Accumulation Of Nitrate Nitrogen Research Articles

Research progress on collocation planting of crops for decreasing the loss of soil nitrate nitrogen through leaching

农业生产中为获得较高作物产量而投入大量的化学肥料, 同时不合理的田间管理措施使硝态氮在土壤中大量累积, 增加了淋溶风险。不同作物搭配生长及种植模式在协同提高作物产量、充分利用光热资源、提高集约化生产能力方面是一种有效的栽培措施, 同时在高效利用土壤养分、改善生态环境、降低硝态氮污染方面具有很大潜力。本文从不同类型作物搭配生长及不同种植模式(设施蔬菜与填闲作物、粮食作物与经济作物、粮食作物与粮食作物、粮食作物与露地蔬菜、蔬菜与蔬菜)方面综述了高效利用土壤氮素、降低土壤硝态氮累积与淋失的效果, 并根据不同类型作物特点进行了机理上的解释。文末以搭配作物根系为突破点对作物种植模式进行了研究展望。

Effect of hydraulic retention time on performance of an anoxic–aerobic sequencing batch reactor treating saline wastewater

The effects of hydraulic retention time on the performance and microbial community structure of an anoxic–aerobic sequencing batch reactor treating saline wastewater were investigated. The average removal efficiencies of chemical oxygen demand and ammonia nitrogen decreased from 90 and 85 % to 68 and 71 % with the decrease in hydraulic retention time from 17 to 9 h, respectively. No obvious accumulation of nitrate nitrogen and nitrite nitrogen in the effluent was found. The contents of polysaccharide and protein in extracellular polymeric substances increased with the decrease in hydraulic retention time. The polysaccharide/protein ratio decreased from 1.18 to 1.11 with the decrease in hydraulic retention time from 17 to 9 h. The increase in extracellular polymeric substances with the decrease in hydraulic retention time led to the increase in sludge volume index. The specific ammonium oxidation rate, specific nitrite oxidation rate, specific nitrate reduction rate, and specific oxygen uptake rate increased with the decrease in hydraulic retention time. The diversity indices of microbial community decreased from 2.69 to 2.39 with the decrease in hydraulic retention time from 17 to 9 h. The α-proteobacteria were the dominant groups under hydraulic retention time of 17, 14, 11, and 9 h, which constituted 46, 30, 40, and 40 % of the whole microbial community, respectively.

Effects of nitrogen rate on nitrate-nitrogen accumulation in forage kale and rape crops

Nitrogen fertilizer is applied to supplement soil nitrogen supply to maximize forage brassica crop dry-matter production. However, nitrogen fertilizer applications in excess of that required to maximize growth result in potentially toxic nitrate–nitrogen (NO3–N) concentrations in grazeable plant tissues. Three experiments, two for forage kale at Lincoln (Canterbury) and one for forage rape at Hastings (Hawke's Bay) in New Zealand were grown under different rates of nitrogen (0–500 kg N ha−1) to determine the effect of different rates of nitrogen on NO3–N content of different plant parts of the crops. One of the kale experiments was grown with either full irrigation or no rain and no irrigation over summer, hereafter referred to as summer drought. The NO3–N concentration on a whole plant (weighted average) basis increased from 0·1 mg g−1 dry matter for the control plots to 2·30 mg g−1 for the 500 kg N ha−1 plots for forage kale. It increased from 0·99 for the control plots to 3·37 mg g−1 for the 200 kg N ha−1 plots for forage rape crops. However, NO3–N concentration increased with N supply under the summer-drought plots from an average of 0·33 mg g−1 when ≤120 kg N ha−1 was applied to 2·30 mg g−1 for the 240 kg N ha−1 treatments but was unaffected by N supply under irrigation. The NO3–N concentrations were higher in the stems and the petiole (which included the midrib of the leaf) than leaves in all three experiments. The NO3–N concentration was highest at the bottom of the kale stem and decreased towards the top. We recommend N application rates based on soil tests results, and for conditions similar to the current studies up to 300 kg N ha−1 under irrigation and adjusted lower N rates for regions prone to dry summers.

Nitrate accumulation in forage brassicas

Previous research has shown that the application of fertilizer nitrogen (N) can lead to an accumulation of nitrate nitrogen (NO3-N) in forage brassicas, particularly when N application rates exceed that required to obtain maximum crop yield. However, there are no data examining the effect of timing of fertilizer application on NO3-N accumulation. An experiment was established in 2009 with four forage brassica crops (turnips, rape, kale and swedes) and three N fertilizer treatments (early N, late N and double N) at Lincoln, Canterbury, New Zealand. The N treatments, which differed among crops depending on crop duration, consisted of rates and timings of N fertilizer. For the turnips and rape, the early N treatment consisted of 200 kg N/ha applied 16 days after sowing; the late N treatment consisted of 200 kg N/ha applied 40 days after sowing; and the double N treatment consisted of 200 kg N/ha applied 16 days after sowing and a further 200 kg N/ha applied 40 days after sowing. For the kale and swedes, the early N treatment consisted of 400 kg N/ha applied 16 days after sowing; the late N treatment consisted of 400 kg N/ha applied 72 days after sowing; and the double N treatment consisted of 400 kg N/ha applied 16 days after sowing and a further 400 kg N/ha applied 72 days after sowing. There were differences in yield between species that reflected their growth duration but no yield differences between N treatments. Averaged across all species, plant NO3-N content was greater in crops that received the double rate of N than either the early or late N treatments. Importantly, the late N treatment (3.7 mg/g) accumulated almost double (P < 0.001) the plant NO3-N content of the early N treatment (2.0 mg/g). Averaged across all N treatments, the leafy crops (rape and kale) (5.5 mg/g) had nearly double (P < 0.001) the NO3-N content of the bulb crops (turnip and swedes) (2.9 mg/g). In general, the stems had the highest NO3-N content across all crops, followed by the bulbs. Leaves had the lowest NO3-N content. Overall, these results indicate that early application of fertilizer N could be used to minimize NO3-N accumulation in forage brassicas.

Alternate furrow irrigation and nitrogen level effects on migration of water and nitrate-nitrogen in soil and root growth of cucumber in solar-greenhouse

Water and nitrogen in soil have a great effect on growth and productivity of cucumber (Cucumis sativus L.), which is widely cultivated with high economic benefit in solar greenhouse in North China. To understand the effects of alternate furrow irrigation (AFI) and nitrogen levels on migration of water and nitrogen in soil, accumulation of nitrate-nitrogen (NO3−-N) and root growth of cucumber in the solar greenhouse, cucumber variety Jinyu No. 5 was fertilized with different amounts of nitrogen [no nitrogen (CK2), optimal nitrogen (AINo), conventional nitrogen (AINc)] under AFI. Conventional furrow irrigation and conventional nitrogen were used as the control (CK1). The results indicated that soil NO3−-N content, electrical conductivity values in the 0–20cm, 20–40cm and 40–60cm layers, and soil residual NO3−-N content at the end of the two growing seasons were all increased as the nitrogen fertilizer increased under AFI, especially in the top layer of soil (0–20cm). However, compared with conventional furrow irrigation, AFI with optimized fertilizer led to increases of root length, root biomass yield, root–shoot ratio of the cucumber crop and economic coefficient (K). AFI also greatly improved both biomass and economic yield water use efficiency. Altogether, AFI with optimized fertilizer (AINo) was a good irrigation practice in the solar greenhouse for increasing the use efficiency of both water and fertilizer, reducing salinity accumulation in the top soil, and maintaining economic yield of cucumber crop.

Trace elements present in airborne particulate matter—Stressors of plant metabolism

Changes of amino acid concentrations (glutamic acid, glutamine, asparagine, aspartate, proline, tryptophan, alanine, glycine, valine and serine), gas-exchange parameters (net photosynthetic rate, transpiration rate, stomatal conductance and intercellular CO2 concentration) and nitrate levels in Lactuca serriola L. under airborne particulate matter (PM) contamination reported here reveal their role in plant chronic stress adaptation. Results of the pot experiment confirmed the toxic effect of trace elements present in PM for lettuce. PM applied to soil or on the lettuce leaves were associated with the strong inhibition of above-ground biomass and with the enhancement of plant trace element contents. The significant changes of amino acid levels and leaf gas-exchange parameters of the plants showed strong linear dependences on PM contamination (R2=0.60–0.99). PM application on leaves intensified toxic effect of trace elements (As, Pb, Cr and Cd) originating from PM by shading of the leaf surface. The plant accumulation of nitrate nitrogen after PM contamination confirmed to block nitrate assimilation.

The effects of ozone and water exchange rates on water quality and rainbow trout Oncorhynchus mykiss performance in replicated water recirculating systems

Rainbow trout Oncorhynchus mykiss performance and water quality were evaluated and compared within six replicated 9.5m3 water recirculating aquaculture systems (WRAS) operated with and without ozone at various water exchange rates. Three separate studies were conducted: (1) low water exchange (0.26% of the total recycle flow) with and without ozone; (2) low water exchange with ozone versus high water exchange (2.6% of the total recycle flow) without ozone; and (3) near-zero water exchange (only backwash replacement) with and without ozone. Mean feed loading rates for WRAS operated at high, low, and near-zero exchange were 0.40, 3.98, and 55.9kgfeed/m3 makeup water, respectively. Ozone significantly reduced total suspended solids, color, and biochemical oxygen demand and resulted in a significant increase in ultraviolet transmittance (%) (P<0.10). Ozone also created ambient water quality within low exchange WRAS that was comparable to that of WRAS operated at high water exchange (P>0.10). Additionally, dissolved copper and iron were significantly lower within WRAS operated with ozone (P<0.10). Dissolved zinc was also consistently lower in WRAS operated with ozone, but not significantly (P>0.10). In Studies 1 and 3, total ammonia nitrogen and nitrite nitrogen were slightly lower within the ozonated systems, but were not always significantly lower. In all studies, ozone did not prevent nitrate nitrogen accumulation. At the conclusion of Study 1, rainbow trout growth was significantly greater within low exchange WRAS operated with ozone (P=0.001). At the conclusion of Study 2, rainbow trout growth was similar between treatments (P=0.581), indicating that fish grew equally as well within ozonated WRAS operated at 1/10th the flushing rate as the non-ozonated and high flushing control systems. Overall, ozone created an improved water quality environment within low and near-zero exchange WRAS that generally resulted in enhanced rainbow trout growth rates, survival, feed conversion, and condition factor.

Short-Term Irrigation Level Effects on Residual Nitrate in Soil Profile and N Balance from Long-Term Manure and Fertilizer Applications in the Arid Areas of Northwest China

A field experiment was conducted to determine the effects of long-term applications of fertilizers and manure (1982 to 2003) and short-term irrigation level (2002 and 2003) on accumulation of nitrate nitrogen (NO3-N) in soil at Zhangye Oasis, China. The treatments included manure (M) and no manure (M0) as main plots; check (Ck), nitrogen (N), nitrogen + phosphorus (NP), and nitrogen + phosphorus + potassium (NPK) as subplots; and two amounts of irrigation (I1 and I2) as subsubplots. The application of N alone resulted in large NO3-N accumulation in soil, accounting for 6% of the applied N, and the lowest crop N recovery. Application of manure resulted in increased NO3-N in the soil profile compared to treatment with no manure, and the MN treatment resulted in the greatest amount of NO3-N in soil. Nitrogen applied with P and/or K reduced the amount of NO3-N in soil in both manure and no-manure treatments compared with N only. The unaccounted N was greatest (60%) in the N-alone treatment and lowest (30%) in the NPK treatment. When manure plus fertilizer were applied together, the unaccounted N ranged from 35%–42%. Based on results from only 2 years, greater amounts of irrigation (I2) caused greater leaching of NO3-N in the soil profile compared with I1, especially in treatments receiving manure. The implications of these findings are that these high amounts of accumulated NO3-N in surface and subsoil layers can be a potential threat to surface water, underground water, and air quality in the long run. This accumulated N in the soil profile can be used as a source of available N for future crops and should be recycled by using proper crop, soil, fertilizer, and water-management strategies/practices. The findings also suggest the need for further research to make an effective and efficient use of this accumulated NO3-N in the soil profile in order to save cost of N fertilizer application to future crops.

Effects of long-term fertilization modes on spatio-temporal distribution and accumulation of soil nitrate nitrogen in solar greenhouse

通过连续7 年的定位试验, 研究了日光温室生产中不同施肥模式(常规模式、无公害模式和有机模式)对土壤NO₃^--N 时空分布及累积的影响。结果表明, 随着种植年限的增加, 3 种施肥模式土壤剖面各层次NO₃^--N含量均呈上升趋势, 年增加量顺序为常规施肥模式＞无公害施肥模式＞有机施肥模式。受氮素输入量(施肥)的影响, NO₃^--N 主要分布在0~40 cm 土层, 0~60 cm 土层NO₃^--N 含量总体呈作物生长前期低、中期高、后期低的趋势; 与上层土壤相比, 100 cm 以下土层NO₃^--N 含量有不同程度的增加。0～200 cm 土体NO₃^--N 平均累积量有机施肥模式比无公害施肥模式低33.8%, 比常规施肥模式低45.9%; 无公害施肥模式比常规施肥模式低18.3%。3 种施肥模式下, NO₃^--N 都有向2 m 以下土体淋洗的趋势。与施用化学肥料相比, 施用有机肥能明显降低土壤剖面NO₃^--N 含量, 控制其累积峰的下移, 但不合理施用有机肥也会产生NO₃^--N 淋洗而污染环境。

Combinations of Horizontal and Vertical Flow Constructed Wetlands to Improve Nitrogen Removal

Nitrogen removal in wetlands is achieved through two pathways: (a) N cycling and (b) storage. N cycling is a permanent removal pathway. There has been an increasing interest in the development of technologies to alleviate permanent nitrogen removal limitation in constructed wetlands by ensuring prevalence of conditions enhancing N cycling. The purpose of this study is to review an emerging technology of vegetated submerged bed constructed wetland system aimed at improving nitrogen removal in wetlands through rational system design. The design and performance of this system type is evaluated. The oxygen transfer capacity and nitrogen removal mechanisms on system performance are evaluated. Constructed wetland combinations most commonly consist of vertical flow (VF) and horizontal flow (HF) beds where VF and HF are aimed at nitrification and denitrification, respectively. Nitrate nitrogen accumulation is the most limiting factor in typical VF based systems.

Fluctuations of nitrogen levels in soil profile under conditions of a long-term fertilization experiment

The present study is focused on the correlation between varied long-term fertilization and changes in soil nitrogen concentrations. It was found that all fertilization systems significantly increased the levels of total, mineral and organic nitrogen in the soil profile. Organic fertilizers (manure and slurry) contributed to a more considerable increase in the concentrations of total nitrogen and nitrogen undergoing hydrolysis in 6M HCl, compared to mineral fertilizers. Ammonia nitrogen dominated over nitrate nitrogen among mineral nitrogen forms. Organic fertilization contributed to nitrate nitrogen accumulation, while mineral fertilization to ammonia nitrogen storage. The highest accumulations of nitrate nitrogen and ammonia nitrogen were observed after the application of slurry and manure, respectively. Hydrolyzable nitrogen content and its proportion in total nitrogen generally decreased with soil depth. An increase in the levels of organic nitrogen forms, i.e. nitrogen contained in amino sugars and amino acids as well as ammonia nitrogen from decomposition of amides, amino sugars and amino acids, was conditioned primarily on the application of organic fertilizers, particularly manure. Amino acid-N dominated among hydrolyzable nitrogen compounds (77%), while amino sugar-N accounted for 5.6% only.

Crop yield, nitrogen uptake and nitrate-nitrogen accumulation in soil as affected by 23 annual applications of fertilizer and manure in the rainfed region of Northwestern China

Application of chemical fertilizers and farmyard manure affects crop productivity and improves nutrient cycling within soil–plant systems, but the magnitude varies with soil-climatic conditions. A long-term (1982–2004) field experiment was conducted to investigate the effects of nitrogen (N), phosphorus (P), and potassium (K) fertilizers and farmyard swine manure (M) on seed and straw yield, protein concentration, and N uptake in the seed and straw of 19-year winter wheat (Triticum aestivum L.) and four-year oilseed (three-year canola, Brassica napus L. in 1987, 2000 and 2003; one-year flax, Linum usitatisimum L. in 1991), accumulation of nitrate-N (NO3-N) in the soil profile (0–210 cm), and N balance sheet on a Huangmian soil (calcaric cambisols, FAO) near Tianshui, Gansu, China. The two main plot treatments were without and with farmyard swine manure (M); sub-plot treatments were control (Ck), N, NP, and NPK.␣The average seed yield decreased in the order MNPK ≥ MNP > MN ≥ NPK ≥ NP > M > N > Ck. The average effect of manure and fertilizers on seed yield was in the order M > N > P > K. The seed yield increase was 20.5% for M, 17.8% for N, 14.2% for P, and 2.9 % for K treatment. Seed yield response to fertilizers was much greater for N and P than for K, and it was much greater for no manure than for manure treatment. The response of straw yield to fertilization treatments was usually similar to that of seed yield. The N fertilizer and manure significantly increased protein concentration and N uptake plant. From the standpoint of increasing crop yield and seed quality, MNPK was the best fertilization strategy. Annual applications of N fertilizer and manure for 23 successive years had a marked effect on NO3-N accumulation in the 0–210 cm soil profile. Accumulation of NO3-N in the deeper soil layers with application of N fertilizer and manure is regarded as a potential danger, because of pollution of the soil environment and of groundwater. Application of N fertilizer in combination with P and/or K fertilizers reduced residual soil NO3-N significantly compared with N fertilizer alone in both no manure and manure plots. The findings suggest that integrated and balanced application of N, P, and K fertilizers and␣manure at proper rates is important for protecting soil and groundwater from potential NO3-N pollution and for maintaining high crop productivity in the rainfed region of Northwestern China.

Impact of harvesting and logging slash on nitrogen and carbon dynamics in soils from upland spruce forests in northeastern Ontario

The potential impact of timber harvesting in the boreal forest on aquatic ecosystem water quality and productivity depends in part on the production of nutrients within the soil of the harvested catchment. Nitrogen supplied by organic matter decomposition is of particular interest because of the important role that N plays in biotic processes in surface waters, and in forest nutrition in general. Logging slash quality and input to the forest floor has the potential to influence N availability after harvest on clearcut sites. Net production of organic and inorganic-N and microbial biomass C and N concentrations were determined during a 90-day laboratory incubation at constant temperature and moisture. Incubated soils included F horizon and shallow mineral soil horizons (0–5 cm) from unharvested and full-tree harvested (2 and 12 growing seasons since harvest) boreal forest sites at the Esker Lakes Research Area (ELRA), in northeastern Ontario, Canada. In an ancillary experiment, black spruce foliage was added to unharvested forest floor material after 30 days during a 90-day laboratory incubation to simulate the influence of logging slash from full-tree harvesting on C and N dynamics. Twelve-year old clearcut F horizon material released on average 75 and 5 times more NO 3 - -N and 3 and 2 times as much inorganic-N than soil collected from unharvested and 2-year-old clearcuts, respectively. This increase in NO 3 - -N accumulation during the incubation was accompanied by decreases in both exchangeable NH 4 + -N and microbial biomass C and N levels. Net daily changes in microbial biomass N were significantly related to organic and inorganic-N accumulation or loss within the F horizon. Mineral soil release of inorganic-N was lower than release from the forest floor. Nitrate-nitrogen accumulation was lower, and NH 4 + -N accumulation was higher in mineral soil from unharvested sites when compared to 12-year-old clearcuts. Calculated harvest response ratios indicated that incubated mineral soil from the 12-year-old clearcut sites released significantly greater amounts of NO 3 - -N than 2-year-old clearcuts. Incorporation of black spruce needles into F horizon material reduced the production of organic and inorganic-N and increased microbial biomass N. Laboratory incubations of F horizon and shallow mineral soil from 12-year-old clearcuts suggested that these boreal soils have the capacity for increased inorganic-N production compared to uncut stands several years after harvesting. This has the potential to increase N availability to growing boreal forest plantations and increase N leaching due to greater NO 3 - -N levels in the forest soil.

Impact of Land Use Practices on Faunal Abundance, Nutrient Dynamics and Biochemical Properties of Desert Pedoecosystem

Increased dependence of resource-poor rural communities on soils of low inherent fertility are the major problem of desert agroecosystem. Agrisilviculture practices may help to conserve the soil biota for maintaining essential soil properties and processes in harsh climate. Therefore, the impacts of different land use systems on faunal density, nutrient dynamics and biochemical properties of soil were studied in agrisilviculture system of Indian desert. The selected fields had trees (Zizyphus mauritiana, Prosopis cineraria, Acacia nilotica) and crops (Cuminum cyminum, Brassica nigra, Triticum aestivum) in different combinations. Populations of Acari, Myriapoda, Coleoptera, Collembola, other soil arthropods and total soil fauna showed significant changes with respect to different land use practices and tree species, indicating a strong relation between above and below ground biodiversity. The Coleoptera exhibited greatest association with all agrisilviculture fields. The Z. mauritiana system indicated highest facilitative effects (RTE value) on all groups of soil fauna. Soil temperature, moisture, organic carbon, nitrate- and ammonical-nitrogen, available phosphorus, soil respiration and dehydrogenase activity were greater under tree than that of tree plus cropping system. It showed accumulation of nitrate-nitrogen in tree field and more utilization by crops in cultivated lands. Positive and significant correlation among organic carbon, nitrate- and ammonical-nitrogen, phosphorus, soil respiration and dehydrogenase activity clearly reflects increase in soil nutrients with the increase in microbial and other biotic activity. P. cineraria field was the best pedoecosystem, while C. cyminum was the best winter crop for cultivation in desert agroforestry system for soil biological health and soil sustainability. The increase in organic carbon, soil nutrients and microbial activity is associated with the increase in soil faunal population which reflect role of soil fauna in fertility building. This suggests that strategies may be developed for nurturing fertility-building soil fauna and managing degraded pedoecosystem in desert just by adopting suitable agricultural practices.

Long‐Term Fertilization Effects on Crop Yield and Nitrate Nitrogen Accumulation in Soil in Northwestern China

A long‐term (1982 to 2000) field experiment was conducted at Zhangye, Gansu, China, on a sandy clay loam (Typic Anthrosol) under wheat (Triticum aestivum L.)–wheat–corn (Zea mays L.) rotation to determine the effects of N, P, and K chemical fertilizers and farmyard manure (M) on grain and straw yield, harvest index (HI), protein concentration, and N uptake in grain and straw and accumulation of nitrate N (NO3–N) in the soil profile (0–180 cm). The eight treatments from various combinations of fertilizers and M were check, N, NP, NPK, M, MN, MNP, and MNPK. Mean grain yield decreased in the order of MNPK ≥ MNP &gt; NPK &gt; MN &gt; NP &gt; M &gt; N &gt; check (i.e., 8.01, 8.00, 7.51, 7.28, 7.00, 5.50, 4.89, and 3.43 Mg ha−1, respectively). Yield response to applied N and P increased with time since yields in the check plots declined with time. Potassium fertilizer application provided no, slight, and dramatic increase in grain yield during the initial 6 yr, next 5 yr, and last 8 yr, respectively. Response of straw yield to fertilizers and M was similar to the grain yield. Mean HI increased with fertilizers in no‐M treatments for both crops. Crude protein concentration and N uptake in grain and straw increased markedly with fertilizers, and M increased it further. Fertilizers (N, NP, and NPK) led to NO3–N accumulation in most subsoil layers. Combined applications of fertilizers and M reduced soil NO3–N accumulation in soil compared with fertilizers alone. In conclusion, the findings suggest that it is important to use balanced application of chemical fertilizers and M at proper rates in order to protect soil and underground water from potential NO3–N pollution while also sustaining high crop production.

Recycling soil nitrate nitrogen by amending agricultural lands with oily food waste.

With current agricultural practices the amounts of fertilizer N applied are frequently more than the amounts removed by the crop. Excessive N application may result in short-term accumulation of nitrate nitrogen (NO3-N) in soil, which can easily be leached from the root zone and into the ground water. A management practice suggested for conserving accumulated NO3-N is the application of oily food waste (FOG; fat + oil + greases) to agricultural soils. A two-year field study (1995-1996 and 1996-1997) was conducted at Elora Research Center (43 degrees 38' N, 80 degrees W; 346 m above mean sea level), University of Guelph, Ontario, Canada to determine the effect of FOG application in fall and spring on soil NO3-N contents and apparent N immobilization-mineralization of soil N in the 0- to 60-cm soil layer. The experiment was planned under a randomized complete block design with four replications. An unamended control and a reference treatment [winter wheat (Triticum aestivum L.) cover crop] were included in the experiment to compare the effects of fall and spring treatment of oily food waste on soil NO3-N contents and apparent N immobilization-mineralization. Oily food waste application at 10 Mg ha(-1) in the fall decreased soil NO3-N by immobilization and conserved 47 to 56 kg NO3-N ha(-1), which would otherwise be subject to leaching. Nitrogen immobilized due to FOG application in the fall was subsequently remineralized by the time of fertilizer N sidedress, whereas no net mineralization was observed in spring-amended plots at the same time.

The effects of tillage systems and crop rotations on soil chemical properties of a Black Chernozemic soil

The effects of zero (ZT), minimum (MT) and conventional tillage (CT) systems and three 4-yr crop rotations on soil total C and N, mineralizable N, NO3-N, P, K and SO4-S accumulation and distribution in the soil profile were determined after one 4-yr cycle of crop production on Black Chernozemic Indian Head heavy clay soil. The distributions of available P and K in the profile were not affected by tillage or rotation. Total C and N in the 0–5 cm depth was higher in the reduced tillage systems than in CT, but differences in the 5–10 cm and 10–15 cm depths were not significant. Nitrate concentration was higher in the 15–30 cm and 30–60 cm depths under CT than under reduced tillage. Inclusion of fallow increased accumulation of NO3-N in the deeper soil depths, while inclusion of winter wheat in the rotation reduced deep movement of NO3-N. Nitrate-nitrogen accumulation after field pea production was comparable to that after winter wheat, but a greater proportion of the NO3-N was present near the soil surface after winter wheat, reducing the potential for leaching below the rooting zone. Potential for movement of NO3-N below the rooting zone may be increased by fallow and decreased by production of winter wheat and by reduced tillage systems. Key words: Tillage, rotations, nitrate, sulphate

Factors Affecting the Stabilization Period of Sewage Sludge in Soil with Reference to the Gel Chromatographic Pattern

Effects of the sludge loading rate, soil properties, dewatering agent in sludge, and incubation temperature on the stabiIization period of dewatered sewage sludge in soil were investigated with reference to the gel chromatographic patterns of the water extracts from the soil-sludge mixtures. The stabiIization period was defined as the period until which a specific pattern of the gel chromatogram appears, indicating both the presence of small amounts of free ammonia and the accumulation of nitrate nitrogen in soil. A high sludge loading rate above 5% resulted in a longer stabilization period, especially in the Fujimi loamy coarse sand soil. The stabiIization period was shorter in the Hiratsuka coarse sandy loam soil than in the other two kinds of soils (Fujimi loamy coarse sand soil and Sekiya fine sandy loam soil). Lime, used as a dewatering agent, shortened the stabiIization period at low sludge loading rates, but prolonged it at high sludge loading rates, compared with a polymeric organic coagulant. Temperature was the most significant factor to affect the stabilization period. As the temperature decreased from 25 to 5°C, the period of stabilization increased drastically. The stabiIization process of sewage sludge in soil was interpreted as a process of nitrogen transformation consisting of ammonification and nitrification. The limiting step in the stabiIization process was the nitrification step. The period was prolonged whenever nitrification was inhibited, while ammonification was little inhibited except at a low temperature.

Nitrate-Nitrogen Accumulation In Furrow Irrigated Fields and Effects of Sugarbeet Production

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Influence of growing various crops in five different fixed rotations on the changes in nitrate and total nitrogen content of soils

SummaryThe results on the influence of various crops in five different fixed rotations on the ohanges in nitrate and total N content of soils are reported. Groundnut contributed largely to the accumulation of nitrate nitrogen in the soil profile (to a depth of 120 cm). Bajra fodder exhausted the soil nitrogen reserve to a great extent. Wheat and maize, in a rotation, reduced nitrate leaching to deeper soil layers. Summer moong also left a large amount of unabsorbed nitrate in the profile. Total nitrogen content of the soil decreased after the harvest of cereals. Maximum depletion occurred after the harvest of bajra crop. Potato (a crop which received a heavy dressing of N fertilizer) and legumes contributed to the soil N reserve. A balance sheet of N indicated net gains of total soil N in four of the five cropping sequences. A net loss of 75 kg N/ha was observed in bajra fodder-potato-wheat rotation.