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1.
N mineralization in sandy soils of the ‘Fuhrberg well field’ (Hannover) during winter Net N mineralization was measured under field conditions during winter and spring 1991/92 in sandy arable soils (Gleyic Podzols, Mollic Gleysols, Gleyic Arenosols) of the ‘Fuhrberg well field’, a drinking water catchment north-east of Hannover. The aim was to assess leaching losses of nitrate from mineralization processes during the winter on soils formerly used as grassland. Two field procedures were used: the incubation of soil material in polyethylene bags at its original location and rain sheltered fallow plots. Between 6 and 40 (100) kg N ha?1 were mineralized during 73 days from Dec., 17th to March, 2nd. Mineralisation rates were closely correlated to the organic N and C contents of the soils (r2 ± 0.9). In the uncovered soils, the NO3 was completely leached out. On five out of seven fields the process ‘N-mineralization during winter’ alone was sufficient to exceed the official limit for drinking water (50 mg 1?1 NO3? ) in the uppermost groundwater. It is concluded that even 15 years after converting grassland into arable land the Norg and Corg levels in the soils had not reached a new equilibrium.  相似文献   

2.
This paper deals with the problem of mineral N leaching from arable lands due to the fertilization method. The influence of different doses of compost (50 and 100?Mg ha?1) and N-mineral fertilizer (35-70-140 kg N ha?1) on leaching of Nmin in a lysimetric experiment with winter wheat. The area of our interest represents the main source of drinking water for the city of Brno and its neighborhoods. To demonstrate the effect of compost and mineral nitrogen addition, the lysimetric experiment was established there. Seven variants of the experiment with different fertilization schemes were studied during two vegetation seasons (2013 and 2014), each with three repetitions. The experiment was carried out in plastic experimental containers of 0.3 m diameter and 0.5 m height. Therefore, each lysimeter was the same size and was filled with 25 kg of subsoil and 25 kg of topsoil. The highest leaching of Nmin was detected in the variant C2 where 140 kg N ha?1 was applied, in both vegetation periods (5.97 kg Nmin ha?1 after the first vegetation period and 17.02 kg Nmin ha?1 after the second vegetation period). The positive effect of compost application (individually or in combination with the mineral N) on decrease in mineral N leaching was found during both vegetation period in comparison with variant C2. The highest doses of compost (100?Mg per ha) significantly decreased the concentration of mineral nitrogen in the soil eluate in both periods (3.03 kg Nmin ha?1 and 5.79 kg Nmin ha?1, respectively), by 197% and 293% in comparison with variant C2. There is evidence that the application of compost has a positive effect on the reduction of Nmin leaching.  相似文献   

3.
The aim of this study was to evaluate experimentally derived temperature functions for the rate coefficients of net N mineralization in sandy arable soils from NW Germany via field measurements. In part I of this paper (Heumann and Böttcher, 2004), different temperature functions for the rate coefficients of a two‐pool first‐order kinetic equation were derived by long‐term laboratory incubations at 3°C to 35°C. In this paper, field net N mineralization during winter of 25 plots was measured in undisturbed soil columns with a diameter of 20 cm to the depth of the Ap horizon. Mean simulated net N mineralization with the most adequate multiple functions corresponded also best with the mean of the measured values despite of an overestimation of about 10%. Distinctly larger deviations under use of other temperature functions (Arrhenius, Q10) were directly related to their deviations from mean, experimentally derived rate coefficients. Simulated net N mineralization in the soil columns was significantly correlated with measured values, regardless of the temperature functions. Yet the goodness of fit was generally relatively low due to the spatial variability of measured net N mineralization within replicate soil columns, although the mean CV (38%) was by far not extraordinary. The pool of slowly mineralizable N contributed considerably to net N mineralization during four to five winter months, on an average 10.0 kg N ha–1, about one third of total simulated N mineralization. Sometimes, it contributed even 21.3 kg N ha–1, which is almost sufficient to reach the EU drinking‐water limit for nitrate in these soils. Simulations with widely used functions that were once derived from loess soils overestimated mineralization from pool Nslow in the studied sandy arable soils by a factor of two.  相似文献   

4.
Abstract. Large nitrogen (N) inputs to outdoor pig farms in the UK can lead to high nitrate leaching losses and accumulation of surplus N in soil. We investigated the residual effects of three contrasting outdoor pig systems as compared to an arable control on nitrate leaching and soil N supply for subsequent spring cereal crops grown on a sandy loam soil during 1997/98 and 1998/99 harvest seasons. Previously, the pig systems had been stocked for 2 years from October 1995 and were designated current commercial practice (CCP, 25 sows ha?1 on stubble), improved management practice (IMP, 18 sows ha?1 on undersown stubble) and best management practice (BMP, 12 sows ha?1 on established grass). Estimated soil N surpluses by the end of stocking in September 1997 were 576, 398, 265 and 27 kg ha?1 N for the CCP, IMP, BMP and continuous arable control, respectively. Nitrate leaching losses in the first winter were 235, 198, 137 and 38 kg ha?1 N from the former CCP, IMP and BMP systems and the arable control, respectively. These losses from the former pig systems were equivalent to 41–52% of the estimated soil N surpluses. Leaching losses were much smaller in the second winter at 21, 14, 23 and 19 kg ha?1 N, respectively. Cultivation timing had no effect (P>0.05) on leaching losses in year 1, but cultivation in October compared with December increased nitrate leaching by a mean of 14 kg ha?1 N across all treatments in year 2. Leaching losses over the two winters were correlated (P<0.001) with autumn soil mineral N (SMN) contents. In both seasons, spring SMN, grain yields and N offtakes at harvest were similar (P>0.05) for the three previous pig systems and the arable control, and cultivation timing had no effect (P>0.05) on grain yields and crop N offtake. This systems study has shown that nitrate leaching losses during the first winter after outdoor pig farming can be large, with no residual available N benefits to following cereal crops unless that first winter is much drier than average.  相似文献   

5.
Abstract

Nine biennial field experiments, 2000–2004, in south Sweden, 55–56°N, with winter wheat following winter oilseed rape, peas, and oats, were used to estimate the impact of a future milder climate on winter wheat production in central Sweden, 58–60°N. The trials included studies 1) on losses during winter of soil mineral nitrogen (Nmin, 0–90 cm soil), accumulated after the preceding crops in late autumn, 2) on soil N mineralisation (Nnet) during the growing season of the wheat (early spring to ripeness) and 3) on grain yield and optimum N fertilisation (Opt-N rate) of the wheat. Average Nmin in late autumn following winter oilseed rape, peas, and oats was 68, 64, and 45 kg ha?1, respectively, but decreased until early spring. Increased future losses of Nmin during the winter in central Sweden due to no or very short periods with soil frost should enhance the demand for fertiliser N and reduce the better residual N effect of winter oilseed rape and peas, compared with oats. Their better N effect will then mainly depend on larger Nnet (from March to maturity during the winter wheat year). Owing to more plant-available soil N (mainly as Nnet) Opt-N rates were lower after oilseed rape and peas than after oats despite increased wheat yields (700 kg ha?1) at optimum N fertilisation. In addition to these break crop effects, a milder climate should increase winter wheat yields in central Sweden by 2000–3000 kg ha?1 and require about 30–45 kg ha?1 more fertiliser N at optimum N fertilisation than the present yield levels. Increased losses and higher N fertilisation to the subsequent winter wheat in future indicates a need for an estimation of the residual N effect at the individual sites, rather than using mean values as at present, to increase N efficiency.  相似文献   

6.
Nitrogen losses from outdoor pig farming systems   总被引：2，自引：0，他引：2  
Abstract. Nitrogen losses via nitrate leaching, ammonia volatilization and nitrous oxide emissions were measured from contrasting outdoor pig farming systems in a two year field study. Four 1‐ha paddocks representing three outdoor pig management systems and an arable control were established on a sandy loam soil in Berkshire, UK. The pig management systems represented: (i) current commercial practice (CCP) ‐ 25 dry sows ha?1 on arable stubble; (ii) ‘improved’ management practice (IMP) ‐ 18 dry sows ha?1 on stubble undersown with grass, and (iii) ‘best’ management practice (BMP) 12 dry sows ha?1 on established grass. Nitrogen (N) inputs in the feed were measured and N offtakes in the pig meat estimated to calculate a nitrogen balance for each system. In the first winter, mean nitrate‐N concentrations in drainage water from the CCP, IMP, BMP and arable paddocks were 28, 25, 8 and 10 mg NO3 l?1, respectively. On the BMP system, leaching losses were limited by the grass cover, but this was destroyed by the pigs before the start of the second drainage season. In the second winter, mean concentrations increased to 111, 106 and 105 mg NO3‐N l?1 from the CCP, IMP and BMP systems, respectively, compared to only 32 mg NO3‐N l?1 on the arable paddock. Ammonia (NH3) volatilization measurements indicated that losses from outdoor dry sows were in the region of 11 g NH3‐N sow?1 day?1. Urine patches were identified as the major source of nitrous oxide (N2O) emissions, with N2O‐N losses estimated at less than 1% of the total N excreted. The nitrogen balance calculations indicated that N inputs to all the outdoor pig systems greatly exceeded N offtakes plus N losses, with estimated N surpluses on the CCP, IMP and BMP systems after 2 years of stocking at 576, 398 and 264 kg N ha?1, respectively, compared with 27 kg N ha?1 on the arable control. These large N surpluses are likely to exacerbate nitrate leaching losses in following seasons and make a contribution to the N requirement of future crops.  相似文献   

7.
Acetylene blockage was evaluated as a method for measuring losses of N2O + N2 from two Denchworth series clay soils. The denitrification potential in anaerobic, dark incubations at 20°C with nitrate (equivalent to 100 kg N ha?1 0–20 cm depth), maximum water holding capacity, and acetylene (1%), was equivalent to 32 ± 11 and 39 ± 6 kg N ha?1 per day for the two 0–20 cm soils and was positively correlated with carbon content (r= 0.98). After 4 days N2O was reduced to N2 in the presence of C2H2. In April 1980 following irrigation (24 mm) and applications of ammonium nitrate (70 kg N ha?1) and acetylene, the mean nitrous oxide flux from soil under permanent grass was 0.05 ± 0.01 kg N2O-N ha?1 per day for 8 days. In June 1980, the losses of nitrogen from cultivated soils under winter wheat after irrigation (36 mm) and acetylene treatment were 0.006 ± 0.002 and 0.04–0.07 ± 0.01 kg N ha?1 per day respectively before and after fertilizer application (70 kg N ha?1). The nitrous oxide flux in the presence of acetylene decreased briefly, indicating that nitrification was rate determining in drying soil.  相似文献   

8.
Abstract

To assess their impacts on net global warming, total greenhouse gas emissions (mainly CO2, N2O and CH4) from agricultural production in arable land cropping systems in the Tokachi region of Hokkaido, Japan, were estimated using life cycle inventory (LCI) analysis. The LCI data included CO2 emissions from on-farm and off-farm fossil fuel consumption, soil CO2 emissions induced by the decomposition of soil organic matter, direct and indirect N2O emissions from arable lands and CH4 uptake by soils, which were then aggregated in CO2-equivalents. Under plow-based conventional tillage (CT) cropping systems for winter wheat, sugar beet, adzuki bean, potato and cabbage, on-farm CO2 emissions from fuel-consuming operations such as tractor-based field operations, truck transportation and mechanical grain drying ranged from 0.424 Mg CO2 ha?1 year?1 for adzuki bean to 0.826 Mg CO2 ha?1 year?1 for winter wheat. Off-farm CO2 emissions resulting from the use of agricultural materials such as chemical fertilizers, biocides (pesticides and herbicides) and agricultural machines were estimated by input–output tables to range from 0.800 Mg CO2 ha?1 year?1 for winter wheat to 1.724 Mg CO2 ha?1 year?1 for sugar beet. Direct N2O emissions previously measured in an Andosol field of this region showed a positive correlation with N fertilizer application rates. These emissions, expressed in CO2-equivalents, ranged from 0.041 Mg CO2 ha?1 year?1 for potato to 0.382 Mg CO2 ha?1 year?1 for cabbage. Indirect N2O emissions resulting from N leaching and surface runoff were estimated to range from 0.069 Mg CO2 ha?1 year?1 for adzuki bean to 0.381 Mg CO2 ha?1 year?1 for cabbage. The rates of CH4 removal from the atmosphere by soil uptake were equivalent to only 0.020–0.042 Mg CO2 ha?1 year?1. From the difference in the total soil C pools (0–20 cm depth) between 1981 and 2001, annual CO2 emissions from the CT and reduced tillage (RT) soils were estimated to be 4.91 and 3.81 Mg CO2 ha?1 year?1, respectively. In total, CO2-equivalent greenhouse gas emissions under CT cropping systems in the Tokachi region of Hokkaido amounted to 6.97, 7.62, 6.44, 6.64 and 7.49 Mg CO2 ha?1 year?1 for winter wheat, sugar beet, adzuki bean, potato and cabbage production, respectively. Overall, soil-derived CO2 emissions accounted for a large proportion (64–76%) of the total greenhouse gas emissions. This illustrates that soil management practices that enhance C sequestration in soil may be an effective means to mitigate large greenhouse gas emissions from arable land cropping systems such as those in the Tokachi region of northern Japan. Under RT cropping systems, plowing after harvesting was omitted, and total greenhouse gas emissions from winter wheat, sugar beet and adzuki bean could be reduced by 18%, 4% and 18%, respectively, mainly as a result of a lower soil organic matter decomposition rate in the RT soil and a saving on the fuels used for plowing.  相似文献   

9.
To establish a national inventory of soil organic carbon (SOC) stocks and their change over time, soil was sampled in 1986, 1997 and 2009 in a Danish nation‐wide 7‐km grid and analysed for SOC content. The average SOC stock in 0–100‐cm depth soil was 142 t C ha?1, with 63, 41 and 38 t C ha?1 in the 0–25, 25–50 and 50–100 cm depths, respectively. Changes at 0–25 cm were small. During 1986–97, SOC in the 25–50‐cm layer increased in sandy soils while SOC decreased in loam soils. In the subsequent period (1997–2009), most soils showed significant losses of SOC. From 1986 to 2009, SOC at 0–100 cm decreased in loam soils and tended to increase in sandy soils. This trend is ascribed to dairy farms with grass leys being abundant on sandy soils while cereal cropping dominates on loamy soils. A statistical model including soil type, land use and management was applied separately to 0–25, 25–50 and 50–100 cm depths to pinpoint drivers for SOC change. In the 0–25 cm layer, grass leys added 0.95 t C ha?1 year?1 and autumn‐sown crops with straw incorporation added 0.40 t C ha?1 year?1. Cattle manure added 0.21 t C ha?1 year?1. Most interestingly, grass leys contributed 0.58 t C ha?1 year?1 at 25–50 cm, confirming that inventories based only on top‐soils are incomplete. We found no significant effects in 50–100 cm. Our study indicates a small annual loss of 0.2 t C ha?1 from the 0–100 cm soil layer between 1986 and 2009.  相似文献   

10.
Annual potassium (K) balances have been calculated over a 40‐year period for five field experiments located on varying parent materials (from loamy sand to clay) in south and central Sweden. Each experiment consisted of a number of K fertilizer regimes and was divided into two crop rotations, mixed arable/livestock (I) and arable only (II). Annual calculations were based on data for K inputs through manure and fertilizer, and outputs in crop removal. Plots receiving no K fertilizer showed negative K balances which ranged from 30 to 65 kg ha?1 year?1 in rotation I, compared with 10–26 kg ha?1 year?1 for rotation II. On sandy loam and clay soils, the K yield of nil K plots (rotation I) increased significantly with time during the experimental period indicating increasing release of K from soil minerals, uptake from deeper soil horizons and/or depletion of exchangeable soil K (Kex). Significant depletion of Kex in the topsoil was only found in the loamy sand indicating a K supply from internal sources in the sandy loam and clay soils. On silty clay and clay soils, a grass/clover ley K concentration of ～2% (dry weight) was maintained during the 40‐year study period on the nil K plots, but on the sandy loam, loam and loamy sand, herbage concentrations were generally less than 2% K.  相似文献   

11.
Abstract. In dairy farming systems the risk of nitrate leaching is increased by mixed rotations (pasture/arable) and the use of organic manure. We investigated the effect of four organic farming systems with different livestock densities and different types of organic manure on crop yields, nitrate leaching and N balance in an organic dairy/crop rotation (barley–grass-clover–grass-clover–barley/pea–winter wheat–fodder beet) from 1994 to 1998. Nitrate concentrations in soil water extracted by ceramic suction cups ranged from below 1 mg NO3-N l?1 in 1st year grass-clover to 20–50 mg NO3-N l?1 in the winter following barley/pea and winter wheat. Peaks of high nitrate concentrations were observed in 2nd year grass-clover, probably due to urination by grazing cattle. Nitrate leaching was affected by climatic conditions (drainage volume), livestock density and time since ploughing in of grass-clover. No difference in nitrate leaching was observed between the use of slurry alone and farmyard manure from deep litter housing in combination with slurry. Increasing the total-N input to the rotation by 40 kg N ha?1 year?1 (from 0.9 to 1.4 livestock units ha?1) only increased leaching by 6 kg NO3-N ha?1. Nitrate leaching was highest in the second winter (after winter wheat) following ploughing in of the grass-clover (61 kg NO3-N ha?1). Leaching losses were lowest in 1st year grass-clover (20 kg NO3-N ha?1). Averaged over the four years, nitrate concentration in drainage water was 57 mg l?1. Minimizing leaching losses requires improved utilization of organic N accumulated in grazed grass-clover pastures. The N balance for the crop rotation as a whole indicated that accumulation of N in soil organic matter in the fields of these systems was small.  相似文献   

12.
Evaluation of carbon dynamics is of great concern worldwide in terms of climate change and soil fertility. However, the annual CO2 flux and the effect of land management on the carbon budget are poorly understood in Sub-Saharan Africa, owing to the relative dearth of data for in situ CO2 fluxes. Here, we evaluated seasonal variations in CO2 efflux rate with hourly climate data in two dry tropical croplands in Tanzania at two sites with contrasting soil textures, viz. clayey or sandy, over four consecutive crop-cultivation periods of 40 months. We then: (1) estimated the annual CO2 flux, and (2) evaluated the effect of land management (control plot, plant residue treatment plot, fertilizer treatment plot, and plant residue and fertilizer treatment plot) on the CO2 flux and soil carbon stock at both sites. Estimated annual CO2 fluxes were 1.0–2.2 and 0.9–1.9 Mg C ha?1 yr?1 for the clayey and sandy sites, respectively. At the end of the experiment, crop cultivation had decreased the surface soil carbon stocks by 2.4 and 3.0 Mg C ha?1 (soil depth 0–15 cm) at the clayey and sandy sites, respectively. On the other hand, plant residue application (7.5 Mg C ha?1 yr?1) significantly increased the surface soil carbon stocks, i.e., 3.5–3.8 and 1.7–2.1 Mg C ha?1 (soil depth 0–15 cm) at the clayey and sandy sites, respectively, while it also increased the annual CO2 fluxes substantially, i.e., 2.5–4.0 and 2.4–3.4 Mg C ha?1 yr?1 for the clayey and sandy soils, respectively. Our results indicate that these dry tropical croplands at least may act as a carbon sink, though the efficiency of carbon accumulation was substantially lower in sandy soil (6.8–8.4%) compared to clayey soil (14.0–15.2%), possibly owing to higher carbon loss by leaching and macro-faunal activity.  相似文献   

13.
Rainfed agricultural systems in semiarid Mediterranean environments are subject to erratic but often heavy rainfall events.As an agronomic practice,fallow periods can be included even within the existing European Union common policy for crop diversification.This study aimed to quantify the effects of previous mineral fertilization on soil mineral nitrogen (Nmin) content and potential nitrate leaching during no-till fallow periods of crop rotation.The Leaching Estimation and Chemistry Model (LEAC...  相似文献   

14.
A field experiment was carried out in a semi-arid region of Iran during the 2006–2007 growing season to investigate canola seed yield as affected by nitrogen (N) and natural zeolite (Z) rates. This experiment studied N efficiency and N leaching loss in a sandy soil. Experimental treatments consisted of a factorial combination of three N levels (90, 180, and 270 kg N ha?1) and four zeolite rates (0, 3, 6, and 9 t zeolite ha?1). The result showed that the greatest seed yield (2452.3 kg ha?1) was obtained from the N270Z9 treatment whereas the control treatment (N0Z0) produced the lowest seed yield (1038.3 kg ha?1). Moreover, use of 270 kg N ha?1 without zeolite (N270Z0) led to the greatest amount of N leaching loss (144.23 kg ha?1). Zeolite application clearly reduced N leaching loss in all N rates. This justified low N-use efficiency in high N applications. More N uptake and more canola seed yield is attributed to zeolite application.  相似文献   

15.
A simple, sensitive method developed for the analysis of geostandards was used to measure the accumulation of Cd in soils from superphosphate applied annually to grass-land and arable soils for many years. Rates of application were equivalent to 33 kg P and 5 g Cd ha?1 yr?1 for 95 yr in three experiments in England and to 37 kg P and 20 g Cd ha?1 yr ?1 for 30 yr in one experiment in New Zealand. Very little Cd accumulated in the surface horizons (0–22.5cm) of either of the arable soils from England; about one-quarter of the applied Cd was detected in the sub-soil (22.5–45.0 cm) of one experiment (Broadbalk) but none in the second (Barnfield). About one-half of the applied Cd was retained in the 0–22.5 cm horizon of grassland soils from both England and New Zealand. The light (<2.2 gcm?3) organic-rich fraction of Park Grass soil from Éngland contained about three times as much Cd as the heavier, mineral-rich fraction. This suggests that when Cd is incorporated into organic matter its mobility is decreased and soil pH then has smaller effects on its mobility. Uptake of Cd by grass-clover pasture in New Zealand averaged only 0.4 g Cd ha?1 yr?1 or 2% of the amount applied.  相似文献   

16.
Nitrous oxide emission (N2O) from applied fertilizer across the different agricultural landscapes especially those of rainfed area is extremely variable (both spatially and temporally), thus posing the greatest challenge to researchers, modelers, and policy makers to accurately predict N2O emissions. Nitrous oxide emissions from a rainfed, maize-planted, black soil (Udic Mollisols) were monitored in the Harbin State Key Agroecological Experimental Station (Harbin, Heilongjiang Province, China). The four treatments were: a bare soil amended with no N (C0) or with 225?kg?N ha?1 (CN), and maize (Zea mays L.)-planted soils fertilized with no N (P0) or with 225?kg?N ha?1 (PN). Nitrous oxide emissions significantly (P?<?0.05) increased from 141?±?5?g N2O-N?ha?1 (C0) to 570?±?33?g N2O-N?ha?1 (CN) in unplanted soil, and from 209?±?29?g N2O-N?ha?1 (P0) to 884?±?45?g N2O-N?ha?1 (PN) in planted soil. Approximately 75?% of N2O emissions were from fertilizer N applied and the emission factor (EF) of applied fertilizer N as N2O in unplanted and planted soils was 0.19 and 0.30?%, respectively. The presence of maize crop significantly (P?<?0.05) increased the N2O emission by 55?% in the N-fertilized soil but not in the N-unfertilized soil. There was a significant (P?<?0.05) interaction effect of fertilization?×?maize on N2O emissions. Nitrous oxide fluxes were significantly affected by soil moisture and soil temperature (P?<?0.05), with the temperature sensitivity of 1.73–2.24, which together explained 62–76?% of seasonal variation in N2O fluxes. Our results demonstrated that N2O emissions from rainfed arable black soils in Northeast China primarily depended on the application of fertilizer N; however, the EF of fertilizer N as N2O was low, probably due to low precipitation and soil moisture.  相似文献   

17.
The aim of this study was to assess the changes in soil organic carbon (SOC) stock in relation to the carbon (C) input from nine wheat-based cropping systems and untilled grass. The SOC pool ranged from 32.1 to 49.4 Mg ha?1 at 0–20 cm and from 94 to 171 Mg ha?1 at 0–100 cm for the arable soil, while in untilled grassland, it was higher (54 and 185 Mg C ha?1, respectively). SOC stock was observed to be lower at the unfertilized 2-year rotation and higher at the 4-year rotation with manure and mineral fertilization. The study showed a winter wheat yield decrease of 176.8 kg ha?1 for a 1- Mg ha?1 SOC stock change in the 0–20-cm soil depth. The estimated C input for SOC stock maintenance was from 266 to 340 g C m?2 year?1 for winter wheat and rotations, respectively. Additional C input did not increase the SOC pool, suggesting that arable plots had a limited ability to increase SOC. These results provide guidance for the selection of management practices to improve C sequestration.  相似文献   

18.
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.  相似文献   

19.
Compost amendment to agricultural soils has been reported to reduce disease incidence, conserve soil moisture, control weeds, or improve soil fertility. Application rate and placement of compost largely depends on the proposed beneficial effects and the rate may vary from 25 to 250 Mg ha?1 (N content up to 4 percent). Application of high rates of compost with high N or P levels may result in excessive leaching of nitrate, ammonium, and phosphate into the groundwater. Leaching could be a serious concern on the east coast of Florida with its inherent high annual rainfall, sandy soils and shallow water table. In this study, five composts (sugarcane filtercake, biosolids, and mixtures of municipal solid wastes and biosolids) were applied on the surface of an Oldsmar sand soil (in 7.5 cm diameter leaching columns) at 100 Mg ha?1 rate and leached with deionized water (300 ml day?1, for five days; equivalent to 34 cm rainfall). The concentrations of NO3-N, NH4-N, and PO4-P in leachate reached as high as 246, 29, and 7 mg L?1, respectively. The amount of N and P leached accounted for 3.3-15.8 percent of total N and 0.2-2.8 percent of total P in the compost. The leaching peaks of NO3-N occurred following the application of only 300-400 ml water (equivalent to 6.8-9.1 cm rainfall).  相似文献   

20.
To study the influence of potassium (K) fertilizer rate on soil test K values, crop yield, and K-leaching in sandy soils, four long-term fertilizer experiments (0–60–120–180 kg K ha?1 a?1) were initiated in 1988 in northern Germany on farmers fields. Clay content of the plow layer was about 4%, and organic matter between 2% and 5%. Plant available soil K was estimated with the double lactate (DL) method. Small grain cereals (rye and barley) did not respond to K fertilization in the 7-year period even though the soil test value of the K-0 plots decreased from ca. 90 to ca. 30 mg KDL kg?1 within 3 years. This value remained almost constant thereafter. Crop removal (including straw) of 75 kg K ha?1 a?1 was therefore apparently supplied from nonexchangeable K fractions. Compared to the optimum, no K application reduced the yield of potato by up to 21%, and that of white sugar yield up to 10%. Maximum potato yield was obtained by annually applying 60 kg K ha?1 which resulted in a test value of 60 mg KDL kg?1 soil. Maximum potato yield was also obtained at 40 mg KDL kg?1 soil, however, with a single application of 200 kg K ha?1. Similar results were obtained with sugar beet. This indicates that for maximum yield, even for K demanding crops, it is not necessary to maintain KDL values above 40 mg K kg?1 soil throughout the entire crop rotation. Soil test values increased roughly proportional to the K fertilizer level. About 120 kg fertilizer K ha?1 a?1, markedly more than crop K removal, was required to maintain the initial KDL of 90 mg kg?1. The K concentration of the soil solution in the top soil measured after harvest was increased exponentially by K fertilizer level and so was K leaching from the plow layer into the rooted subsoil. The leached quantity increased from 22 kg K ha?1 a?1 in the plot without K application to 42.79 and 133 kg Kha?1 a?1 in plots supplied with 60, 120 and 180 kg K ha?1 a?1 respectively. Soil test values around 100 mg KDL kg?1 on sandy soils, as often found in the plow layer of farmers fields, lead to K leaching below the root zone that may exceed the critical K concentration of 12 mg K T?1 for drinking water.  相似文献   

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