Relationships between microbial biomass nitrogen,nitrate leaching and nitrogen uptake by corn in a compost and chemical fertilizer-amended regosol

Abstract

To determine the relationships between microbial biomass nitrogen (N), nitrate–nitrogen leaching (NO₃-N leaching) and N uptake by plants, a field experiment and a soil column experiment were conducted. In the field experiment, microbial biomass N, 0.5 mol L^?1 K₂SO₄ extractable N (extractable N), NO₃-N leaching and N uptake by corn were monitored in sawdust compost (SDC: 20 Mg ha^?1 containing 158 kg N ha^?1 of total N [approximately 50% is easily decomposable organic N]), chemical fertilizer (CF) and no fertilizer (NF) treatments from May 2000 to September 2002. In the soil column experiment, microbial biomass N, extractable N and NO₃-N leaching were monitored in soil treated with SDC (20 Mg ha^?1) + rice straw (RS) at five different application rates (0, 2.5, 5, 7.5 and 10 Mg ha^?1 containing 0, 15, 29, 44 and 59 kg N ha^?1) and in soil treated with CF in 2001. Nitrogen was applied as (NH₄)₂SO₄ at rates of 220 kg N ha^?1 for SDC and SDC + RS treatments and at a rate of 300 kg N ha^?1 for the CF treatment in both experiments. In the field experiment, microbial biomass N in the SDC treatment increased to 147 kg N ha^?1 at 7 days after treatment (DAT) and was maintained at 60–70 kg N ha^?1 after 30 days. Conversely, microbial biomass N in the CF treatment did not increase significantly. Extractable N in the surface soil increased immediately after treatment, but was found at lower levels in the SDC treatment compared to the CF treatment until 7 DAT. A small amount of NO₃-N leaching was observed until 21 DAT and increased markedly from 27 to 42 DAT in the SDC and CF treatments. Cumulative NO₃-N leaching in the CF treatment was 146 kg N ha^?1, which was equal to half of the applied N, but only 53 kg N ha^?1 in the SDC treatment. In contrast, there was no significant difference between N uptake by corn in the SDC and CF treatments. In the soil column experiment, microbial biomass N in the SDC + RS treatment at 7 DAT increased with increased RS application. Conversely, extractable N at 7 DAT and cumulative NO₃-N leaching until 42 DAT decreased with increased RS application. In both experiments, microbial biomass N was negatively correlated with extractable N at 7 DAT and cumulative NO₃-N leaching until 42 DAT, and extractable N was positively correlated with cumulative NO₃-N leaching. We concluded that microbial biomass N formation in the surface soil decreased extractable N and, consequently, contributed to decreasing NO₃-N leaching without impacting negatively on N uptake by plants.     

Soil-Applied Nitrogen and Composted Manure Effects on Soybean Hay Quality and Grain Yield

ABSTRACT

Grain yield in many soybean experiments fails to respond to fertilizer nitrogen (N). A few positive responses have been reported when soybean were grown in the southern U.S., when N was applied near flowering and when biosolids were added. In a previous study, low N concentrations of soybean forage in north Texas on a high pH calcareous soil were reported and thus, we suspected a N nutrition problem. Consequently, we initiated this study to determine whether selected preplant N sources broadcast and incorporated into a Houston Black clay (fine, smectitic, thermic Udic Haplusterts) might increase forage N concentration, forage yield, or soybean grain yield. In 2003, N was applied as ammonium nitrate (NH₄NO₃, AN) up to 112 kg N ha^{? 1} and dairy manure compost (DMC) was applied at rates of 4.9, 9.9, 15.0, and 19.9 Mg ha^{? 1}. The DMC contained 5.9, 2.6, and 6.7 g kg^{? 1} of total N, P, and K, respectively; thus DMC added 29 to 116 kg N ha^{? 1}. In 2004, AN was applied at rates of 112 and 224 kg N ha^{? 1} and DMC was applied at 28 and 57 Mg ha^{? 1}; thus, DMC added 168 to 335 kg N ha^{? 1}. In another 2004 test, biosolids, a biosolids/municipal yard waste compost mixture (BYWC), and AN were compared. The biosolids contained 31, 18, and 2.9 g kg^{? 1} total N, P, and K, respectively. The BYWC mixture contained 8.8, 6.1, and 3.4 g kg^{? 1} of total N, P, and K, respectively. Biosolids were applied at 10 Mg ha^{? 1} (310 kg N ha^{? 1}), BYWC was applied at 58 Mg ha^{? 1} (510 kg N ha^{? 1}), and AN up to 224 kg N ha^{? 1}. None of the soil treatments increased soybean grain yield or forage yield although AN slightly increased forage N concentration in 2003.     

Are Indicators for Critical Load Exceedance Related to Forest Condition?

The aim of this study was to evaluate the suitability of the (Ca?+?Mg?+?K)/Al and the Ca/Al ratios in soil solution as chemical criteria for forest condition in critical load calculations for forest ecosystems. The tree species Norway spruce, Sitka spruce and beech were studied in an area with high deposition of sea salt and nitrogen in the south-western part of Jutland, Denmark. Throughfall and soil water were collected monthly and analysed for pH, NO₃-N, NH₄-N, K, Ca, Mg, DOC and Al_tot. Organic Al was estimated using DOC concentrations. Increment and defoliation were determined annually, and foliar element concentrations were determined every other year. The throughfall deposition was highest in the Sitka spruce stand (maximum of 40 kg N ha^?1yr^?1) and lowest in the beech stand (maximum of 11 kg N ha^?1yr^?1). The Sitka spruce stand leached on average 12 kg N ha^?1yr^?1 during the period 1988–1997 and leaching increased throughout the period. Only small amounts of N were leached from the Norway spruce stand whereas almost no N was leached from the beech stand. For all tree species, both (Ca?+?Mg?+?K)/Al and Ca/Al ratios decreased in soil solution at 90 cm depth between 1989 and 1999, which was mainly caused by a decrease in concentrations of base cations. The toxic inorganic Al species were by far the most abundant Al species at 90 cm depth. At the end of the measurement period, the (Ca?+?Mg?+?K)/Al ratio was approximately 1 for all species while the Ca/Al ratio was approximately 0.2. The lack of a trend in the increment rates, a decrease in defoliation as well as sufficient levels of Mg and Ca in foliage suggested an unchanged or even slightly improved health condition, despite the decreasing and very low (Ca?+?Mg?+?K)/Al and Ca/Al ratios. The suitability of these soil solution element ratios is questioned as the chemical criteria for soil acidification under field conditions in areas with elevated deposition rates of sea salts, in particular Mg.     

Nitrate leaching,nitrous oxide emission and N use efficiency of aerobic rice under different N application strategy

A field study was conducted in the sub-humid tropical region of India to examine the effect of different nitrogen (N) management strategies on nitrate leaching, nitrous oxide (N₂O) emission and N use efficiency in aerobic rice. Treatments were: control (no N), 120 kg N ha^?1 applied as prilled urea (PU) in conventional method, 120 kg N ha^?1 applied as neem coated urea (NCU) in conventional method, N applied as PU on the basis of leaf colour chart (LCC) reading, N applied as NCU on the basis of LCC reading, and 120 kg N ha^?1 applied as PU and farm yard manure (FYM) in 1:1 ratio. Results showed that 3.4–16.1 kg NO₃-N ha^?1 was leached below 45 cm depth and 0.61–1.12 kg N₂O-N ha^?1 was emitted from aerobic rice during the growing season. NCU when applied conventionally reduced nitrate-nitrogen (NO₃-N) leaching and N₂O emission by 18.6% and 21.4%, respectively However when applied on the basis of LCC reading NCU reduced NO₃-N leaching by 39.8% as compared to PU applied in conventional method. NCU when applied on the basis of LCC reading synchronized N supply with demand and reduced N loss, which resulted in higher yield and N use efficiency.     

Reducing Nitrogen Leaching from Agriculture: An Essential Step toward Protecting the Environment in High Rainfall Areas of Taiwan

ABSTRACT

Reducing nitrogen (N) leaching from croplands is important to protect environmental quality and improve recovery of applied N. To contribute to this broader goal of nutrient management, a simple pot experiment evaluated the potential differences among urea (250 kg N ha^?1), urea+compost (125 kg N ha^?1 from urea + 125 kg N from 8 Mg ha^?1 of compost), compost (250 kg N from 16 Mg ha^?1 of compost) and a zero control (Ctrl), in terms of their effects on apparent N recovery (ANR), mineral N (N_min) leaching and soil retention of applied N. Cabbage (Brassica oleraceae L.) and corn (Zea mays L.) were grown in rotation where compost application was not repeated in the 2nd year. N_min leaching was monitored by adding 83 mm and 62 mm of water fortnightly to cabbage and corn crops, respectively for a total of 28 times in a two-year period. Combined (urea+compost) and independent (compost) treatment application retained 1.5 to 2 times higher N, and lowered 2.1 to 4.6 times N_min leaching, relative to independent (urea) application. We conclude that farmers’ practice of fertilization that has an inherent problem of N leaching for high rainfall areas in Taiwan could be improved by proper compost and urea combinations within agronomically recommended rates of N application.     

Nitrogen Availability from Compost in High Tunnel Tomato Production

High yield agricultural systems, such as high tunnel (HT) vegetable production, require a large supply of soil nutrients, especially nitrogen (N). Compost is a common amendment used by HT growers both to supply nutrients and to improve physical and biological soil properties. We examined commercially-available composts and their effects on soil N, plant N uptake, and tomato yield in HT cultivation. In addition, a laboratory study examined N and carbon (C) mineralization from the composts, and the usefulness of compost properties as predictors of compost N mineralization was assessed under field and laboratory conditions. The field study used a randomized complete block design with four replications to compare four compost treatments (all added at the rate of 300 kg total N ha^?1) with unamended soil and an inorganic N treatment (110 kg N ha^?1). Tomatoes were grown in Monmouth, Maine during the summers of 2013 and 2014. Compost NO₃^?-N and NH₄⁺-N application rates were significantly correlated with soil NO₃^?-N and NH₄⁺-N concentrations throughout the growing season. Marketable yield was positively correlated with compost total inorganic N and NO₃^?-N in both years, and with NH₄⁺-N in 2014. There were no significant differences among composts in percentage of organic N mineralized and no correlations were observed with any measured compost property. In the laboratory study, all compost-amended soils had relatively high rates of CO₂ release for the initial few days and then the rates declined. The compost-amended soils mineralized 4%–6% of the compost organic N. This study suggested compost inorganic N content controls N availability to plants in the first year after compost application.     

Nitrate leaching loss under annual and perennial pastures with and without lime on a duplex (texture contrast) soil in humid southeastern Australia

Mineral N accumulates in autumn under pastures in southeastern Australia and is at risk of leaching as nitrate during winter. Nitrate leaching loss and soil mineral N concentrations were measured under pastures grazed by sheep on a duplex (texture contrast) soil in southern New South Wales from 1994 to 1996. Legume (Trifolium subterraneum)‐based pastures contained either annual grass (Lolium rigidum) or perennial grasses (Phalaris aquatica and Dactylis glomerata), and had a control (soil pH 4.1 in 0.01 m CaCl₂) or lime treatment (pH 5.5). One of the four replicates was monitored for surface runoff and subsurface flow (the top of the B horizon), and solution NO₃^– concentrations. The soil contained more mineral N in autumn (64–133 kg N ha^?1 to 120 cm) than in spring (51–96 kg N ha^?1), with NO₃^– comprising 70–77%. No NO₃^– leached in 1994 (475 mm rainfall). In 1995 (697 mm rainfall) and 1996 (666 mm rainfall), the solution at 20 cm depth and subsurface flow contained 20–50 mg N l^?1 as NO₃^– initially but < 1 mg N l^?1 by spring. Nitrate‐N concentrations at 120 cm ranged between 2 and 22 mg N l^?1 during winter. Losses of NO₃^– were small in surface runoff (0–2 kg N ha^?1 year^?1). In 1995, 9–19 kg N ha^?1 was lost in subsurface flow. Deep drainage losses were 3–12 kg N ha^?1 in 1995 and 4–10 kg N ha^?1 in 1996, with the most loss occurring under limed annual pasture. Averaged over 3 years, N losses were 9 and 15 kg N ha^?1 year^?1 under control and limed annual pastures, respectively, and 6 and 8 kg N ha^?1 year^?1 under control and limed perennial pastures. Nitrate losses in the wet year of 1995 were 22, 33, 13 and 19 kg N ha^?1 under the four respective pastures. The increased loss of N caused by liming was of a similar amount to the decreased N loss by maintaining perennial pasture as distinct from an annual pasture.     

Nitrate leaching in an organic dairy/crop rotationas affected by organic manure type, livestock densityand crop

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 1^st 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 2^nd 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 1^st 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.     

Comparing Nitrate-N Losses through Leaching by Field Measurements and Nitrogen Balance Estimations

Nitrogen (N) balance method is a valuable tool for estimating N losses. However, this technique could lead to incorrect estimates of the amount of nitrate (NO₃^?N) leaching if processes relevant to N losses are not considered properly. The aim of this study was to compare NO₃^?-N leaching losses estimated using an N balance (nonrecovered N, Nne) with data of NO₃^?-N leaching losses (Nl). The experiment was made on a Typic Argiudoll soil planted with corn (five growing seasons) under 0, 100, and 200 kg N ha^?1. The ceramic soil-water suction samplers were installed (1 m deep). Drainage was estimated by the LEACH-W model. The greatest overestimation with the N balance method occurred for years with annual rainfall below the historical average and at times of high NO₃^?-N availability. Future research should focus on investigating mechanisms of N losses relevant under limited water availability.     

Mineralization and N Fertilizer Equivalent Value of Composts as Assessed by Tall Fescue (Festuca arundinacea)

The capability to determine nitrogen availability of composts is necessary to ensure that such materials will provide sufficient fertilization to the growing crop and cause minimal environmental degradation. A greenhouse study using tall fescue as a bioindicator was used to evaluate nitrogen availability of two biosolids composts, two mixed yard waste-poultry manure composts, and one commercially-processed poultry litter. Five inorganic nitrogen (as NH₄NO₃-N) treatments applied at 0, 22.5, 45, 67.7, and 90 mg N/kg soil were employed to establish an N calibration curve. Yield, fescue biomass total nitrogen (as total Kjeldahl N (TKN)), and soil TKN and KCl extractable NO₃^?-N and NH₄⁺-N concentrations of the organically amended treatments were compared to the inorganically fertilized treatments to determine amendment N mineralization rates and N fertilizer equivalent values (NFEV). Nitrogen mineralization rates were greatest in the poultry litter (21%) and Panorama yard waste compost (5%) amended pots. The NFEV of these amendments were 49% and 10%, respectively. Wolf Creek biosolids compost and Huck's Hen Blend yard waste compost immobilized N (?5% and 0.18%, respectively), and had percent NFEV of ?0.66% and 0.19%, respectively. Rivanna biosolids compost immobilized N (?15%), but the NFEV was 30% due to the relatively high inorganic N content in the amendment. Nitrogen mineralization and NFEV were generally greater in amendments with greater total N concentrations and lower C:N values. The total N concentration and C:N values were less reliable variables in predicting N mineralization and percent NFEV when a significant portion of the total N was in the inorganic form. Nitrogen equivalency value and N mineralization for each amendment increased with time of sampling, indicating the potential for early season N insufficiency to plants fertilized with compost due to lack of synchrony between N mineralization and plant N needs.     

NITRATE ACCUMULATION IN SPINACH AS INFLUENCED BY SULFUR AND PHOSPHORUS APPLICATION UNDER INCREASING NITROGEN LEVELS

Nitrate (NO₃) accumulation by spinach was studied under increasing nitrogen (N) levels (60, 120 and 240 kg N ha^?1) along with sulfur (45 kg S ha^?1) and phosphorus (P; 90 kg P₂O₅ ha^?1) application. Plants were harvested at 50 and 65 days after sowing. Plant samples were analyzed for NO₃-N and total N, P, S, potassium (K), calcium (Ca), and magnesium (Mg). Radio assay of 35S was done to estimate percent sulfur derived from fertilizer and percent fertilizer sulfur utilization. Spinach maintained a very high level of NO₃-N in its tissue throughout the growing period. NO₃-N was increased with increasing nitrogen level and was reduced with phosphorus and sulfur application and also with advancement in growth. Total N, P, S, K, Ca and Mg uptake were increased with increasing nitrogen levels as well as with application of sulfur and phosphorus. Sulfur application caused increase in percent sulfur derived from fertilizer and percent utilization of fertilizer sulfur.     

A lysimeter study of nitrate leaching from grazed grassland as affected by a nitrification inhibitor,dicyandiamide, and relationships with ammonia oxidizing bacteria and archaea

Nitrate (NO₃^?) can contribute to surface water eutrophication and is deemed harmful to human health if present at high concentrations in the drinking water. In grazed grassland, most of the NO₃^?‐N leaching occurs from animal urine‐N returns. The objective of this study was to determine the effectiveness of a nitrification inhibitor, dicyandiamide (DCD), in decreasing NO₃^? leaching in three different soils from different regions of New Zealand under two different rainfall conditions (1260 mm and 2145 mm p.a.), and explore the relationships between NO₃^?‐N leaching loss and ammonia oxidizing bacteria (AOB) and ammonia oxidizing archaea (AOA). The DCD nitrification inhibitor was found to be highly effective in decreasing NO₃^?‐N leaching losses from all three soils under both rainfall conditions. Total NO₃^?‐N leaching losses from the urine patch areas were decreased from 67.7–457.0 kg NO₃^?‐N/ha to 29.7–257.4 kg NO₃^?‐N/ha by the DCD treatment, giving an average decrease of 59%. The total NO₃^?‐N leaching losses were not significantly affected by the two different rainfall treatments. The total NO₃^?‐N leaching loss was significantly related to the amoA gene copy numbers of the AOB DNA and to nitrification rate in the soil but not to that of the AOA. These results suggest that the DCD nitrification inhibitor is highly effective in decreasing NO₃^? leaching under these different soil and rainfall conditions and that the amount of NO₃^?‐N leached is mainly related to the growth of the AOB population in the nitrogen rich urine patch soils of grazed grassland.     

Growth of Rhododendron,Rudbeckia and Thujia and the Leaching of Nitrates as Affected by the pH of Potting Media Amended with Biosolids Compost

A conventional potting media containing peat moss, softwood bark and sand was amended to contain 0,25,50,75 and 100 (percent vol^?1) municipal compost made from yard waste and biosolids. Each medium was adjusted with limestone and sulfur to an approximate pH of 5.0, 6.0 or 7.0. Rhododendron Panticum L. ‘Anah Kruschke’ (Rhododendron), Thujia occidentalis L. (Arborvitae) and Rudbeckia hirta L. ‘Goldilocks’ (Black-eyed Susan) were grown in each medium and pH level for 18 months. Leachate from pots was tested for NO₃-N and NH₃-N+NH₄-N to determine how media pH and the amount of compost effected the potential for potting media to be a source of nitrate in surface and ground water.

Media pH affected plant growth more than the percent compost. Compared to media with a pH of 7.0, statistically significant increases in the growth of Rhododendron occurred in media with a pH of 5.0 or 6.0. This pH effect was similar but less pronounced for Thujia. Growth of Rudbeckia was not effected by media pH or percent compost. Media with 0 and 25 percent compost leached the least nitrogen regardless of pH. Media with 75 and 100 percent compost at pH 5.0 and 6.0 leached the most nitrogen. The increase in nitrogen leaching in the more acidic media was associated with higher concentrations NH₃-N+NH₄-N. Nitrogen in leachate was greatest during the four weeks immediately after the pots were placed in the field and four weeks after fertilizer was applied in June of the second year of the experiment.     

稻田土壤中氮素淋失的研究

本文应用稻田大型原状土柱渗漏计，研究了双季稻田土壤中氮素随渗漏水流淋失的形态、数量、季节性变化以及若干农化因子的影响。明确了稻田中氮素淋失的基本形态是硝态氮（ＮＯ３＾－－Ｎ），估算出双季稻田中氮素淋失总量可接近３０ｋｇＮ／ｈａ，同时肯定了农田施用氮肥对地下水体环境可能的ＮＯ３＾－－Ｎ污染，建议双季稻田中每季水稻的氮肥用量宜控制在１５０ｋｇＮ／ｈａ；本文还证实氮肥用量对氮素淋失有明显影响，不同氮肥品     

北京地区潮土表层中NO3--N的转化积累及其淋洗损失

本试验利用渗滤池设施，采用化学分析和同位素技术相结合的方法研究了北京地区潮土表层中施用氮肥后ＮＯ３＾－－Ｎ转化积累及其１３０ｃｍ土体的淋洗状况。常规分析结果表明，在春小麦和夏玉米的生育前期可以观察到氮素明显地向ＮＯ３＾－－Ｎ的转化积累，其强度随尿素施用量的增加而明显增加，而尿素、硝铵、硫铵等不同氮肥品种处理之间有差异但大多不显著。同时夏玉米期间转化积累作用比春小麦期间强烈。＾１５Ｎ标记试验结果表明     

Leaching of mineral nitrogen in the soil influenced by addition of compost and N-mineral fertilizer

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 N_min 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 N_min was detected in the variant C2 where 140 kg N ha^?1 was applied, in both vegetation periods (5.97 kg N_min ha^?1 after the first vegetation period and 17.02 kg N_min 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 N_min ha^?1 and 5.79 kg N_min 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 N_min leaching.     

Long-term nitrogen balance for pearl millet (Pennisetum glaucum L.) in an acid sandy soil of Niger

On acid sandy soils of Niger (West Africa) fertilizer N recovery by pearl millet (Pennisetum glaucum L.) is often more than 100 per cent in years with normal or above average rainfall. Biological nitrogen fixation (BNF) by N₂-fixing bacteria may contribute to the N supply in pearl millet cropping systems. For a long-term field experiment comprising treatments with and without mineral fertilizer (F) and with and without crop residue application (CR) a N balance sheet was calculated over a period of six years (1983-1988). After six years of successive millet cropping total N uptake (36-77 kg N ha^?1 yr^?1) was distinctly higher than the amount of fertilizer N applied (30 kg N ha^?1 yr^?1). The atmospheric input of NH₄-N and NO₃-N in the rainwater was about 2 kg N ha_?1 yr^?1, 70 % in the form of NH₄-N. Gaseous NH₃ losses from urea (broadcast, incorporated) were estimated from other experiments to amount to 36 % of the fertilizer N applied. Nitrogen losses by leaching (15 to > 25 kg N ha^?1 yr^?1) were dependent on the treatment and on the quantity and distribution of single rainfall events (>50 mm). Decline in total soil N content (0-60 cm) ranged from 15 to 48 kg N ha^?1 yr^?1. The long-term N balance (1983-1988) indicated an annual net gain between 6 (+CR-F) and 13 (+CR+F) kg N ha^?1 yr^?1. For the control (-CR-F) the long-term N balance was negative (10 kg N ha^?1 yr^?1). In the treatment with crop residues only, the N balance was mainly determined by leaching losses, whereas in treatments with mineral fertilizer application the N balance depended primarily on N removal by the millet crop. The annual net gain in the N balance increased from 7 kg ha^?1 with mineral fertilizer to 13 kg ha^?1 in the combination mineral fertilizer plus crop residues. In both the rhizosphere and the bulk soil (0-15 cm), between 9 and 45% of the total bacterial population were N₂-fixing (diazotrophic) bacteria. The increased N gain upon crop residue application was positively correlated with an increase in the number of diazotrophic and total bacteria. The data on bacterial numbers suggest that the gain of N in the longterm N balance is most likely due to an N input by biological nitrogen fixation. In addition, evidence exists from related studies that the proliferation of diazotrophs and total bacteria in the rhizosphere due to crop residue application stimulated root growth of pearl millet, and thus improved the phosphorus (P) acquisition in the P deficient soil.     

Low soil C:N ratio results in accumulation and leaching of nitrite and nitrate in agricultural soils under heavy rainfall

Nitrate (NO^-₃) and nitrite (NO₂^-) leaching threatens groundwater quality.Soil C:N ratio,i.e.,the ratio of soil organic carbon to total nitrogen,affects mineralization,nitrification,and denitrification;however,its mechanism for driving soil NO^-₃ and NO^-₂ accumulation and leaching remains unclear.Here,a field investigation in a fluvo-aquic soil and a soil column experiment were performed to explore the relation...     

Impact of Organic Amendments on Groundwater Nitrogen Concentrations for Sandy and Calcareous Soils

Experiments were conducted on calcareous and sandy soils to investigate the effects of organic amendments for vegetable production on groundwater nitrogen (N) concentration in south Florida. The treatments consisted of applying yard and food residuals compost, biosolids compost, a cocompost of the municipal solid waste and biosolids, and inorganic fertilizer. Nitrate nitrogen (NO₃-N), ammonium nitrogen (NH₄-N), and total N concentrations were collected for a period of two years for both soils. Statistical analysis results revealed that for the three species tested, there were no significant differences among treatments. NO₃-N concentrations for all treatments remained less than the maximum contamination level (10 mg/L). NO₃-N transport to groundwater was higher in calcareous soil (mean=5.3 mg/L) than in sandy soil (mean=0.6 mg/L). NH₄-N concentrations ranged from 0 to 13.6 mg/L throughout the experiment. Calcareous soil had lower NH₄-N concentrations (mean=0.1 mg/L) than sandy soils (mean=0.7 mg/L). Total N ranged from 0.4 to 21.7 mg/L for all treatments for both soils reflecting high adsorption of dissolved organic N in both soils. Overall, results indicated that all the compost treatments were comparable to inorganic fertilizer with regard to N leaching and N concentrations in the groundwater while producing similar or higher yields.     

Evaluation of Compost for Use as a Soil Amendment in Corn and Soybean Production

The purpose of this research project was to 1) evaluate rate of compost application and 2) to compare compost with uncomposted raw material and inorganic fertilizer N application upon maize and soybean growth and productivity, and upon soil characteristics. During the first three years of the study, the source of uncomposted material and compost was food waste and ground newsprint. During years 4 to 9 of the study, the source of uncomposted material and compost was dairy cow manure and wood chips. Application rates in field site 1 were 0, 11.2, 22.4, 33.6 and 44.8 Mg ha^?1 compost, 44.8 Mg ha^?1 uncomposted material and 140 kg ha^?1 fertilizer N (as urea). Application rates in field site 2 were 0, 22.4, 44.8, 67.2 and 134.4 Mg ha^?1 compost, 134.4 Mg ha^?1 uncomposted manure and 180 kg ha^?1 fertilizer N (dry matter basis). The high rates of compost application significantly raised organic matter levels, and available P and K compared to inorganic fertilizer N. Uncomposted manure and increasing compost application rates significantly increased grain yield, number of kernels per plant and plant weight. Composting significantly reduced pathogen indicator bacteria concentrations. The data of this study suggest that on these high organic matter soils 22.4 Mg ha^?1 to 44.8 Mg ha^?1 are optimal compost application rates.