Mineralization of nitrogen in fertilizer-acidified lime-amended soils

Summary The application of NH _inf4 ^su+ -based fertilizers to soils slowly lowers soil pH, which in turn decreases nitrification rates. Under these conditions nitrification and N mineralization may be reduced. We therefore investigated the impact of liming fertilizer-acidified soils on nitrification and N mineralization. Soil samples were collected in the spring of 1987 from a field experiment, initiated in 1980, investigating N, tillage, and residue management under continuous corn (Zea mays L.). The pH values (CaCl₂) in the surface soil originally ranged from 6.0 to 6.5. After 6 years the N fertilizer and tillage treatments had reduced the soil pH to values that ranged between 3.7 and 6.2. Incubation treatments included two liming rates (unlimed or SMP-determined lime requirement), two ¹⁵N-labeled fertilizer rates (0 or 20 g N m^-2), and three replicates. Field-moist soil was mixed with lime and packed by original depth into columns. Labeled-¹⁵N ammonium sulfate in solution was surface-applied and columns were leached with 1.5 pore volumes of deionized water every 7 days over a 70-day period. Nitrification occurred in all pH treatments, suggesting that a ferilizer-acidified soil must contain a low-pH tolerant nitrifier population. Liming increased soil pH values (CaCl₂) from 3.7 to 6.2, and increased by 10% (1.5 g N m^-2) the amount of soil-derived NO₃ ^--N that moved through the columns. This increase was the result of enhanced movement of soil-derived NO₃ ^--N through the columns during the first 14 days of incubation. After the initial 14-day period, the limed and unlimed treatments had similar amounts of soil N leaching through the soil columns. Lime increased the nitrification rates and stimulated the early movement of fertilizer-derived NO₃ ^--N through the soil.     

Nitrate Mobility in Variable-Charge Tropical Soils

ABSTRACT

Nitrate (NO₃ ^–-N) leaching in tropical soils, which are more weathered, is influenced by their mineralogical, physical, and chemical characteristics. Thus, the present study aimed to evaluate the effect of the variation of net electrical charge on the mobility of nitrate, applied as potassium nitrate (KNO₃) or calcium nitrate (Ca(NO₃)₂), in samples from A and B horizons of three Red-Yellow Latosols (Oxisols), with different mineralogical and textural characteristics. Hydrochloric acid (HCl) or sodium hydroxide (NaOH) volumes were added to previously sterilized soil samples in order to condition five hydrogen potential (pH) values, obtaining different net electrical charges. The experiment was carried out with leaching columns under laboratory conditions. The soil columns were percolated with solutions of KNO₃ or Ca(NO₃)₂ or water (control). An increase in positive net charges was significant and varied according to the soil and percolating solution; in general, it resulted in an increase of up to 50% in nitrate adsorption in some soils. Larger amounts of adsorbed nitrate were observed in the columns filled with the B horizon of the clayey gibbsitic Red-Yellow Latosol, showing adsorption of 85% for a positive net charge of 2 cmol_c kg^?1. Regarding kaolinitic soils, lower adsorption was observed in the medium-textured kaolinitic Red-Yellow Latosol, which had lower clay content and positive net charge. Application of Ca(NO₃)₂, as a percolating solution, increased nitrate adsorption compared to the application of KNO₃. This effect may be attributed to the increase in positive net charge promoted by calcium (Ca²⁺), being more evident for the highest negative net charges.     

Residual Soil Nitrate: A Comparison between Air-Dried and Field-Moist Soil Samples

In the framework of the European nitrate directive (91/676/EEG), losses of nitrate (NO₃)– nitrogen (N) to both surface and groundwater are limited to 50 mg/l. Because the residual NO₃-N in the soil profile after harvest is considered the main determinant of nitrate leaching during wintertime, the Flemish government imposed a limit value of 90 kg NO₃-N ha^?1 up to a soil depth of 90 cm between 1 October and 15 November. This study compared two different soil sample preparation methodologies. When samples were analyzed immediately upon arrival, no differences in NO₃-N concentration were observed. However, although field-moist samples are maintained at 4 °C, nitrification is not completely stopped, as indicated by the increased NO₃-N concentration in field-moist samples 10 days after storage at 4 °C . In contrast, nitrification in air-dried samples is stopped during the oven drying when 40 °C is reached. Moreover, the reproducibility was significantly greater in air-dried samples as compared to field-moist samples.     

Nitrification,acidification, and nitrogen leaching from subtropical cropland soils as affected by rice straw-based biochar: laboratory incubation and column leaching studies

Purpose

Few studies have examined the effects of biochar on nitrification of ammonium-based fertilizer in acidic arable soils, which contributes to NO₃ ^? leaching and soil acidification.

Materials and methods

We conducted a 42-day aerobic incubation and a 119-day weekly leaching experiment to investigate nitrification, N leaching, and soil acidification in two subtropical soils to which 300 mg N kg^?1 ammonium sulfate or urea and 1 or 5 wt% rice straw biochar were applied.

Results and discussion

During aerobic incubation, NO₃ ^? accumulation was enhanced by applying biochar in increasing amounts from 1 to 5 wt%. As a result, pH decreased in the two soils from the original levels. Under leaching conditions, biochar did not increase NO₃ ^?, but 5 wt% biochar addition did reduce N leaching compared to that in soils treated with only N. Consistently, lower amounts of added N were recovered from the incubation (KCl-extractable N) and leaching (leaching plus KCl-extractable N) experiments following 5 wt% biochar application compared to soils treated with only N.

Conclusions

Incorporating biochar into acidic arable soils accelerates nitrification and thus weakens the liming effects of biochar. The enhanced nitrification does not necessarily increase NO₃ ^? leaching. Rather, biochar reduces overall N leaching due to both improved N adsorption and increased unaccounted-for N (immobilization and possible gaseous losses). Further studies are necessary to assess the effects of biochar (when used as an addition to soil) on N.     

氮肥配施生化抑制剂对黄泥田土壤钾素淋溶特征的影响

中国南方黄泥田土壤中养分淋失严重,尤其是氮(N)和钾(K),不仅造成资源浪费和潜在环境威胁,还严重制约作物的可持续生产。采用室内土柱模拟培养,研究尿素(U)和尿素硝铵(UAN)中单独添加脲酶抑制剂N-丁基硫代磷酰三胺(NBPT)和硝化抑制剂2-氯-6-(三氯甲基)吡啶(CP),及两者配合施用对黄泥田土壤中K素淋溶特征的影响,探讨提高黄泥田供钾能力的施肥技术。不同氮肥种类淋溶液中,K~+平均浓度大小表现为UAN处理(103.0 mg·kg~(-1))高于U处理(93.9 mg·kg~(-1)),且抑制剂处理间存在明显差异。培养结束时(第72 d),UAN处理K~+淋失量较U处理高6.7%。U各处理淋溶液中K~+累积量大小表现为UU+NBPTU+NBPT+CPU+CPCK,其中U+NBPT、U+CP和U+NBPT+CP处理较U处理分别降低8.7%、20.2%和14.9%;UAN各处理淋溶液中K~+累积量表现为UANUAN+NBPTUAN+NBPT+CPUAN+CPCK,其中UAN+NBPT、UAN+CP和UAN+NBPT+CP处理较UAN处理分别降低6.0%、13.8%和9.2%。不同施肥处理K~+淋溶率表现为UANUAN+NBPTUUAN+NBPT+CPUAN+CPU+NBPTU+NBPT+CPU+CP。培养中期(第36 d),U和UAN处理肥际微域中土壤速效钾含量显著降低,而添加CP处理有效维持土壤中较高的速效钾含量。与单施NBPT相比,配施CP可以减少黄泥田土壤中NO_3~-淋溶,增加土壤晶格对K~+的固定,减轻K~+淋溶风险,有效时间超过72 d。对各处理淋溶液中K~+累积量(y)随NO_3~-累积量(x)的变化进行拟合,其中以线性方程(y=ax+b)和Elovich方程(y=alnx+b)的拟合度最高,且抑制剂处理间a、b值均存在明显差异。总之,在黄泥田土壤中单施CP,或与NBPT配施可以有效增加K~+吸附,降低土壤中K~+淋溶损失,减轻养分淋失风险,提高肥料利用率。     

Conservation of mineral nitrogen in restored soils at opencast coal mine sites: II. The effects of inhibition of nitrification and organic amendments on nitrogen losses and soil microbial biomass

Soils stored in stockpiles during opencast mining operations accumulate significant quantities of ammonium (of the order of 200 μg NH₄⁺-N g^?1 soil) within the predominantly anaerobic cores of mounds. Upon stockpile dismantling and land restoration, this NH⁺₄-N is rapidly oxidized to NO^?₃-N, which is readily lost from newly restored soil ecosystems by leaching and denitrification. Experiments were set up to examine how these significant reserves of mineral N might be conserved in such situations. Application of the nitrification inhibitor dicyandiamide was successful in minimizing NO₃^?-N lost by leaching, though large concentrations of NH₄⁺-N were detected in drainage waters. Straw incorporation decreased nitrate leaching by up to 40%; biomass C was some 40% greater in straw-amended than in unamended soils after 14 weeks, though biomass N was similar in both. Addition of nitrogen-free organic materials (glucose, starch and cellulose) produced different results, with glucose amendment showing the greatest reduction in nitrate leaching in the short term (due to an apparent stimulation of denitrification) whereas addition of cellulose resulted in the most effective conservation of nitrogen over 14 weeks; this was due, at least in part, to uptake of mineral N by the soil microbial biomass.     

灌溉施用氮肥后氮素在土壤中的转化及淋失状况: 土柱模拟研究

A soil column method was used to compare the effect of drip fertigation (the application of fertilizer through drip irrigation systems, DFI) on the leaching loss and transformation of urea-N in soil with that of surface fertilization combined with flood irrigation (SFI), and to study the leaching loss and transformation of three kinds of nitrogen fertilizers (nitrate fertilizer, ammonium fertilizer, and urea fertilizer) in two contrasting soils after the fertigation. In comparison to SFI, DFI decreased leaching loss of urea-N from the soil and increased the mineral N (NH₄⁺-N + NO₃^--N) in the soil. The N leached from a clay loam soil ranged from 5.7% to 9.6% of the total N added as fertilizer, whereas for a sandy loam soil they ranged between 16.2% and 30.4%. Leaching losses of mineral N were higher when nitrate fertilizer was used compared to urea or ammonium fertilizer. Compared to the control (without urea addition), on the first day when soils were fertigated with urea, there were increases in NH₄⁺-N in the soils. This confirmed the rapid hydrolysis of urea in soil during fertigation. NH₄⁺-N in soils reached a peak about 5 days after fertigation, and due to nitrification it began to decrease at day 10. After applying NH₄⁺-N fertilizer and urea and during the incubation period, the mineral nitrogen in the soil decreased. This may be related to the occurrence of NH₄⁺-N fixation or volatilization in the soil during the fertigation process.     

The behaviour of nitrogen fertilizers in neutral and acid loess soils II. Distribution and balances of 15 N-tagged nitrogen

A study, to investigate the remaining fertilizer-N in undisturbed soil columns from agricultural and forest soils after 60 days of percolation (see part I), was carried out. The columns were fertilized with two 15-N tagged nitrogen fertilizers (Ca(NO₃)₂ and (NH₄)₂SO₄) at a rate of 80kg N/ha. The investigation involved the distribution and fractionation of nitrogen in the soils. The soil columns were therefore cut into 8 segments and nitrogen forms analyzed were: total N, fixed-NH₄-N, exchangeable NH₄-N, NO₃-N and organic N. Consequently, the N-balances were established. It was ascertained that immobilization and gaseous losses from the fertilizers were higher after NH₄- than after NO₃-application in both soils. Immobilization in all treatments was temperature dependent and concentrated at the upper segments of the columns. The forest soil had higher incorporation than the agricultural soil. Nitrification was low in the forest soil while in the agricultural soil there was a fairly high nitrification even at 4°C. The balances showed losses of nitrogen in the range of 10 to 35 %. While this agrees with the findings of other workers in case of the agricultural soil, it leaves however, some questions unanswered in case of the forest soil.     

Nitrification in two coniferous forest soils after different fertilization treatments

The effects of seven different fertilization treatments on nitrification in the organic horizons of a Myrtillus-type (MT) and a Calluna-type pine forest in southern Finland were studied. No (NO^?₃ + NO^?₂)-N accumulated in unfertilized soils during 6 weeks at 14 or 20°C in the laboratory. Net nitrification was stimulated by urea in both soils (but more in the MT pine forest soil) and to a lesser degree by wood ash but not by ammonium nitrate or nitroform (ureaformaldehyde). Nitrification was not detected in nitroform fertilized soils although ammonium accumulation was high during incubation. In the MT pine forest soil, net nitrification appeared to be stimulated by apatite, biotite and micronutrients. Nitrapyrin inhibited nitrification indicating that it was carried out by autotrophic nitrifiers. In the urea-fertilized MT pine forest soil, nitrification took place at an incubation temperature of 0°C. Accumulation of (N0^?₃ + NO^?₂)-N was highest in soil sampled at < 10°C.     

Comparative Study on Disturbed and Undisturbed Soil Sample Incubation for Estimating Soil Nitrogen-Supplying Capacity

Application of nitrogen (N) fertilizers without knowing the N-supplying capacity of soils may lead to low N use efficiency, uneconomical crop production, and pollution of the environment. Based on the results from pot experiments treated with soil initial nitrate leaching and native soil, long-term alternate leaching aerobic incubation was conducted to study the disturbed and undisturbed soil N-supplying capacity of surface soil samples in 11 sites with different fertilities on the Loess Plateau. The results indicated that the entire indexes and ryegrass (Lolium perenne) uptake N with soil initial nitrate leaching showed a better correlation than that without soil initial nitrate leaching. Except the correlation coefficients for soil initial nitrate (NO₃ ^?)-N and mineral N extracted by calcium chloride (CaCl₂) before aerobic incubation with ryegrass uptake without soil initial nitrate leaching, the correlation coefficients for soil initial NO₃ ^?-N and mineral N extracted by CaCl₂ before aerobic incubation with ryegrass uptake with soil initial nitrate leaching and those for mineralizable N extracted by aerobic incubation, soil initial mineral N and mineralizable N extracted by aerobic incubation, potentially mineralizable N (N₀) and soil initial mineral N + N₀ with ryegrass uptake N under the two cases in disturbed treatment were all higher than those in undisturbed treatment. We concluded that NO₃ ^?-N in soil extracted by CaCl₂ before aerobic incubation can reflect soil N-supplying capacity but cannot reflect soil potential N-supplying capacity. Without soil initial nitrate leaching, the effect of disturbed and undisturbed soil samples incubated under laboratory conditions for estimating soil N-supplying capacity was not good; however, with soil initial nitrate leaching, this method could give better results for soil N-supplying capacity. Based on the results from pot experiments treated with soil initial nitrate leaching and native soil, the mineralization of disturbed soil samples can give provide better results for predicting soil N-supplying capacity for in situ structure soil conditions on the Loess Plateau than undisturbed soil samples.     

Nitrogen Saturation and Soil N Availability in a High-Elevation Spruce and Fir Forest

A field study was conducted during the summer of 1995 to gain abetter understanding of the causes of nitrate (NO₃-N)leaching and ongoing changes in soil nitrogen (N) availabilityin high-elevation (1524–2000 m) spruce (Picea rubens) andfir (Abies fraseri) forests of the Great Smoky MountainsNational Park, Tennessee and North Carolina, U.S.A. Indicatorsof soil N availability (total soil N concentrations,extractable NH₄-N, extractable NO₃-N, and C/N ratios)were measured in Oa and A horizons at 33 study plots. Dynamicmeasures included potential net soil N mineralization determinedin 12-week aerobic laboratory incubations at 22 °C.Potential net nitrification in the A horizon was correlated (r =+0.83, P < 0.001) with total soil N concentrations. Mostmeasures of soil N availability did not exhibit significanttrends with elevation, but there were topographic differences.Potential net soil N mineralization and net nitrification in theA horizon were higher in coves than on ridges. Relative amountsof particulate and organomineral soil organic matter influencedpotential net N mineralization and nitrification in the Ahorizon. Calculations indicate that soil N availability andNO₃-N leaching in high-elevation spruce and fir forests ofthe Great Smoky Mountains National Park will increase inresponse to regional warming.     

Leaching of nutrients from soil cores treated with a single large dose of digested sewage sludge

Core lysimeters containing undisturbed coarse sandy soil (from grassland) were amended with a high rate of anaerobically digested sewage sludge (equivalent to >1,000 t ha^–1). Water, at a rate equivalent to the mean weekly rainfall for the soil, was applied to amended and control lysimeters for 30 weeks and the leachate analysed for anions and cations. Lysimeters were also destructively sampled at intervals throughout the experiment and soil samples were analysed for extractable NH₄⁺-N, NO₃^–-N and PO₄^3–-P. Ammonium N leached for about 11 weeks from the amended lysimeters, then abruptly stopped. A similar amount of NO₃^–-N leached, but leaching was continuing when the experiment finished. The control lysimeters leached as much NO₃^–-N as those that were amended, but no NH₄⁺-N. The amended lysimeters also leached NO₂^–-N. Negligible PO₄^3–-P, but large amounts of SO₄^2– were leached from the amended lysimeters. Concentrations of extractable NH₄⁺-N and PO₄^3–-P were very high in the amended soils, but NO₃^–-N concentrations remained low throughout the experiment, indicating that nitrification rates were low and/or that denitrification rates were high.     

灌溉施肥对壤质潮土硝态氮淋溶的影响

在衡水市邓庄乡壤质潮上上进行了以灌水为主处理、氮用量为副处理,各五水平的定位试验。结果表明,氮肥用量是硝态氮淋溶损失的决定因素,冬小麦施氮150kghm-2不发生淋溶,施氮225～300kghm-2则硝态氮的淋溶增强。小麦播前基施氮肥量过高会使冬季发生硝态氮的淋溶。小麦拔节期和灌浆期灌溉一般不会引起硝态氮的淋溶损失;尽管一次灌水1350m3hm-2硝态氮的淋失量不高,但土壤剖面中的硝态氮含量显著比低灌水量的低。为降低硝态氮的损失,应控制一次灌水量不超过1050m3hm-2。雨季降水导致大量硝态氮淋溶损失,防治雨季土壤硝态氮的淋溶损失至关重要。     

DCD 在不同质地土壤上的硝化抑制效果和剂量效应研究

通过硝化抑制剂抑制土壤硝化作用是实现作物铵硝混合营养和提高氮肥利用率的重要途径之一。本试验采用室内模拟的方法, 在人工气候室(25 ℃)黑暗培养条件下, 应用新疆石灰性土壤研究了不同剂量的双氰胺(dicyandiamide, DCD)在砂土、壤土、黏土3 种不同质地土壤中对土壤硝态氮、铵态氮转化的影响及DCD 的剂量效应和硝化抑制效果。处理30 d 内, 各剂量DCD 处理对砂土的硝化抑制率为96.5%~99.4%(平均值为98.3%), 在黏土上为66.9%~85.6%(平均值为77.6%), 在壤土上为49.3%~79.4%(平均值为67.7%), 总体硝化抑制率表现为砂土>黏土>壤土。在砂土上DCD 的剂量效应不明显, DCD 用量从纯氮的1.0%增加到7.0%时, 土壤中硝态氮含量仅增加1.9~10.7 mg·kg^-1(培养30 d 时); 而在壤土和黏土中, 土壤硝态氮含量随DCD 浓度的增加而显著下降, 存在明显剂量效应。这说明施用DCD 可显著抑制新疆石灰性土壤的硝化作用过程, 在砂土、壤土、黏土中DCD 的最佳浓度分别为纯氮用量的6.0%、7.0%和7.0%, 并在培养30 d 内发挥显著作用。     

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。     

Characterization of nitrifying bacteria communities of soils from different ecological regions of China by molecular and conventional methods

Soil nitrification rate is very different among soil types, as a result of differences in physical and chemical properties. Little is known about the composition of the nitrifying bacteria community. In this investigation, three soils (fluvo-aquic soil, permeable paddy soil and red earth) from different geo-ecological regions in China were characterized for their nitrification activities and their nitrifying bacteria communities determined either by molecular approaches or by conventional culture methods. A 28-day long-term soil incubation showed that the maximum nitrification potential was found in the fluvo-aquic soil with almost 100% of inorganic N present as NO₃^–-N, while the minimum nitrification potential was in red earth with only a 4.9% conversion rate from ammonium into nitrate. There was no relationship between nitrification potential and numbers of nitrifiers in the soil. The conventional most probable number (MPN) method could enumerate ammonia oxidizers, but failed in enumerating nitrite oxidizers. Therefore, we used an MPN-PCR procedure which gave a convincing nitrite oxidizer count result, instead of MPN-diphylamine. Soils were characterized by denaturing gradient gel electrophoresis (DGGE) of DNA extracted from soils and amplified using a primer specific for the 16S rRNA gene and/or for the amoA gene. The DGGE columns of the three soils differed from each other. There were two similar bands present in DGGE columns of the fluvo-aquic and permeable paddy soils, but no similar band was found in DGGE columns of the red earth. The sequence of amoA indicated that all ammonia oxidizers in these soils were grouped into Nitrosospira clusters 1 and 3, and each soil had a common band similar to the other soils and a special band which differed from the other soils.     

Effect of Water Bicarbonate Concentration,pH and the Presence,or Not,of a Nitrification Inhibitor in the Nitrification Process

Ammonium (NH₄⁺) is an important nitrogen (N) source for plant growth. Nevertheless, NH₄⁺–N can be oxidized to nitrate (NO₃^?) by nitrification and then nitrate and nitrite can be leached into groundwater. The aims of this study were to investigate the effect of the water bicarbonate concentration, pH, and the presence, or not, of a nitrification inhibitor, on the nitrification process. Six treatments were established, changing the pH and the bicarbonate concentration, with or without the nitrification inhibitor. The results showed that an active nitrification process occurred in treatments with high pHs (8 and 7) and with no nitrification inhibitors. This causes an increase in the nitrate and nitrite concentration in the substrate. The use of N–NH₄⁺ fertilizers joint to a nitrification inhibitor, especially in nutritive solutions with a high concentration of bicarbonate and a pH of 8 and 7, decreases nitrate and nitrite accumulation in substrate which can prevent nitrate and nitrite leaching.     

Leaching of Nitrate,Ammonium, and Phosphate From Compost Amended Soil Columns

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).     

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.     

N-Source Effects on Temporal Distribution of NO3-N Leaching Losses to Subsurface Drainage Water

Understanding the temporal distribution of NO₃-N leaching losses from subsurface drained ‘tile’ fields as a function of climate and management practices can help develop strategies for its mitigation. A field study was conducted from 1999 through 2003 to investigate effects of the most vulnerable application of pig manure (fall application and chisel plow), safe application of pig manure (spring application and no-tillage) and common application of artificial nitrogen (UAN spring application and chisel plow) on NO₃-N leaching losses to subsurface drainage water beneath corn (Zea mays L.)–soybean (Glycine max L.) rotation systems as a randomized complete block design. The N application rates averaged over five years ranged from 166 kg-N ha^?1 for spring applied manure to 170 kg-N ha^?1 for UAN and 172 kg-N ha^?1 for fall applied manure. Tillage and nitrogen source effects on tile flow and NO₃-N leaching losses were not significant (P?<?0.05). Fall applied manure with CP resulted in significantly greater corn grain yield (10.8 vs 10.4 Mg ha^?1) compared with the spring manure-NT system. Corn plots with the spring applied manure-NT system gave relatively lower flow weighted NO₃-N concentration of 13.2 mg l^?1 in comparison to corn plots with fall manure-CP (21.6 mg l^?1) and UAN-CP systems (15.9 mg l^?1). Averaged across five years, about 60% of tile flow and NO₃-N leaching losses exited the fields during March through May. Growing season precipitation and cycles of wet and dry years primarily controlled NO₃-N leaching losses from tile drained fields. These results suggest that spring applied manure has potential to reduce NO₃-N concentrations in subsurface drainage water and also strategies need to be developed to reduce early spring NO₃-N leaching losses.