺四乙酸(EDTA)对有植物生长时,不同浓度Cd处理的土壤中重金属淋溶作用的影响及其动态特征。实验结果表明:土壤重金属Cd处理的浓度为80 mg/kg和160 mg/kg时,加入5 mmol/kg和10 mmol/kg的EDTA,增加了渗滤液中TOC的含量,极大地增加了渗滤液中Cd的含量,且土壤样品中TOC的淋失量和重金属Cd的淋失量都集中发生在淋溶实验的前期。两者相比EDTA对土壤中重金属的活化效应更强,遇到降水,会因淋失对地下水造成严重的重金属污染,应尽量避免在降水期间施用ED-TA。植物根系在渗滤发生的最初期对渗滤有影响,会减少渗滤液的体积,从而减少渗滤液中TOC和重金属的总含量。     

Subsurface Drainage for Rehabilitation of Waterlogged Saline Lands: Example of a Soil in Semiarid Climate

In irrigated agriculture of arid and semiarid regions, soil salinity, coupled with waterlogging, is a serious problem. Provision of subsurface drainage seems to be a prerequisite for optimal crop production. A study was conducted to evaluate the long term (8-year) impact of a subsurface drainage system on soil properties and yields of wheat. The study was located in a severely affected, waterlogged, barren, sandy loamsaline soil (Comborthids). The subsurface drainage system was installed at a 1.75 m depth with three drain spacings (25, 50, and 75 m). The drains facilitated reclamation of the waterlogged saline land which had variations in salt removal with space and time. The removal of salts from the root zone varied initially with distance from the drain and with depth. However, after a few years, the variations were reduced and the land was reclaimed sufficiently to grow most of the crops of the region. Plots provided with a drain spacing of 75 m required more time for complete reclamation compared to plots provided with 25 m drain spacing. Leaching through subsurface drainage increased soil porosity, modulus of rupture, infiltration rate, organic carbon, available nitrogen, phosphorus, potassium, and available water, and decreased bulk density differently in the three drain spacings (20, 50, and 75 m). In the 75 m drain spacing plots, soil salinity (EC e ) and water content remained higher than in the 25 and 50 m drain spacing plots. Soil EC e and water content were less near the drains, were highest in areas midway between the drains, and the effects were more apparent in the summer season. Wheat grain yield decreased with increasing drain spacings in the initial years of reclamation. With the gradual improvement in soil salinity, yields from plots with a 75 m spacing reached those of the narrower drain spacing plots by the fourth year. It was concluded that by installing a subsurface drainage system in a monsoon climate, waterlogged saline soils can be reclaimed by the natural leaching that can take place from rainfall. The optimum yield can be attained with a drain spacing of 75 m, which is 50% more than the design spacing of 50 m. Faster reclamation and more yield were obtained with a 25 m drain spacing and was achieved at a higher cost for the more expensive drainage system.     

Fungal/bacterial ratios in grasslands with contrasting nitrogen management

It is frequently hypothesised that high soil fungal/bacterial ratios are indicative for more sustainable agricultural systems. Increased F/B ratios have been reported in extensively managed grasslands. To determine the shifts in fungal/bacterial biomass ratio as influenced by grassland management and to find relations with nitrogen leaching potential, we sampled a two-year-old field experiment at an organic experimental farm in the eastern part of The Netherlands. The effect of crop (grass and grass-clover), N application rate (0, 40, 80, ) and manure type (no manure, farm yard manure and slurry) on the F/B ratio within three growing seasons was tested, as well as relations with soil and crop characteristics, nitrate leaching and partial N balance. Biomass of fungi and bacteria was calculated after direct counts using epifluorescence microscopy. Fungal and bacterial biomass and the F/B ratio were higher in grass than in grass-clover. The F/B ratio decreased with increasing N application rate and multiple regression analysis revealed a negative relationship with pH. Bacterial activity (measured as incorporation of [³H]thymidine and [¹⁴C]leucine into bacterial DNA and proteins) showed the exact opposite: an increase with N application rate and pH. Leaching increased with N application rate and was higher in grass-clover than in grass. Partial N balance was more positive at a higher N application rate and showed an inverse relationship with fungal biomass and F/B ratio. We conclude that the fungal/bacterial biomass ratio quickly responded to changes in management. Grasslands with higher N input showed lower F/B ratios. Grass-clover had a smaller fungal biomass and higher N leaching than grass. In general, a higher fungal biomass indicated a lower nitrogen leaching and a more negative partial N balance (or smaller N surplus), but more observations are needed to confirm the relationship between F/B ratio and sustainability.     

Soil salinity in Aceh after the December 2004 Indian Ocean tsunami

The 2004 Indian Ocean tsunami inundated about 37,500 ha of coastal farmland in Aceh, and crops planted after the tsunami were severely affected by soil salinity. This paper describes the changes of soil salinity over time on tsunami affected farms and the implications for resuming crop production after natural disasters.Soil salinity and salt leaching processes were assessed across the tsunami affected region by measuring soil apparent electrical conductivity (ECa) using an electromagnetic induction soil conductivity instrument (EM38) combined with limited soil analysis. The ECa was measured 5 times between August 2005 and December 2007 in both the vertical (EMv) and horizontal (EMh) dipole orientations at 23 sites across Aceh. The level of salinity and direction of salt movement were assessed by comparing changes in mean profile ECa and relative changes in EMv and EMh.Eight months after the tsunami the average soil salinity in the 0-1.2 m soil depth varied from ECe 22.6 to 1.6 dS m⁻¹ across sites in the affected region and three years after the tsunami it varied from 13.0 to 1.4 dS m⁻¹. Soil salinity tended to be higher in rice paddy areas that trapped saline tsunami sediments and held seawater for longer periods. Leaching of salts occurred slowly by both vertical displacement and horizontal movement in surface waters. Hence, soil salinity persisted at a level which could reduce crop production for several years after the 2004 tsunami. High soil salinity persisted three years after the tsunami even though there had been more than 3000-7000 mm of accumulated rainfall to leach salts. The slow leaching is likely to have been due to the loss of functional drainage systems and general low relief of the affected areas.Monitoring of soil salinity with EM38 assisted local agricultural extension agencies to identify sites that were too saline for crops and determine when they were suitable for cropping again. The methodology used in this study could be used after similar disasters where coastal agriculture areas become inundated by seawater from storm surges or future tsunamis.     

Conservation tillage and macropore factors that affect water movement and the fate of chemicals

A thorough understanding of how conservation tillage influences water quality is predicated on knowledge of how tillage affects water movement. This paper summarizes the effects of conservation tillage on water movement and quality mainly based on long-term experiments on Luvisols at the North Appalachian Experimental Watershed near Coshocton, OH, USA. Conservation tillage can have a much larger effect on how water moves through the soil than it does on the total amount percolating to groundwater. Soil macroporosity and the proportion of rainfall moving through preferential flow paths often increase with the adoption of conservation tillage and can contribute to a reduction in surface runoff. In some medium- and fine-textured soils most of the water that moves to the subsoil during the growing season (May–October) is probably transmitted by macropores. If a heavy, intense storm occurs shortly after surface application of an agricultural chemical to soils with well-developed macroporosity, the water transmitted to the subsoil by the macropores may contain significant amounts of applied chemical, up to a few per cent, regardless of the affinity of the chemical for the soil. This amount can be reduced by an order of magnitude or more with the passage of time or if light rainstorms precede the first major leaching event. Because of movement into the soil matrix and sorption, solutes normally strongly adsorbed by the soil should only be subject to leaching in macropores in the first few storms after application. Even under extreme conditions, it is unlikely that the amount of additional adsorbed solute transported to groundwater will exceed a few per cent of the application when conservation tillage is used instead of conventional tillage. In the case of non-adsorbed solutes, such as nitrate, movement into the soil matrix will not preclude further leaching. Therefore, when recharge occurs during the dormant season thorough flushing of the soil, whether macropores are present or not, can move the remaining solutes to groundwater. Thus, the net effect of tillage treatment on leaching of non-adsorbed solutes should be minimal.     

稻田氮素淋洗损失研究

采用田间小区试验,连续2年研究了施氮量、分子膜对稻田氮素淋洗损失和氮素平衡的影响,结果表明:稻田以铵态氮淋洗损失最少,90cm处浓度低于0.2mg/L;水稻移栽和烤田后硝态氮浓度达到峰值,以90cm处浓度为0.2～0.9mg/L;整个稻季氮素淋洗量为3.2～5.6kg/hm2,占施氮量的1.4%～2.5%。     

Modelling low molecular weight organic acid dynamics in forest soils

Low molecular weight organic acids such as citrate and oxalate have been hypothesized to play a key role in rhizosphere ecology and pedogenesis. A mathematical site-specific model, DYNLOW, was constructed to describe the temporal and spatial dynamics of these organic acids in coniferous forest soils using the modelling software STELLA^®. Experimentally derived values for biodegradation, adsorption, and daily values of soil temperature, moisture and hydrological flow were used to parameterize the model. The model describes the dynamics and downward movement of oxalate and citrate through the horizons (O, AE, E, Bhs, Bs) of three podzolic soil profiles in Sweden. After calibration, the model predicted average soil solution organic acid concentrations ranging from <1 to 90 μM, which was in agreement with experimental measurements (<1 to 116 μM). The model results indicated that microbial degradation of organic acids was in quantitative terms the biggest process regulating soil solution concentrations. Primary production rates of organic acid in the soil were predicted to be high (<1 to 1250 nmol g⁻¹ soil d⁻¹) in comparison to the amount present at steady state in the soil solution pool (<0.1 to 240 nmol g⁻¹ soil). The downward transfer of organic acids between soil horizons due to mass flow was predicted to be a small flux (<0.1 to 3% of the total loss) compared to that lost by microbial biodegradation. The model predicted that the amount of basal soil respiration that could be attributable to the microbial turnover of organic acids was on average 19±22% of the basal CO₂ production across all sites and horizons for citrate and 7±7% for oxalate. The model results are discussed in the context of pedogenesis, forest soil respiration and organic matter production.     

Comparisons of terrestrial and aquatic bioassays for oil-contaminated soil toxicity

Background  Petroleum products are widely used in various sections of industry and they are one of the most abundant sources of environmental contamination. These products are classified by their physico-chemical properties such as boiling point, density and viscosity. Oil contamination in the environment is primarily evaluated by measuring the chemical concentrations of petroleum products in the solid or water phase. The results of chemical analyses do not correspond directly with the harmful environmental effects of petroleum products on the soil flora and fauna, because the interactions between oil compounds and the production of their methabolites in soil are not measured in chemical assessments. These kinds of effects of complex chemical mixtures in soil can be estimated by bioassays. Therefore, ecotoxicological tests are important for estimating soil quality in the risk assessment of oil-contaminated soil sites. Objectives  The objective of this study was to examine the oil-contaminated soil site of a closed petrol station with both chemical and ecotoxicological methods. The goals of this study were to compare the sensitivity of the terrestrial and aquatic bioassays and to compare the toxicity responses of aquatic bioassays determined from three different extraction procedures. In addition, our aim was to characterise a cost-effective battery of bioassays that could be applied to a comparison of oil-contaminated soils. It was in our interest to investigate oil-contaminated soil with oil concentrations of 2500–12000 mg/kg and to find out the possible differences between terrestrial and aquatic toxicity tests. Methods  Six soil samples from a closed petrol station were examined for toxicity with terrestrial and aquatic tests. Terrestrial tests includedEnchytraeus albidus survival and reproduction assays and seed germination assays using wheat, cress, lettuce, and red clover seeds and growth inhibition assays of onions. The toxicities of the water-extractable fractions of the soil samples obtained from three different extractions were tested with aquatic bioassays based on plants (onion and duckweed growth inhibition tests), microbes (luminescent bacteria test), and enzyme inhibition (reverse electron transport test, RET). Chemical analyses of the solid samples were carried out simultaneously. Results. Oil concentrations ranged from 2500 to 12000 mg/kg, BTEX varied from 300 to 2800 mg/kg, and fuel additives: MTBE and TAME from 0.0 1 to 260 mg/kg. Only the sample contain-ing 12000 mg/kg oil had a significant toxic impact on all test organisms. Soil samples with oil concentrations 2500–6200 mg/ kg had no or only slight adverse effects on the test organisms with one exception, theE. albidus reproduction test. TheE. albidus survival and reproduction tests were the most sensitive bioassays of the terrestrial tests, and the luminescent bacteria test of the aquatic tests.     

Modelling the fate of water and nitrogen in the mixed vegetable farming systems of northern Tasmania, Australia

A combination of high input management systems, high annual rainfall and deep, permeable soils in northern Tasmania create conditions that are conducive to high drainage and nitrogen losses below the root zone. An understanding of the extent and mechanism of such losses will enable farm managers and their consultants to identify and implement more sustainable management practices that minimise potential adverse financial and environmental consequences. Analysing the fate of water and nutrients in farming systems is complex and influenced by a wide range of factors including management, soil characteristics, seasonal climate variability and management history of the paddock/farm in question. This paper describes a novel farm system modelling approach based on the model APSIM, for analysing the fate of nitrogen and water in mixed vegetable-based farming enterprises. The study was based on seven case farms across the Panatana catchment in northern Tasmania. Substantial simulated drainage losses (>100 mm average seasonal loss) were apparent for all crop and rotation elements across all farms in response to the surplus between crop water supply and crop water use. Crop nitrogen demand was found to be close to crop nitrogen supply for all crop and pasture rotation elements with the exception of potato, which had an average surplus nitrogen supply of 89 kg N/ha. This resulted in potato having much higher nitrate nitrogen leaching losses (32 kg N/ha) compared to other crops (<10 kg N/ha). Simulations suggest that practicable management options such as deficit-based irrigation and reduced N fertiliser rates will maintain current levels of productivity while reducing potential offsite N loss and generating significant financial savings via reduced input costs.