Compost Source and Rate Effects on Soil Macronutrient Availability Under Saint Augustine Grass and Bermuda Grass Turf

Compost application to turf grasses can increase availability of nutrients in soil and improve growth, but can potentially lead to accumulation of macronutrients in soil and contribute to leaching and runoff losses. The objectives of this study were to investigate the influence of compost source and application rate on concentrations of plant-available macronutrients in soil over 29 months after a one-time application to saint augustine grass [Stenotaphrum secundatum (Walt.) Kuntze] and Bermuda grass [Cynodon dactylon (L.) Pers.] turf. Compost application increased soil organic C, P, Ca, and S concentrations by 3 months after addition, but further increases from 3 to 29 months were seldom observed. In contrast, NO₃-N and K levels declined while Mg levels increased slightly from 3 to 29 months. Seasonal or cyclical patterns of soil macronutrient levels were apparent, as lower concentrations were observed during dormant stages of Bermuda grass growth in winter. Initial macronutrient concentrations of compost sources strongly influenced macronutrient dynamics in surface soil, while higher application rates resulted in higher levels of P, K, Ca, Mg, but not NO₃-N and S. Higher levels of macronutrients in Bermuda grass than saint augustine grass turf suggested plant-mediated uptake and assimilation differed between turf grass species. Utilization of turf grass systems for compost application should take into account plant species composition and the related impacts of plant uptake. Macronutrient concentrations were significantly correlated with both total organic C and dissolved organic C (DOC). Formation of organic matter-cation complexes appeared to influence macronutrient dynamics in soil, and may contribute to leaching and runoff losses.     

控释尿素减施对双季稻田土壤剖面养分分布特征的影响

为探讨双季稻田控释尿素施用对养分在土壤剖面的垂直分布与迁移的影响,通过长期田间定位试验,研究比较普通尿素(U)和控释尿素(CRU)减施稻田剖面的养分累积和分布。结果表明:随着土层深度的增加,土壤全氮、NO_3~-—N、有机质、全磷、速效磷和全钾含量呈下降趋势,NH_4~+—N含量先下降后升高,速效钾含量呈上升趋势,土壤pH升高且趋于稳定。施肥会降低0—20cm土层pH和速效钾含量。与U处理相比,0—20cm土层CRU处理全氮含量提高7.72%~19.45%,且随着施N量的增加呈上升趋势;40—60cm土层CRU处理NH_4~+—N含量降低6.99%~19.23%。施用CRU可以有效降低土层NH_4~+—N向下淋溶,提高0—40cm土层全氮和NO_3~-—N含量,避免土壤N素流失。施用CRU对不同深度土层有机质、速效磷、全磷、速效钾、全钾和pH的影响不显著,但减量过大会导致有机质降低。CRU减量10%~20%处理显著提高双季稻成熟期N、P、K的吸收量。相关分析表明,不同用量控释尿素处理早、晚稻成熟期N、P、K吸收量与籽粒产量均呈显著正相关。总之,CRU处理有效地控制N素向下淋溶,减少因N肥施用带来的潜在面源污染,而CRU减施可更好地维持和提高土壤的养分水平和肥力,促进养分累积,实现生态与经济效益的双赢。     

Temporal dynamics of soil nitrate-N after termination of forage phases in corn-forage rotation

 Efficient N-fertiliser management during the corn (Zea mays L.) phase in corn-forage rotation requires information on temporal dynamics of N release from forage biomass. The influence of forage phase, in corn-forage rotation, and no- versus conventional-till on (1) in situ temporal dynamics of soil nitrate-N (NO₃-N) during corn phase and (2) corn grain yield was investigated in this study. The data used were collected from a crop rotation (corn-forage) experiment, with superimposed tillage treatments, established on a silt loam soil in 1988 and continued until 1994. The cropping treatments were continuous conventionally cultivated (CT) corn, rotations involving corn and forages (alfalfa, Medicago sativa L.; and bromegrass, Bromus inermis L.) and continuous minimally tilled corn with under-seeded red clover (Trifolium pratense L.). The forages were grown for 6 years and corn was re-introduced in these plots under no- and conventional-till systems. Soil NO₃-N in the top 30 cm depth, determined six times during the corn phase, was significantly influenced by previous forage species and tillage system. Regression analysis indicated soil NO₃-N under continuous CT corn did not show significant temporal changes. In the rotations, soil NO₃-N after tillage or herbicide treatment, i.e. in no-till, increased with time until 45 days after tillage (DAT), reached a plateau between 45 and 65 DAT, and then decreased with time. During the plateau, soil NO₃-N in rotation plots ranged from 17 to 33 mg kg^–1 compared to 15.7 mg kg^–1 in the continuous CT corn. Tillage increased soil NO₃-N concentration in alfalfa plots whereas an opposite trend existed in the bromegrass plots. Soil NO₃-N in the rotation plots increased at rates ranging from 0.71 to 1.63 mg kg^–1 day^–1. The interaction involving forage species and the temporal dynamics of soil NO₃-N accounted for 68–77% of variability in corn grain yield. Received: 14 July 1998     

Nutritional changes in petiole sap over space and time in a tomato crop greenhouse

The aims of this trial were to determine the spatial and temporal variability of the nutrients in petiole sap in a tomato crop under greenhouse and to determine the number of sub-samples for a representative sample. The experiment consisted of the selection of 20 sampling points. Petiole of fully expanded leaf was collected weekly in order to determine Cl, NO₃-N, H₂PO₄-P, SO₄-S, Na, K, Ca and Mg concentrations. Our results showed that variations of NO₃-N, Na, Ca and K concentrations in sap were affected by the spatial distribution, whereas SO₄-S and Mg concentrations in sap were affected by their temporal distribution. The spatial variability of our experiment could be related to radiation, yield and antagonism between nutrients, whereas the time variability could be related to the phenological stage of the plant and the antagonism between nutrients. The suggested number of petiole sub-sample ranging from 25 to 113 depending on nutrient.     

Responses of residual and recommended N,P, K,S nutrients and crops to six annual soil test-based fertilizer rates and seeding systems

Responses of residual and recommended nitrogen (N), phosphorus (P), potassium (K), sulfur (S) nutrient amounts and crops (yield, emergence, and height) to 0, 60, 100, and 140% soil test-based fertilizer rate applications on the same plots for six years under minimum tillage and direct seeding systems were assessed. Higher fertilizer rates increased residual nitrate (NO₃)-N, extractable K, and sulfate (SO₄)-S amounts after a low crop yield year, particularly NO₃-N, without temporal trend. Increase in residual available P level at higher fertilizer rates showed a positive temporal trend. Lower N, P, and S fertilizer rates were recommended to crops after higher residual NO₃-N, available P, and SO₄-S levels. Crops effectively used the residual nutrients. Compared to 0%, the relative seed yields at 60, 100, and 140% rates increased with years of fertilization. There were no clear responses of measured soil and crop parameters to seeding systems. Testing residual nutrients can optimize fertilizer use and crop yields.     

Relationship between Soil Temperature and N Release in Organic and Conventionally Managed Vineyards

Soil temperature is a very easily measured parameter that influences nutrient availability in vineyards. We monitored soil temperature and plant-available nitrogen (N) in a study evaluating the potential of legumes as an interrow cover crop to supply N to Concord grape (Vitis labruscana Baily). Nitrogen sources used were hairy vetch (Vicia villosa subsp. villosa L.) and yellow sweet clover [Melilotus officinalis (L.) Lam] as green manure sources and either blood meal (in a certified organic vineyard) or urea (in a conventional vineyard) as soluble sources. Plant-available N was measured both continuously using ion exchange membranes (PRS^TM) and point in time by soil sampling at regular intervals; both were analyzed for nitrate (NO₃) N and ammonium (NH₄) N, although negligible concentrations of NH₄-N were detected. PRS NO₃-N concentration varied by treatments because of differences in the chemical composition of the N source. Soil NO₃-N concentration reached a peak between 520 and 550 degree-days with no significant differences by treatment or site. These findings are similar to results from incubation and field mineralization studies of organic amendments and suggest that N availability from organic sources in vineyards can be predicted using a degree-day-type model.     

Assessment of Ionic Interferences to Nitrate and Potassium Analyses with Ion-Selective Electrodes

Ion-selective electrodes (ISEs) are simple tools used for rapid measurement of nitrate nitrogen (NO₃-N) and potassium (K) concentrations in plant sap. With the development of best management practices (BMPs), interest exists in using ISEs for soil leachate and soil and fertilizer solutions. Nitrate N and K concentrations in the 0 to 10,000 mg L^–1 ISE working range were measured in diluted solutions of common salts to assess ionic interference of calcium (Ca²⁺), ammonium (NH₄ ⁺), chloride (Cl^–), and sulfate (SO₄ ^2–). The effects of meter (replication) were unexpectedly significant in one out of three ranges for NO₃-N and K (P values of 0.50, 0.72, and 0.01 for NO₃-N and 0.99, 0.01, and 0.74 for K, for the 0–100, 100–1,000 and 1,000–10,000 mg L^–1 ranges, respectively). The responses of calculated NO₃-N and K concentrations to measured NO₃-N and K concentrations were linear, but slopes ranged from 0.85 to 1.54, from 0.24 to 2.72, and from 0.93 to 5.48 for NO₃-N and from 0.80 to 1.01, from 0.71 to 1.39, and from 0.93 to 2.21 for K for the 0–100, 100–1,000, and 1,000–10,000 mg L^–1 measuring ranges, respectively. All slopes were significantly different from zero, and several were significantly different from each other and the 1:1 line. Pairwise slope comparisons conducted with covariance analysis showed that SO₄ ^2– alone interfered with NO₃-N measurements at concentrations ranging from 34 to 171 mg L^–1, which was less than the manufacturer's information, and by its presence in combination with K⁺, NH₄ ⁺, Ca²⁺, and Cl^– within the medium and high concentration ranges. Potassium measurements were not subject to interference from the ions tested for all three concentration ranges. These results highlight the importance of using quality assurance / quality control (QA/QC) samples in the set of unknown samples to detect inacceptable departure from linearity in routine analysis. The increase in measurement variability from one range to the next showed the importance of keeping measurements within a single concentration range by using dilutions. Hence, ISEs may be used for field measurements of NO₃-N and K concentrations in soil leachate as well as soil and nutrient solutions and are therefore a practical BMP tool. However, ISEs should not be used as substitutes for the laboratory methods when official measurements are needed.     

Field and Laboratory Evaluation of the Cardy Nitrate-Nitrogen Meter for Measuring Soil Solution Nitrate Nitrogen in Hawaiian Soils

The estimation of plant-available nitrate nitrogen (NO₃-N) is essential for any nutrient-management plan but can be time-consuming and expensive. However, the efficacy of rapid methods to determine soil NO₃-N levels designed for grower use has received mixed reviews in the literature. Therefore, the objectives of this study were to (1) evaluate the Cardy electrode-based meter for measuring soil solution NO₃-N concentrations under a perennial peanut living mulch in two mixed orchard systems on O'ahu and (2) determine the influence of soil type on measurement accuracy and precision under laboratory conditions. To achieve the first objective, 24 lysimeters were installed 15–30 cm deep at each of two fruit tree orchards with different soils and climate on Oahu island. For the second objective, a replicated column study was conducted, in which NO₃-N solutions of varied concentrations were leached through three representative agricultural soils (Wahiawa, Loleka'a, and Waialua series). Field soil solution and column leachate were analyzed using the portable electrode-based meter and a standard laboratory colorimetric method. In the field samples, soil solution NO₃-N ranged from <1 to 110 mg/L, and there was a strong correlation (r²?=?0.92) between the portable meter and colorimetric values. Similarly, a strong correlation between the Cardy meter and the laboratory methods was observed in the column study, although r ² values varied with soil type. The data suggest that the Cardy meter can be used to rapidly and accurately measure soil solution NO₃-N, if its concentrations are relatively high and concentrations of interfering ions such as chloride (Cl^?) are low. Overall, the primary value of this rapid method may be in estimating relative changes in soil nitrate in response to nutrient management at a single site.     

Portable soil test laboratory results compared to standard soil test values

Abstract

Results from a commercially available portable soil test laboratory were compared to standard soil test procedures used by a public soil testing laboratory. Standard soil tests examined were water extracted NO₃‐N, pH, Acid‐P, NaHCO₃‐P, and ammonium acetate extracted K. Approximately 35 to 55 different soils were used to compare methods for each soil test. Linear regression equations between the portable laboratory soil test values and those from the standard procedures were developed. The r² values for NO₃‐N, pH, Acid‐P, NaHCO₃‐P, and K were 0.970, 0.891, 0.734, 0.742, and 0.887, respectively. The coefficient of variability values for NO₃‐N, pH, Acid‐P, NaHCO₃‐P, and K were 10, 1, 13, 15, and 6%, respectively for the portable laboratory, and 9, 2, 8, 9, and 5%, respectively for the public soil testing laboratory. Multiple regression was used to relate soil properties to soil test results. The R2 values for NO3‐N, pH, Acid‐P, NaHCO₃‐P, and K were 0.970, 0.911, 0.860, 0.940, and 0.936, respectively.     

Land-Use Effect on Selected Soil Quality Parameters

Land use is a key factor that affects soil quality. The purpose of the present study was to investigate changes of selected soil chemical properties related to soil function under different land uses. Five experimental sites arranged in a complete randomized blocks located within the Kalloni watershed (Lesvos Island, Greece) corresponding to different land uses (Pinus brutia forest, brushwood pasture, rain-fed olive grove, wheat, and maize) were compared for soil pH, electrical conductivity (EC), total nitrogen (N), nitrate N (NO₃-N), Olsen phosphorus (P), and organic matter. Soil nitrate and P concentration were in the order corn > wheat > olive > pasture > forest. Soil EC and NO₃-N showed significant within-year variability only in the corn and wheat systems. Corn and wheat had the lowest soil organic-matter content followed the order forest > pasture > olive grove = wheat = corn. However, total N did not significantly differ among land uses.     

Phosphorus uptake of maize as affected by ammonium and nitrate nitrogen - Measurements and model calculations -

Phosphorus uptake is often enhanced by ammonium compared to nitrate nitrogen nutrition of plants. A decrease of pH at the soil-root interface is generally assumed as the cause. However, an alteration of root growth and the mobilization of P by processes other than net release of protons induced by the source of nitrogen may also be considered. To study these alternatives a pot experiment was conducted with maize using a fossil Oxisol high in Fe/Al-P with low soil solution P concentration. Three levels of phosphate (0, 50, 200 mg P kg^?1) in combination with either ammonium or nitrate nitrogen (100 mg N kg^?1) were applied. Plants were harvested 7 and 21 d after sowing, P uptake measured and root and shoot growth determined. To assess the importance of factors involved in the P transfer from soil into plants, calculations were made using a model of Barber and Claassen. In the treatments with no and low P supply NH₄-N compared to NO₃-N nutrition increased the growth of the plants by 25 % and their shoot P content by 38 % while their root growth increased by 6 % only. The rhizosphere pH decreased in the NH₄-N treatments by 0.1 to 0.6 units as compared to the bulk soil while in the NO₃-N treatments it increased by 0.1 to 0.5 units. These pH changes had a minor influence on P uptake only, as was demonstrated by artificially altering the soil pH to 4.7 and 6.3 respectively. At the same rhizosphere pH, however, P influx was doubled by the application of NH₄-compared to NO₃-N. It is concluded that in this soil the enhancement of P uptake of maize plants after ammonium application cannot be attributed to the acidification of the rhizosphere but to effects mobilizing soil phosphate or increasing P uptake efficiency of roots. Model calculation showed that these effects accounted for 53 % of the P influx per unit root length in the NO₃-N and 72 % in the NH₄-N supplied plants if no P was applied. With high P application the respective figures were only 18 and 19%.     

Effects of enhanced supplies of nitrogen and sulphur on rhizosphere and soil chemistry in a Norway spruce stand in SW Sweden

Rhizophere and bulk soil chemistry were investigated in a Norway spruce stand in SW Sweden. The rhizosphere and bulk soil chemistry in water extracts in control plots (C) and plots repeatedly treated with ammonium sulphate (NS) were compared. Treatment regime was started in 1988. Cylindrical core samples of the LFH-layer and mineral soil layers were collected in 1992 and used for water extract analyses. Samples of soil from LFH-layer and mineral soil layers were taken in 1991 and 1993 for determination of CEC and base saturation. Soil pH and NH₄-N, NO₃-N and SO₄-S, Al, Ca, K and Mg concentrations in water extracts were measured for rhizosphere and bulk soils. The pH-values of bulk and rhizosphere soils in NS plots decreased compared with those in control plots, whereas concentrations of NH₄-N, NO₃-N, SO₄-S, base cations and Al in water extract increased. In both bulk and rhizosphere soils the concentration of NH₄-N was much higher than that of NO₃-N. A significant difference in the pH and Mg concentration of bulk and rhizosphere soil between the treated and control plots was found only in the 0–10 cm layer. For all layers, there was a significant difference in NH₄-N concentrations in the bulk and rhizosphere soil between the NS treatment and control plots. Concentrations of exchangeable base cations and the base saturation level in the LFH-layer decreased in the NS plots. The concentration of extractable SO₄-S increased in the NS plots. The NS treatment enhanced the amount of litter in L-layer, owing to increases in needle biomass and litterfall but led to losses of base cations, mainly K and Mg, from LFH-layer. It was concluded that the NS treatment displaced cations from exchangeable sites in the LFH-layer leading to higher concentrations of these elements in both rhizosphere and bulk soil.     

黄河三角洲典型潮滩湿地土壤硝态氮和铵态氮的空间分布特征

运用地统计学方法研究了黄河口滨岸潮滩湿地土壤中硝态氮和铵态氮的空间分布格局。结果表明,潮滩湿地土壤NO3--N和NH4+-N的水平变异性在不同土层差异较大,较高的水平变异性主要与其在潮滩湿地良好水分条件下较为活跃的物理运移特性有关;潮滩湿地表层土壤NO3--N的水平分布具有明显的空间结构,符合高斯模型,并具有中等程度的空间相关性;自然结构因素在引起NO3--N空间异质性中的贡献占优,随机因素的影响相对较小;表层土壤NO3--N的空间变异性以向低潮滩延伸且受潮汐涨落影响较大的方向最大;潮滩湿地表层土壤的NO3--N具有明显的空间分布格局,表现出向低潮滩延伸方向形成明显斑块低值区,边缘则形成斑块高值区的特征。微地貌特征和潮汐微域物理扰动强度是导致空间异质性的两个重要随机因素,而水盐条件、土壤类型和潮汐物理扰动是3个重要结构因素。     

华北山前平原农田土壤硝态氮淋失与调控研究

本文依托中国科学院栾城农业生态系统试验站小麦-玉米一年两熟长期定位试验, 应用土钻取土和土壤溶液取样器取水的方法, 研究了不同农田管理措施下土壤硝态氮的累积变化, 计算了不同氮肥处理通过根系吸收层的硝态氮淋失通量。结果表明, 小麦-玉米生长季土壤硝态氮累积量和淋失量随着施氮量的增加显著增加, 相同氮肥水平下增施磷、钾肥增加了作物的收获氮量, 施磷肥增加的作物收获氮量最高可达123kg·hm^-2·a^-1, 施钾肥增加的作物收获氮量最高为31 kg·hm^-2·a^-1。不同灌溉水平下0~400 cm 土体累积硝态氮随着灌溉量的增加而降低, 控制灌溉(小麦季不灌水, 玉米季灌溉1 水)、非充分灌溉(小麦季灌溉2~3 水, 玉米季按需灌溉)、充分灌溉(小麦季灌溉4~5 水, 玉米季按需灌溉)各处理剖面累积硝态氮量分别为1 698 kg·hm^-2、1148 kg·hm^-2 和961 kg·hm^-2。与非充分灌溉和充分灌溉处理相比, 控制灌溉在100~200 cm 土层硝态氮累积量显著高于其他层次, 2003~2005 年间控制灌溉剖面增加的硝态氮量占施肥总量的23%; 非充分灌溉处理剖面增加的硝态氮量占施肥总量的22%; 充分灌溉处理剖面增加的硝态氮量占施肥总量的47%。免耕措施降低了作物产量, 影响土壤水的运移, 增加了硝态氮的淋失风险。根据作物所需降低氮素投入(N 200 kg·hm^-2·a^-1), 增施磷、钾肥, 控制灌溉量是减少华北山前平原地区硝态氮淋失, 保护地下水的有效措施。     

Nitrate nitrogen in the soil profile and drainage water as influenced by manure and mineral fertilizer application in a Barley–Carrot production system

Nitrate-N (NO₃ ^?-N) is a ubiquitous pollutant in both surface and groundwater in many agro-ecosystems. This has elicited a concerted effort to identify management strategies that mitigate NO₃ ^?–N pollution, without compromising crop yield. This study was conducted on a field site located at the Bio-Environmental Engineering Centre (BEEC) in Truro, NS, Canada during 1999 and 2000. The site has been used since 1997 to investigate the relative effect of inorganic versus organic fertilizer (liquid hog manure; LHM) applied at rates (70 kg N ha^?1) on NO₃ ^?-N leaching from a carrot rotation system. NO₃ ^?-N concentrations were monitored in both the soil profile and in tile drainage effluents from eight treatment plots. The LHM treatment elicited significantly (P < 0.01) higher soil NO₃ ^?-N concentrations than inorganic fertilizer (IF) in June and October during 1999, but not 2000. The sampling date and soil depth were significant in most cases. Annual flow weighted averages (FWA) of NO₃ ^?-N in drainage water were generally greater for plots receiving LHM (15.4 and 10.5 mg L^?1 for 1999 and 2000, respectively), when compared to IF (8.9 and 6.0 mg L^?1 for 1999 and 2000, respectively), but the difference was significant (P < 0.05) only in 1999. Maximum NO₃ ^?-N concentrations in drainage water were similar for both treatments, while the LHM treatment had a significantly higher percentage of samples that were > 10 mg L^?1. The total NO₃ ^?-N load was greater for the LHM treatment when compared to the IF treatment in 1999. Barley and carrot yields were unaffected by treatment applications.     

Evaluating Nutrient Availability in Semi-arid Soils with Resin Capsules and Conventional Soil Tests,II: Field Studies

Commonly used soil analyses and resin capsules are employed to assess nutrient status in agriculture soils, but their validity in semi-arid ecosystems is unknown. Field studies with six rates of nitrogen (N) and phosphorus (P) application were established on crested wheat stands in both Rush Valley and Skull Valley, Utah. Resin capsule and conventional soil tests for nitrate (NO₃)-N, ammonium (NH₄)-N, and P were administered, and plant nutrient status was examined. Resin capsules were removed and replaced, and soil samples were taken every 90 d for 1 year. Concentration of P in resin capsules was not related to P rate but sodium bicarbonate (NaHCO₃)-extracted P was, and resin NH₄-N, resin NO₃-N, potassium chloride (KCl)–extracted NO₃-N and KCl-extracted NH₄-N were all related to N rate. Only KCl-extracted NO₃-N and NH₄-N levels related to plant tissue N. Overall, traditional soil tests are more effective than resin capsules in semi-arid field conditions, but resin capsules have potential for use in N assessment.     

Suspending Nitrogen Fertilization Reduces Residual Soil Nitrates in Dryland Cotton

Nitrogen (N) fertilizer use in cotton (Gossypium hirsutum L.) production is a potential source of nitrate (NO₃ ^?) contamination of soils, groundwater, and streams. The McConnell–Mitchell plots, a long-term study of cotton responses to N-fertilization and irrigation methods, were utilized to determine the NO₃ ^?-N in soil cropped to continuous cotton. The McConnell–Mitchell plots had a split-block experiential design. The main blocks of this test were irrigation methods. Each block of plots was irrigated using a single irrigation method for the entirety of the testing. Nitrogen fertilization rates were tested within each irrigation block. The soil NO₃ ^?-N content of two irrigation blocks, furrow flow (FI) and center pivot (CP), were compared to the dryland (DL) control block. Nitrogen treatments tested within each irrigation block ranged from 0 to 168.0 kg N ha^?1 in 33.6-kg N ha^?1 increments. Nitrogen treatments were tested for 18 years (1982 through 1999), discontinued for 4 years (2000 through 2003), and resumed in 2004. Soil samples were taken in the early spring (2000 and 2004) to a depth of 1.50 m in 0.15 m increments and analyzed for NO₃ ^?-N. Soil samples taken in 2004 were prior to any fertilization treatment. Irrigation method was found to influence the distribution of soil NO₃ ^?-N. Little accumulation of soil NO₃ ^?-N was observed in either irrigation block or under dryland production when N rates were less than 67.2 kg N ha^?1. Distribution of soil NO₃ ^?-N in the FI block was significantly different with sample depth and N treatment but not the interaction of depth and treatment in both 2000 and 2004. Presumably, the small and close values of the means and the greater variability of interactions compared to main effects precluded significant interactions. Differences in soil NO₃ ^?-N in the FI block after suspending N treatments for 4 years were similar to those found in 2000, although the soil NO₃ ^?-N was generally depleted in 2004 compared to 2000. The distribution of soil NO₃ ^?-N in the CP-irrigated block was dependent on the interaction of sample depth with N treatment in both 2000 and 2004. Soil NO₃ ^?-N values and differences tended to be too small to be of discernable or practical importance under CP irrigation. The distribution of soil NO₃ ^?-N in the DL block was dependent on the interaction of sample depth with N treatment in 2000 and 2004. Soil NO₃ ^?-N was minimal in the three lowest N treatments (0, 33.6, and 67.2 kg N ha^?1) in 2000. Greatest amounts of soil NO₃ ^?-N were found in conjunction with the 134.4 and 168.0 kg N ha^?1 treatments both years. Depletion of soil NO₃ ^?-N was evident in the surface 0.45 m of the 100.8, 134.4, and 168.0 kg N ha^?1 treatments under DL conditions in 2004.     

Soil nitrate-nitrogen in forested versus non-forested ecosystems in a mixed-use watershed

In tracking nutrients that enter the Gulf of Mexico via the Suwannee Basin, a disproportionate amount of the nitrate-nitrogen (NO₃-N) has been shown to originate in the Santa Fe River Watershed (SFRW). This study investigated soil NO₃-N distributions across the range of land-use and soil order combinations that exist in the SFRW with a focus on comparing NO₃-N levels in forested versus non-forested land-uses. The SFRW consists of 52% forested land-uses (i.e. pine plantation, forest regeneration, upland forest, and forested wetland), 47% non-forested land-uses (i.e. agriculture, rangeland, and urban), and 1% water. Soil samples were collected from four depth intervals (0-30, 30-60, 60-120, 120-180 cm) at 101 to 141 sites with a stratified-random design in six sampling events (Sept. 2003, Jan. 2004, May 2004, Jan. 2005, May 2005, and Sept. 2005). No samples were collected in Sept. 2004 due to flooding associated with two hurricanes. Nitrate-nitrogen was significantly lower in forested than non-forested land-uses across all sampling events, depth intervals, and for profile average data. Within the non-forested land-use category, NO₃-N levels were highest in row crop agriculture and improved pasture sites. In terms of soil order, NO₃-N values were generally highest in Ultisols and Spodosols, but soil order explained less of the variation in the NO₃-N data than did land-use or sampling date. Nitrate-N concentrations were considerably altered by Hurricanes Frances and Jeanne which passed over the SFRW in late summer of 2004. In the post-hurricane sampling events, NO₃-N was significantly lower in both forested and non-forested sites. A year later, however, NO₃-N concentrations in forested sites remained quite low, while concentrations in non-forested sites had begun to increase.     

旱作地区长期小麦连作和苜蓿连作土壤剖面的矿质氮研究

对不同施肥条件下23年小麦连作地和苜蓿连作地土壤矿质氮分布和累积进行研究,探讨种植浅根系和深根系植物对硝态氮淋溶的影响。结果表明,不施肥(CK)和单施磷(P)肥,小麦和苜蓿连作地土壤硝态氮主要集中在0—60 cm土层,0—60 cm土层以下硝态氮含量变化稳定并小于2 mg/kg。氮肥、磷肥和有机肥配施(NPM)时,小麦连作地土壤硝态氮累积在20—100 cm和140—320 cm土层,年累积速率可达42.12 kg/(hm2.a);苜蓿连作土壤硝态氮主要集中在0—60 cm土层,仅在200—300 cm土层出现轻微累积,年累积速率仅为1.01 kg/(hm2.a)。在不施肥和单施磷肥下,种植小麦或苜蓿对土壤硝态氮残留量影响不显著,而氮、磷和有机肥配施时,小麦连作地土壤硝态氮残留量迅速增加,并与不施肥、单施磷肥处理有显著差异;苜蓿连作地土壤硝态氮残留量虽有少量增加,但与不施肥、单施磷肥处理无显著差异。不施肥、单施磷肥和氮、磷和有机肥配施,小麦连作、苜蓿连作地土壤剖面铵态氮含量主要在10—20 mg/kg之间波动,在土壤剖面无明显的累积现象,铵态氮残留量受施肥和作物种类的影响不显著。     

Clinoptilolite Zeolite Influence on Nitrogen in a Manure-Amended Sandy Agricultural Soil

Zeolite minerals may improve nitrogen availability to plants in soil and reduce losses to the environment. A study was conducted to determine the influence of clinoptilolite (CL) on nitrogen (N) mineralization from solid dairy manure (224 kg N ha^?1) in a sandy soil. Clinoptilolite was added to soil at six rates (0 to 44.8 Mg CL ha^?1), each sampled during 11 sampling dates over a year. Over time, nitrate (NO₃)-N increased, ammonium (NH₄)-N decreased, but total inorganic N increased. Clinoptilolite did not influence the nitrification rates of initial manure NH₄-N or mineralization of organic N (ON) over time. It is possible that adsorption of manure-derived potassium (K) outcompeted the NH₄-N for CL exchange sites. The ON concentration was constant up to 84 days and then decreased by approximately 18% over the remaining time of the study across all treatments. Clinoptilolite use in this sandy soil did not alter mineralization of N from dairy manure.