Risk Of Leaching Research Articles

Effects of Typical Chemical Agents on Preventing Pollution and Controlling Drought in a Cherry Orchard

In the North China plain, serious Non-point-source (NPS) pollution and drought are two great concerns in agricultural production. In our studies, two typical chemical agents ( SAP and FA ) were selected to control drought and pollution in a cheery orchard. Soil water content, nutrient transport in soil profile have been researched. The results showed that the soil water content of treatments with chemical agents increased maximally by 19.4% relative to treatment without chemical agents, and increased by 35.2% for Ammonium-N in 20-60 cm soil layer ( main root zone ). However, in 60-120 cm deeper soil layer, the water leakage of treatments with chemical agents decreased averagely by 15.1% relative to treatment without chemical agents, and increased by 43.8% for Nitrate-N. The chemical agents hold water and nutrient in root zone and thus reducing the risk of pollutant leaching into the underground water. It can be found that treatment ( 150kg/h㎡ SAP + 300 times FA ) is the optimal combination group in all treatments. The chemical prevention technology provided a new guide for controlling drought and reducing NPS pollution in cherry planting in the North China plain.

Crop Production and Environmental Effects in Conventional and Organic Vegetable Farming Systems: The Case of a Long-Term Experiment in Mediterranean Conditions (Central Italy)

Monsampolo Organic VEgetable (MOVE) long-term field experiment produced a comparison between organic and a conventionally managed agroecosystem for vegetable production in Central Italy. The study was based on a four-year crop rotation involving six main crops: tomato, melon, fennel, lettuce, cauliflower, and bean. The experiment started in 2001. The agronomic performance and environmental sustainability of the two different management systems were assessed over a three-year period (2007–2010), comparing a) the yield and produce quality; b) cultivar adaptability to organic farming conditions; c) soil quality; and d) potential risk of soil nitrogen leaching. The organic and conventional four-years rotation systems yielded similarly and most of the crops showed no significant differences in produce quality. The study also indicates that comparisons among cultivars to be used in organic farming should be carried out on such experimental field sites where organic farming management had been in place for the long term. Our study demonstrated that soil organic C and total N increased, respectively, of 37% and 22% in the organically managed vegetable production system as compared to the conventional one. The risks of soil nitrate leaching were higher in autumn/winter conventionally managed crops as compared to the organic ones.

Effects of sewage sludge biochar on plant metal availability after application to a Mediterranean soil

Pyrolytic conversion of sewage sludge into biochar could be a sustainable management option for Mediterranean agricultural soils. The aim of this work is to evaluate the effects of biochar from sewage sludge pyrolysis on soil properties; heavy metals solubility and bioavailability in a Mediterranean agricultural soil and compared with those of raw sewage sludge. Biochar (B) was prepared by pyrolysis of selected sewage sludge (SL) at 500°C. The pyrolysis process decreased the plant-available of Cu, Ni, Zn and Pb, the mobile forms of Cu, Ni, Zn, Cd and Pb and also the risk of leaching of Cu, Ni, Zn and Cd. A selected Mediterranean soil was amended with SL and B at two different rates in mass: 4% and 8%. The incubation experiment (200d) was conducted in order to study carbon mineralization and trace metal solubility and bioavailability of these treatments. Both types of amendments increased soil respiration with respect to the control soil. The increase was lower in the case of B than when SL was directly added. Metals mobility was studied in soil after the incubation and it can be established that the risk of leaching of Cu, Ni and Zn were lower in the soil treated with biochar that in sewage sludge treatment. Biochar amended samples also reduced plant availability of Ni, Zn, Cd and Pb when compared to sewage sludge amended samples.

Clay soil moisture in spring cereal cultivation as related to tillage management

Conservation tillage with crop covered soil surface has been found to reduce the risk of erosion and nutrient leaching. The reduction of tillage intensity changes topsoil structure affecting soil physical conditions relevant to crop growth. In this study, the effects of autumn tillage management on soil moisture during the growing season of spring barley (Hordeum vulgare) was examined on two fi eld experiments on clay soils (Vertic Cambisol, Eutric Cambisol) in southwestern Finland in 2004–11. The objective of the study was to investigate the effects of reduced tillage intensity on soil moisture conditions of two different clay soils in different weather conditions. Autumn mouldboard ploughing (to 20–25 cm depth, P) was compared to stubble cultivation (10–15 cm, S) and zero tillage (N). During the growing season, soil moisture was determined once a week at the depth of 0−30 cm with a TRASE system I (Time Domain Refl ectometry (TDR)). Daily weather conditions (precipitation, air temperature) were also determined. Zero tilled soil stayed moister than the soil in other tillage treatments. When the beginning of the growing season was dry, higher soil moisture content in zero tilled soil improved the growth conditions of barley. In an unexceptional rainy beginning of growing season, the wetness of clay soils in zero tilled treatment hampered the crop growth and yield production clearly.

Research on the Influence of Irrigation Amount on Dynamic Changes and Accumulation of Soil Nitric Nitrogen under Film Hole Irrigation

Through the experiment of different Irrigation Amounts with urea applied, the paper studied the influence of Irrigation Amounts on soil nitric nitrogen dynamical changes under film hole irrigation and the nitric nitrogen content of the growing period was determined. The result showed: different irrigation amount in the profiles being 3cm and 8cm away from the film hole center, it appeared nitric nitrogen accumulation peaks, increased the irrigation amount promoted the transformation of urea, increased the transformed nitric nitrogen content and distribution of nitric nitrate and the risk of nitric nitrate leaching. In the profiles being 3cm away from the film hole center, the nitric nitrogen accumulation peak significantly reduced at harvest stage, but it reduced in the profiles being 8cm away from the film hole center at milky stage. The milky stage was the maximum period when the corn uptook nitrogen at different irrigation amount. Increased irrigation amount lower the accumulation content of nitric nitrogen near the film hole center after harvest, and higher the accumulation content of nitric nitrogen far away from the film hole center. Above researches could provide the basis for rational fertilization of farmland and nitrate environmental impacts on assessment.

A review of farm level responses to nutrient regulations in Manitoba, Canada

Abstract Since 1998, the Province of Manitoba in Canada has regulated livestock manure management by linking manure application to crop removal rates. Initial concerns over the risk of excessive nitrate leaching led to regulation based on nitrate-nitrogen build up in soils. This regulation failed to identify problems related to other nutrients, especially phosphorus and its impact on blue-green algae (cyanobacteria) in Lake Winnipeg. New regulations have been enacted to limit phosphorus accumulations in soil. Livestock producers, including hog farmers, were particularly concerned with these new regulations as most crops need less phosphorus than was being supplied in livestock manure when application was based on nitrogen needs. The actual response to the regulation has been much different than the forecasts. The implementation of a new enzyme, phytase, has reduced the level of phosphorus in hog manure (and lowered feed costs!). The increase in nitrogen and phosphorus fertilizer prices has also increased ...

Field-scale analysis of water and nutrient use efficiency for vegetable production in a West African urban agricultural system

Urban agriculture increasingly supplies food and non-food services to the rapidly growing West African cities. However, with its typically heavy use of fertilizers and uncontrolled use of water, it bears severe risks of soil and groundwater pollution. This study was carried out in Bobo Dioulasso (Burkina Faso, West Africa) at two commercial gardening sites. It aimed at performing a detailed characterization of farmer’s water and nutrient management strategies. Four vegetable crops were monitored (tomato, cabbage, carrot and lettuce). Water inputs (rainfall and irrigation), nutrient inputs (organic and mineral fertilizers and nutrients in irrigation water) and crop uptake were monitored over a 1–2-year period. In addition, pan lysimeters allowed monitoring drainage. Depending on the site, 3–8% of the input water was lost by drainage, i.e., as much as 293 mm/year at one of the sites. During the dry season, when the farmer has full control over the water supply, water application exceeded plant requirements by as much as 40%, which reveals inefficient water use. Up to 800 kg N ha−1, 140 kg P ha−1 and 500 kg K ha−1 were applied for a single crop cycle. With few exceptions, crops tended to be strongly over-fertilized, except for K at one of the two sites. Nutrient supply exceeded crop requirements by 109 to 2,012 kg N, 66 to 450 kg P and 0 to 393 kg K per year. These results, in combination with the large observed rates of drainage, are indicative of a high risk of nutrient leaching and groundwater contamination. The partial factor productivity of nutrients tended to be low. These results therefore suggested that there is scope to substantially reduce nutrient application rates in these systems without adverse effects on yields, which would be beneficial for groundwater resources and improve the economic returns.

Establishment of winter wheat—Strategies for reducing the risk of nitrogen leaching in a cool-temperate region

Different strategies for establishment of winter wheat were studied in six field experiments in southern and south-western Sweden examining accumulation of soil mineral nitrogen (SMN) during autumn and winter. Conventional tillage (CT), reduced tillage (RT) and non-tillage (NT) and early (1) and late (2) time of tillage were tested in combination with early (1) and late (2) sowing (S) times, including different time intervals between tillage and sowing. Amount of SMN in November followed the treatment order: CT1 S1<RT1 S1<NT S1<CT2 S2<RT2 S2<NT S2<RT1 S2<CT1 S2 in field trials where glyphosate was applied early in autumn and the order: CT1 S1<RT1 S1<NT S1<RT2 S2<CT2 S2<RT1 S2<CT1 S2 in field trials where no glyphosate was applied. Autumn SMN was reduced by 14–24kgha−1 when sowing was carried out immediately after early tillage compared with 3–4 weeks after tillage. This could not be attributed to a direct effect of tillage on N mineralisation, but to differences in crop and weed uptake of N. With the same time interval between tillage and sowing, in general there were no significant differences between tillage methods. Sowing time did not affect winter wheat yield. The results demonstrated the importance of a well-established winter crop and of the combined timing of tillage, sowing date and application of glyphosate or other herbicides in reducing nitrogen leaching.

The use of a nitrification inhibitor (DCn™) to reduce nitrate leaching under a winter-grazed forage crop in the Central Plateau

Grazing of brassica winter forage crops returns large amounts of excreted nitrogen (N) back to the paddock during winter when risk of leaching is high. This experiment measured nitrate-N leaching below 60 cm of 132 and 173 kg N/ha following June grazing by dairy cows of swede/kale crops in 2008 and 2009. Application of DCD immediately after grazing plus 6 weeks later decreased leaching by 20-27% (significant at P

Clay soil moisture in spring cereal cultivation as related to tillage management

Conservation tillage with crop covered soil surface has been found to reduce the risk of erosion and nutrient leaching. The reduction of tillage intensity changes topsoil structure affecting soil physical conditions relevant to crop growth. In this study, the effects of autumn tillage management on soil moisture during the growing season of spring barley ( Hordeum vulgare ) was examined on two fi eld experiments on clay soils (Vertic Cambisol, Eutric Cambisol) in southwestern Finland in 2004–11. The objective of the study was to investigate the effects of reduced tillage intensity on soil moisture conditions of two different clay soils in different weather conditions. Autumn mouldboard ploughing (to 20–25 cm depth, P) was compared to stubble cultivation (10–15 cm, S) and zero tillage (N). During the growing season, soil moisture was determined once a week at the depth of 0−30 cm with a TRASE system I (Time Domain Refl ectometry (TDR)). Daily weather conditions (precipitation, air temperature) were also determined. Zero tilled soil stayed moister than the soil in other tillage treatments. When the beginning of the growing season was dry, higher soil moisture content in zero tilled soil improved the growth conditions of barley. In an unexceptional rainy beginning of growing season, the wetness of clay soils in zero tilled treatment hampered the crop growth and yield production clearly.

Salinity and sodicity affect soil respiration and dissolved organic matter dynamics differentially in soils varying in texture

The individual effects of salinity and sodicity on organic matter dynamics are well known but less is known about their interactive effects. We conducted a laboratory incubation experiment to assess soil respiration and dissolved organic matter (DOM) dynamics in response to salinity and sodicity in two soils of different texture. Two non-saline non-sodic soils (a sand and a sandy clay loam) were leached 3–4 times with solutions containing different concentrations of NaCl and CaCl2 to reach almost identical electrical conductivity (EC1:5) in both soils (EC1:5 0.5, 1.3, 2.5 and 4.0 dS m−1 in the sand and EC1:5 0.7, 1.4, 2.5 and 4.0 dS m−1 in the sandy clay loam) combined with two sodium absorption ratios: SAR < 3 and 20. Finely ground wheat straw residue was added (20 g kg−1) as substrate to stimulate microbial activity. Cumulative respiration was more strongly affected by EC than by SAR. It decreased by 8% at EC 1.3 and by 60% at EC 4.0 in the sand, whereas EC had no effect on respiration in the sandy clay loam. The apparent differential sensitivity to EC in the two soils can be explained by their different water content and therefore, different osmotic potential at the same EC. At almost similar osmotic potential: −2.92 MPa in sand (at EC 1.3) and −2.76 MPa in the sandy clay loam (at EC 4.0) the relative decrease in respiration was similar (8–9%). Sodicity had little effect on cumulative respiration in the soils, but DOC, DON and specific ultra-violet absorbance (SUVA) were significantly higher at SAR 20 than at SAR < 3 in combination with low EC in both soils (EC 0.5 in the sand and EC 0.7 and 1.4 in the sandy clay loam). Therefore, high SAR in combination with low EC is likely to increase the risk of DOC and DON leaching in the salt-affected soils, which may lead to further soil degradation.

Long-term simulations of nitrate leaching from potato production systems in Prince Edward Island, Canada

LEACHN was employed to simulate nitrate leaching from a representative potato production system in Prince Edward Island (PEI), Canada and enhance the understanding of impacts of potato (Solanum tuberosum L.) production on groundwater quality. The model’s performance on predicting drainage was examined against water table measurements through coupled LEACHN and MODFLOW modeling. LEACHN was calibrated and verified to data from tile-drain leaching experiments of potato grown in rotation with barley (Hordeum vulgare L.) and red clover (Trifolium pratense L.) during 1999–2008. Long-term simulations using the calibrated model were performed to evaluate the effects of climate and N fertilization for the potato crop on nitrate leaching. The modeling suggests LEACHN can be an effective tool for predicting nitrate leaching from similar cropping systems in PEI. Both measurements and simulations showed nitrate leaching primarily occurred during the non-growing season when crop uptake diminishes, and nitrate from mineralization and residual fertilizer coexists with excessive moisture from rainfall and snowmelt infiltration. Annual average nitrate leaching following potato, barley and red clover phases was predicted to be 81, 54 and 35 kg N ha−1, respectively, and the corresponding leached concentrations were 15.7, 10.1 and 7.3 mg N l−1. Increased N input for potato alone increased nitrate leaching not only during potato phase but also during the rotation crop phases. To reduce the risk of nitrate leaching, practices should be developed to minimize nitrate accumulation in soil both during and outside of the growing season and in both the potato and the rotation crop phases.

Nitrate leaching under maize cropping systems in Po Valley (Italy)

Intensive crop production in Po Valley (Northern Italy) is associated to high risk of nitrate leaching. A multi-year monitoring of soil solution nitrogen was conducted at 6 sites under the ordinary farm management of maize crop ( Zea mays L.) in order to assess NO 3–N leaching. The amount of N fertilizer (organic + mineral) varied from 209 to 801 kg N ha −1 year −1. Maize biomass ranged from 15 to 32 t ha −1 and N removal from 150 to 400 kg ha −1. Soil water solution was sampled at five depths along the soil profile (from 0.3 to 1.5 m) at time intervals of 7–30 days using suction cups. Soil water content (SWC) was measured daily by TDR at the same depths of suction cups. Soil water NO 3–N concentrations varied from 0 to 110 mg L −1, with the highest concentrations measured after fertilizer application. Once validated on measured SWC data, SWAP model was applied to estimate the drainage flux. Annual leaching was calculated by multiplying drainage flux by soil water NO 3–N concentration. N Leaching ranged from 14 to 321 kg ha −1 year −1, according to fertilization, crop N removal, rainfall, irrigation management, and it was mainly affected by N surplus.

Simulation of nitrate leaching under potato crops in a Mediterranean area. Influence of frost prevention irrigation on nitrogen transport

Abstract The Sa Pobla area (Majorca Island, Spain) heavily depends on the use of groundwater resources for irrigation and urban water supply and is characterised by the presence of intensive potato farming activities. The Plioquaternary aquifer is unconfined and contains high levels of nitrate concentrations. To analyse the risk of contamination to the aquifer arising from agricultural practices, the amount of water and nitrogen leached below the root zone was simulated by the GLEAMS code. Data for model calibration and validation were obtained from field experiments on six potato crops for the years 2004–2007. When air temperatures drop below 1 °C irrigation water is applied to prevent crops from frost damage. During times of anomalously low air temperatures, the risk of nitrate leaching is increased by as much as 318% from frost prevention irrigation under normal local conditions. The GLEAMS simulation model was successfully calibrated for Sa Pobla conditions under potato cropping as shown by RMSE values for the water transport module of 0.19, 0.14 and 0.13 for the calibration period and 0.20, 0.25 and 0.15 for the validation period at depths of 0.3, 0.6, and 0.9 m respectively; and for the chemical transport module the R2 value was 0.82 for the calibration period and 0.60 for the validation period. Consequently, for Sa Pobla conditions, GLEAMS can be used to assess the effectiveness of different agricultural management practices to reduce nitrate leaching. It was concluded that additional irrigation water applied for frost prevention plays a very important role in nitrate leaching below the root zone, which enhances the nitrogen loading to the aquifer.

Effect of winter cover crop species and planting methods on maize yield and N availability under irrigated Mediterranean conditions

Under semiarid Mediterranean conditions irrigated maize has been associated to diffuse nitrate pollution of surface and groundwater. Cover crops grown during winter combined with reduced N fertilization to maize could reduce N leaching risks while maintaining maize productivity. A field experiment was conducted testing two different cover crop planting methods (direct seeding versus seeding after conventional tillage operations) and four different cover crops species (barley, oilseed rape, winter rape, and common vetch), and a control (bare soil). The experiment started in November 2006 after a maize crop fertilized with 300 kg N ha −1 and included two complete cover crop-maize rotations. Maize was fertilized with 300 kg N ha −1 at the control treatment, and this amount was reduced to 250 kg N ha −1 in maize after a cover crop. Direct seeding of the cover crops allowed earlier planting dates than seeding after conventional tillage, producing greater cover crop biomass and N uptake of all species in the first year. In the following year, direct seeding did not increase cover crop biomass due to a poorer plant establishment. Barley produced more biomass than the other species but its N concentration was much lower than in the other cover crops, resulting in higher C:N ratio (>26). Cover crops reduced the N leaching risks as soil N content in spring and at maize harvest was reduced compared to the control treatment. Maize yield was reduced by 4 Mg ha −1 after barley in 2007 and by 1 Mg ha −1 after barley and oilseed rape in 2008. The maize yield reduction was due to an N deficiency caused by insufficient N mineralization from the cover crops due to a high C:N ratio (barley) or low biomass N content (oilseed rape) and/or lack of synchronization with maize N uptake. Indirect chlorophyll measurements in maize leaves were useful to detect N deficiency in maize after cover crops. The use of vetch, winter rape and oilseed rape cover crops combined with a reduced N fertilization to maize was efficient for reducing N leaching risks while maintaining maize productivity. However, the reduction of maize yield after barley makes difficult its use as cover crop.

Mobilisation of AS and trace metals in saline, acidic Sopolic Technosols: the role of the rhizosphere and flooding conditions

The aim of this work was to study the risk of As and metal pollution in saline wetlands affected by slightly acidic mine wastes, in the presence or absence of a plant rhizosphere, under different flooding regimes. Some guidelines for management will be proposed in order to minimise the risk of metal leaching in metal-polluted salt marshes. A microcosm experiment was conducted to assess the influence of two flooding regimes (continuous or alternating) and the presence of rhizosphere (Sarcocornia fruticosa and Phragmites australis) on the mobilisation of As, Cd, Mn, Pb, Zn and Fe in a slightly acidic, saline Spolic Technosol (pH ≈ 6.5; total concentrations: 551 mg kg−1 As, 5,640 mg kg−1 Pb, 5,299 mg kg−1 Zn). Metal and As pore water concentrations decreased with flooding time (e.g. from approximately 1,700 μg L−1 Cd, 190 mg L−1 Zn and 230 mg L−1 Mn to <400 μg L−1 Cd, <35 mg L−1 Zn, and 50 mg L−1 Mn). A sequential extraction showed that Fe and As were associated mainly with the silicate fraction of the soil, but most of the Mn, Cd, Pb and Zn belonged to the reactive fraction. The rhizosphere of Sarcocornia induced a lower pH, which facilitated higher concentrations of soluble Fe. However, in pots without plants and pots with Phragmites, the combination of Eh and pH led to conditions for formation of siderite, and hence the concentrations of soluble Fe were lower. The concentrations of Mn, Cd, Pb and Zn were lower in vegetated pots, probably due to precipitation of metal carbonates favoured by gas exchange in the rhizosphere. The rhizosphere modified soil conditions during the period of flooding and this affected the dynamics of metals. The high levels of soluble metals pose a risk for leaching, transfer to the food web and toxicity for living organisms. In order to reduce the risks, we propose the water saturation of the soil and the establishments of a plant cover.

An Episodic Transit Time Model for Quantification of Preferential Solute Transport

Variations in the concentrations of naturally occurring isotopes in rainfall provide a “continuous” signal that has the potential to generate more information on how weather conditions control solute transport than traditional field tracer experiments. An isotopically distinct rainfall event can be rapidly transferred through the system when preferential flow occurs. The objective of this study was to develop and test an approach for analyzing how rainfall and soil moisture control preferential transport to tile drains. An episodic solute transit time distributions model that accounts for these effects was developed. The model was tested on artificial data (daily values of tile drain discharge and 18O concentrations in the drainage water) generated by the MACRO model for soils with different potentials for preferential flow. The results showed that the transit time model gave an excellent fit to the artificial data for the soil with a high potential for preferential flow. The dynamics of the preferential flow events were well captured also for the soil with medium potential for preferential flow but the magnitude was sometimes poorly simulated. Once the model parameter values have been determined, the model can be used to calculate the amount and distribution with time of preferential flow to tile drains for all daily rainfall data. Model calculations integrate the soil's potential for preferential flow and the effects of weather conditions and are, therefore, highly relevant as site‐specific indicators for the risk of preferential leaching of agrochemicals. The approach needs to be evaluated against real field data, however, before its usefulness can be established.

Use of Reduced Irrigation Operating Pressure in Irrigation Scheduling. I. Effect of Operating Pressure, Irrigation Rate, and Nitrogen Rate on Drip-irrigated Fresh-market Tomato Nutritional Status and Yields: Implications on Irrigation and Fertilization Management

Increasing the length of irrigation time by reducing the operating pressure (OP) of drip irrigation systems may result in decreased deep percolation and may allow for reduced nitrogen (N) fertilizer application rates, thereby minimizing the environmental impact of tomato (Solanum lycopersicum) production. The objectives of this study were to determine the effects of irrigation OP (6 and 12 psi), N fertilizer rate (100%, 80%, and 60% of the recommended 200 lb/acre N), and irrigation rates [IRRs (100% and 75% of the target 1000–4000 gal/acre per day)] on fresh-market tomato plant nutritional status and yields. Nitrate (NO3−)–N concentration in petiole sap of ‘Florida 47’ tomatoes grown in Spring 2008 and 2009 in a raised-bed plasticulture system was not significantly affected by treatments in both years and were within the sufficiency ranges at first-flower, 2-inch-diameter fruit, and first-harvest growth stages (420–1150, 450–770, and 260–450 mg·L−1, respectively). In 2008, marketable yields were greater at 6 psi than at 12 psi OP [753 vs. 598 25-lb cartons/acre (P &lt; 0.01)] with no significant difference among N rate treatments. But in 2009, marketable yields were greater at 12 psi [1703 vs. 1563 25-lb cartons/acre at 6 psi (P = 0.05)] and 100% N rate [1761 vs. 1586 25-lb cartons/acre at 60% N rate (P = 0.04)]. Irrigation rate did not have any significant effect (P = 0.59) on tomato marketable yields in either year with no interaction between IRR and N rate or OP treatments. Hence, growing tomatoes at 12 psi OP, 100% of recommended N rate, and 75% of recommended IRR provided the highest marketable yields with least inputs in a drip-irrigated plasticulture system. In addition, these results suggest that smaller amounts of irrigation water and fertilizers (75% and 60% of the recommended IRR and N rate, respectively) could be applied when using a reduced irrigation OP of 6 psi for the early part of the tomato crop season. In the later part of the season, as water demand increased, the standard OP of 12 psi could be used. Changing the irrigation OP offers the grower some flexibility to alter the flow rates to suit the water demands of various growth stages of the crop. Furthermore, it allows irrigation to be applied over an extended period of time, which could better meet the crop's needs for water throughout the day. Such an irrigation strategy could improve water and nutrient use efficiencies and reduce the risks of nutrient leaching. The results also suggest that OP (and flow rate) should be included in production recommendations for drip-irrigated tomato.

The dynamics of dissolved organic N in the fumigated soils

The aim of this study was to investigate the dynamics of dissolved organic N in soils fumigated separately with chloropicrin (CP), 1,3-dichloropropene, and metam sodium (MS) for 7 days and then incubated at 25°C for 84 days. The dissolved organic N (DON) at 14 days after fumigation was mainly dissolved amino acids (DAA) which were then rapidly mineralized to ammonium. However, the DON pool at later incubation times was mainly high molecular weight organic N which was resistant to microbial decomposition. Three soil fumigants all increased the proportions of DON in total dissolved N and DAA in DON. Dissolved organic N became much more important mobile N source in CP- and MS-fumigated soils, and this may increase the risks of DON leaching in agricultural ecosystems.

Degradation of Lindane (γ-HCH) in a Mollisol as Effected by Different Soil Amendments

Soil amendments play an important role in management of pesticide residues. In this study, incubation experiment was conducted using the surface (0 - 15 cm) sample of a mollisol supplied with different soil amendments (farmyard manure, cow-dung slurry, pyrite and gypsum) to investigate the effect of amendments on the dissipation of lindane in mollisols. Dissipation of lindane in soil was studied at eight consecutive samplings (0, 1, 3, 5, 7, 10, 15 and 30 d). The results indicated that soil amendments could promote the degradation of lindane in soil. After 30 d of incubation 79% degradation was observed in the untreated soil (without any amendment) whereas, in the case of farmyard manure and cow-dung slurry amended soils, 83% and 91% degradation was observed, respectively. The pyrite and gypsum amendments also enhanced the degradation of lindane in soils, but the effect was less pronounced as compared to the organic amendments. Enhanced degradation in soil treated with organic amendments could be attributed to stimulated microbial activity after the addition of organic amendments. These addition, under different soil management conditions, minimize the persistence of lindane and consequently the risk of leaching and seepage into aquifers.