Fate Of Fertilizer Research Articles

Components of the fertiliser nitrogen balance for wheat production on duplex soils

In this paper, we review literature on the fate of fertiliser nitrogen (N) applied to duplex soils in wheat-growing regions of southern Australia, and discuss the contribution of specific N transformations to N loss. Duplex soils are characterised by the presence of soil material, within the rooting depth of crops, that possess hydraulic conductivities that are lower than those of overlying material. Denitrification and the transport of nitrate below rooting depth of crops are thought to be the chief causes of loss of fertiliser N and to contribute to poor grain yields. Ammonia volatilisation could contribute also to N loss. The fate of fertiliser N commonly applied to wheat in southern Australia has largely been evaluated using budgeting procedures using l5N, a stable isotope of N. Results from studies in south-eastem Australia, using red-brown earths, indicate that between 10 and 40% of applied 15N can be lost irrespective of time of application to wheat. Denitrification is believed to be the chief cause of loss of l5N. Similar studies on yellow duplex soils in Western Australia have shown fertiliser N loss to range from 70% to no loss of the l5N applied. The exact cause of N loss in Western Australian studies is unclear. There was circumstantial evidence for ammonia loss from surface-applied urea, and evidence of leaching of nitrates from this and other ammoniumbased fertilisers. The role of denitrification has not been clarified in Western Australian studies. In the majority of studies, recovery of 15N in aboveground biomass exceeded 40% of that applied. In addition, between 17 and 48% of applied 15N, of which 10-15% may be in root material, has been recovered in the soil organic matter pool. The predominance of the denitrification process in south-eastern Australian soils, and the inability to improve the efficiency of utilisation of 15N by delaying the time of application to wheat underscores the importance of controlling the nitrification process using inhibitors. Management options for Western Australian soils are less clear. Some agronomic experiments have demonstrated the advantage of delaying the application of fertiliser N to wheat to improve the efficiency of its utilisation. There is also evidence which suggests that N should be applied early in the growth cycle to promote tiller development and thereby increase the potential for grain yield.

Nitrogen fertilizer in leucaena alley cropping. I. Maize response to nitrogen fertilizer and fate of fertilizer-15N

Field microplot experiments were conducted in the semi-arid tropics of northern Australia to evaluate the response of maize (Zea mays L.) growth to addition of N fertilizer and plant residues and to examine the fate of fertilizer15N in a leucaena (Leucaena leucocephala) alley cropping system, in which supplemental irrigation was used. Leucaena prunings, maize residues and N fertilizer were applied to alley-cropped maize grown in microplots which were installed in the alleys formed by leucaena hedgerows spaced 4.5 metres apart. The15N-labelled fertilizer was used to examine the fate of fertilizer N applied in the presence of mulched leucaena prunings and maize residues.

Nitrogen Use by Tall Fescue and Switchgrass on Acidic Soils of Varying Water Holding Capacity

AbstractIncreased use of bunchgrasses on acidic soils of the humid Northeastern USA requires more detailed knowledge on the fate of fertilizer N for economic and environmental reasons. A 3‐yr field investigation using 15N‐depleted fertilizer was undertaken to determine the effect of soil water holding capacity (WHC) on the use of soil and fertilizer N by cool‐season (tall fescue, Festuca arundinacea Schreb.) and warm‐season (switchgrass, Panicum virgatum L.) forages. Three sites of varying soil depth provided WHC of 5, 15, and 25 cm. Fertilizer N was applied at 0, 90, and 180 kg ha−1 (split application for tall fescue). Three‐year production averages for Cut 1 switchgrass (mid‐July) were two‐ to three‐fold greater than for tall fescue (mid‐June) on all sites receiving N, and four‐fold greater on the two shallower sites without N. Cut 2 (late‐October) production was nearly equal for both species, with tall fescue averaging 50%, and switchgrass 10%, of Cut 1. Nitrogen concentration of both species generally increased with N rate but not with WHC. Total N uptake (TNU) increased with N rate for both cuts of tall fescue, but only for Cut 1 for switchgrass, on all sites. Percentage of TNU derived from fertilizer N ranged from 23 to 47% for tall fescue and 14 to 39% for switchgrass. Tall fescue and switchgrass recovered from 23 to 31% and 25 to 33%, respectively, of the fertilizer N applied to the two deeper sites. Only on the shallow Klinesville site at the 90 kg N level was there a significant difference in fertilizer‐ N recovery, where switchgrass recovered 31% compared to tall fescue at 19%. Although these results demonstrate relatively low recoveries by both species, the more efficient use of fertilizer N by switchgrass, both in terms of production and recovery, recommend its increased usage at low N rates in the Appalachian Region.

Corn Uptake and Soil Accumulation of Nitrogen: Management and Hybrid Effects

AbstractInefficient use of fertilizer N by corn (Zea mays L.) can result in the accumulation of excessive amounts of NO‐3 subject to leaching losses in the crop root zone. The fate of fertilizer N as influenced by N rate, nitrapyrin [2‐chloro‐6‐(trichloromethyl)pyridine], and corn hybrid was evaluated in a 3‐yr study with sprinkler‐irrigated corn. Variables were fertilizer‐N rate (75, 150, and 300 kg N/ha); nitrapyrin (0 and 0.5 kg/ha); and corn hybrid (Pioneer hybrids 3377, 3475, and 3551). Nitrogen was applied as late‐sidedressed (V6‐V9) NH3. The fate of fertilizer N was evaluated by measurement of apparent fertilizer‐N uptake (AFU), form of N in the fertilizer band prior to and following anthesis, and accumulation and distribution of N in the soil profile. There were no significant effects of hybrid on AFU across years, and no significant hybrid × nitrapyrin interactions on AFU. Nitrapyrin significantly reduced AFU across N rates and hybrids in 2 of 3 yr. Nitrate‐N concentrations in the fertilizer band, in the presence of nitrapyrin, were reduced prior to anthesis in 1986. Higher NH+4‐N concentrations in the fertilizer band in 1986, as well as trends towards higher total inorganic‐N concentrations all 3 yr following anthesis, suggest mineralization of temporarily immobilized fertilizer NH+4. Reduced AFU in the presence of nitrapyrin in 1986 and 1987 indicates reduced availability of fertilizer N consistent with a temporary immobilization process. Nitrate accumulation in the soil to a depth of 1.8 m after three growing seasons indicates a trend toward less NO‐3 accumulation where nitrapyrin was applied at N rates of 75 and 150 kg/ha. Nitrate concentrations in the soil at a depth of 1.8 m were significantly greater at the 150 and 300 kg N/ha rates, compared with the 75 kg N/ha rate or unfertilized soil, indicating probable movement of fertilizer N below the 1.8‐m depth at the higher rates. These results indicate that nitrapyrin should not be applied with NH3 at late‐sidedress time for this soil.

Selection of Nutrients to Enhance Biodegradation for the Remediation of Oil Spilled on Beaches1

ABSTRACT Laboratory studies were conducted to determine the fate of fertilizers proposed for application to the Alaska shoreline in support of the Alaskan Oil Spill EPA Bioremediation Project. Fertilizer application is thought to provide indigenous organisms with nutrients that appear to be limited on ocean beaches. The experiments were developed strictly to test the durability, release rates, and application procedures of a variety of fertilizer types. The effects of tidal movement on a beach were simulated by two separate conditions, static and dynamic. The static condition represented periods when the beach material was under water and turbulence was at a minimum. This condition was simulated in the laboratory by submerging the nutrient in a beaker of simulated seawater (with or without beach material, depending on the nutrients being tested). These experiments ran continuously over a three-month period, with water exchanges according to a planned schedule. Nutrient concentrations were measured in the exchanged water. Dynamic conditions represented the forces on beach material as the water moved from low to high tide and back to low tide. In the laboratory, the condition was simulated by applying the nutrients to beach material piled in one end of a long, narrow tray placed on a rocker table. When the rocker table was operating and enough seawater had been added to cover the beach material (in the rocker table's low position), a gentle sloshing of the water over the materials resulted. These experiments generally lasted one to two hours, during which time liquid samples were collected for nutrient analyses. Durability of the fertilizers was measured by visual observation and freeze/thaw determinations. The experimental setup was economical and performed well. The fertilizer most suited for field trial was found to be isobutyraldehyde diurea briquettes, which produced a slow, continuous release of nutrients.

FATE OF LABELLED FERTILIZER NITROGEN IN COMMERCIAL LOWBUSH BLUEBERRY STANDS

Labelled fertilizer nitrogen (15N) was applied to four commercial lowbush blueberry stands in order to assess the fate of fertilizer N. Thirteen weeks after application, 45 and 64% of the labelled fertilizer N was recovered from blueberry plants at Debert and Pigeon Hill, respectively. This suggests rapid uptake of fertilizer N by blueberry plants. Sixteen months after application, an average of 67% of the fertilizer N was recovered from the four sites. The results of this study support other evidence suggesting that lowbush blueberry systems conserve fertilizer N. Key words: Blueberry, 15N, fertilizer

Seasonal Changes in Smooth Bromegrass Top and Root Growth and Fate of Fertilizer Nitrogen

AbstractWhile information is available at the end of the growing season on the fate of fertilizer N applied to perennial grasslands, little detailed information is available on the transformations and translocation of N during a growing season. The purpose of this research was to measure the effect of N fertilization on time, quantities, and rates of dry‐matter accumulation by smooth bromegrass (Bromus inermis L.) tops and roots, water use, and fertilizer N transformations and uptake. Ammonium nitrate was surface broadcast at 0, 90, and 270 kg N ha−1 on established smooth bromegrass at Mandan, ND. At approximately 3‐wk intervals, top and root (0–900 mm) dry weights were measured, N uptake calculated, soil inorganic N concentrations determined, and apparent fertilizer N in tops, roots, and as soil inorganic N was calculated (fertilized minus check). Growth and N uptake of tops increased until physiological maturity in July, decreased during a midsummer drought, and increased after August rains. Fertilization greatly increased growth rate. For roots, growth stopped or even declined slightly at time of floral emergence in June, resumed until physiological maturity, remained constant or decreased slightly through the summer drought (when soil water reserves were depleted), then increased rapidly in September after fall rains. Dry matter accumulated at rates in excess of 300 kg ha−1 d−1 in May and September, when N uptake rates exceeded 4 kg ha−1 d−1. Over 40% of the fertilizer N at the 270 kg N rate was immobilized in organic forms other than root growth within 10 d after application, but by physiological maturity, 51% was in tops, 27% in roots, 3% as soil inorganic N, and only 19% was immobilized in other organic forms or lost by gaseous means (no leaching occurred). Results suggest that gaseous losses were no more than 10%. Nitrogen fertilization appeared to enhance three labile N pools—readily available (inorganic), highly labile (probably including microbial biomass), and moderately labile (possibly primarily grass roots).

The Effect of Growing Plants on Denitrification at High Soil Nitrate Concentrations

AbstractThe availability of plant rhizosphere C deposits and its influence on microbial denitrification is not clearly defined. Conflicting reports as to the influence of plants and root exudation on denitrification continue to appear in the literature. The results of our earlier phytotron study indicated that denitrification was not stimulated in soils planted with corn or wheat compared to unplanted soils. Lower nitrate concentrations in the planted soils, however, may have led to misinterpretation of this data. A second study was conducted, to evaluate the effect of actively growing plants on denitrification where the NO‐3 content of planted soils was maintained similar to unplanted soils. Simultaneously the C fixed by corn (Zea mays) and the fate of fertilizer N applied to the soil during the growing season were quantified. The corn was grown in a phytotron under a continuous supply of 14CO2 in 15N fertilized soils to which 15N‐NO‐3 was added periodically during the growing season. The results of these studies showed that denitrification was not stimulated in soils planted with corn during active plant growth phase even when soil NO‐3 was relatively high. Denitrification was, however, greater in corn planted than unplanted soil when the recoverable root biomass began to decrease. Less N was immobilized and net 15N immobilization was lower in planted soils than in unplanted soils. As denitrification was lower in planted soils during the time of active plant growth, the study suggests that root exudates did not stimulate either process.

Recovery of Fertilizer Nitrogen by Wheat as Affected by Fallow Method

AbstractThe fate of fertilizer N applied to crops is of both environmental and economic concern. To follow fertilizer N recovery in western Nebraska, depleted‐15N NH4NO3 was surface broadcast in April on winter wheat (Triticum aestivum L.) growing on plots fallowed the previous year by plowing, subtillage, and no‐till. Quantities of labeled N taken up by the growing crop, in the upper 100 mm of soil as inorganic N, and in both visible and partially decomposed crop residues, were followed on two sets of plots through the crop‐fallow‐crop sequence (approximately 117 weeks). About 16 to 18% of the labeled N was removed in the grain of the first wheat crop, with an additional 3 to 5% in the second crop. Labeled inorganic soil N decreased to <5% within 1 yr, with little effect of fallow method. No more than 4% was in visible residues at any time for all except no‐till fallow, for which 7 to 13% of the labeled N was found in visible residues from heading of the first crop through the entire fallow period until the second crop was seeded. Likewise, 4 to 9% of the labeled N applied was found in partially decomposed residues of no‐till during this period, compared to no more than 2% for the plow and subtill treatments. Total N in both residue pools combined decreased 50% from October to April of the fallow year for N‐fertilized wheat and 25% for unfertilized wheat. Most of the labeled N in the straw found in the visible residue pool by October was transferred over winter to either the partially decomposed pool or to other undetermined pools (including soil organic matter, microbial biomass, and losses to the atmosphere). Results show that, compared to plow and subtill, no‐till fallow enhanced retention of labeled N in the several crop residue pools and increased N uptake by the two wheat crops.

BIOLOGICAL IMMOBILIZATION OF FERTILIZER NITROGEN IN HUMID TROPICAL SOILS OF MAURITIUS

We studied the influence of the biological immobilization rate on the mobility and fate of fertilizer N under the humid climate of Mauritius in soil columns using (NH4)2SO4 labeled with 10% atom excess 15N and sorghum as the test plant. Our results showed that biological immobilization of fertilizer

Distribution of Applied Nitrogen in Soil—Pensacola Bahiagrass Components as Indicated by Nitrogen‐15

AbstractThe fate of fertilizer N applied to coarse‐textured soil‐plant systems is not well understood. To determine the effects of N rates and seasonal N applications on plant response and recovery of applied N from these soils, three field experiments with 15N‐enriched fertilizer were superimposed in 1976 on nontracer N experiments on Myakka fine sand (sandy, siliceous, hyperthermic Aeric Haplaquods), Ona fine sand (sandy, siliceous, hyperthermic Typic Haplaquods), and Astatula sand (hyperthermic, uncoated Typic Quartzipsamments) planted to Pensacola bahiagrass (Paspalum notatum Flugge). At each site, a split‐plot experimental design was used with two N rates (100 and 200 kg ha−1) as main plots and three seasonal N applications as subplots. Forages, stolon‐root masses, and soils were analyzed for total N and 15N concentrations. In 1976, forage yields and 15N‐labeled fertilizer N contents were larger at the higher N rate, but were not affected by seasonal N applications. Recovery of fertilizer N in forage was 36, 31, and 29% for the Myakka, Ona, and Astatula soils, respectively. An average of 48% of the total N in forage was from the fertilizer. Mineralization of immobilized N from previous fertilizations probably did not account for the large amount of nonfertilizer N in the forage. Recoveries of fertilizer N in stolon‐root masses were 11, 11, and 16%; recoveries in soils were 28, 13, and 11%; and recoveries in soil‐plant systems were 74, 54, and 54% from the Myakka, Ona, and Astatula soils, respectively. Denitrification was suspected as an important N loss mechanism from the poorly drained Myakka and Ona soils, and leaching was likely dominant from the well‐drained Astatula soil; however, soil‐solution samples collected from depths of 60 and 120 cm in these soils showed no evidence of N leaching. Not more than 5% of the 15N‐labeled fertilizer applied in 1976 was recovered in forage produced in 1977. At the end of 1977, total fertilizer N accounted for was essentially the same as at the end of 1976. Two important results were the relatively large amounts of nonfertilizer N in forage, especially in 1976, the year of 15N‐labeled fertilizer application, and the relatively high percentage of fertilizer N retained in these three sandy soils. In 1983, 7 yr after fertilization with labeled N, there was little change in labeled N in the soil compared to 1977.

Nitrogen‐15 Recovery for Five Years after Application of Ammonium Nitrate to Crested Wheatgrass

AbstractAlthough perennial grasses usually respond to N fertilization if there is adequate water, fertilizer N recovery is usually relatively low. This research was conducted to understand better the fate of fertilizer N applied to grasslands. Twenty open‐ended cylinders (102‐mm diam by 637‐mm length) were pressed into each of two main plots containing 4‐year‐old stands of crested wheatgrass [Agropyron desertorum (Fisch. ex Link) Schult.]. One plot had received no fertilizer N, and the other plot had received 22.4 g N/m2 each year since seeding. Enriched 15N was applied at the rate of 8.4 g N/m2 to a different replicated set of cylinders each of the 5 years of this study. Remaining cylinders received 8.4 g nonenriched N/m2 each year. Aboveground vegetation was harvested, and, after the fifth year, cylinders were removed from the soil. Roots were screened dry, and all plant material, roots, and soil were analyzed for total N and N‐isotope ratio.Average annual top growth varied fivefold as a result of highly variable precipitation and evaporation rate. Plant N concentration and uptake the first several seasons were about 25% greater from previously fertilized than from previously unfertilized soil. Cumulative recovery of 15N in tops increased with time, but considerable variation existed because of varied growing conditions between years. From 12 to 52% of the 15N applied was recovered in top growth in the season of application, representing about 75% of total isotope recovery in tops after four additional growing seasons. About 15% of the 15N was in roots after the first growing season, and about two‐thirds of this N appeared in plant tops within 3 y. Soil 15N varied from 29 to 49% of that applied, present mostly as organic N after the first season. About 70 to 95% of the 15N applied was accounted for in tops, roots, and soil, with little apparent relationship between 15N accounted for and either dry‐matter production or seasonal precipitation. Although uptake of soil N was initially 20 to 25% greater from previously fertilized than from unfertilized soil, this difference disappeared after the third year of fertilization, suggesting that at least 3 y of fertilization were required for the N cycle to readjust to a new steady state. Growing conditions the first few months after fertilizer application appear to have a major, but largely undefined, effect upon the fate of fertilizer N.

Experimental Site of the ‘Ecology of Arable Land’ Project

Abstract In 1979 a major integrated research project ‘The Ecology of Arable Land’ was initiated, in which recent trends in Swedish crop husbandry are reflected. These trends include less carbon input through crop residues, a higher nitrogen input through fertilizers, less biological fixation of nitrogen, through growing of legumes and simpler crop rotations. Nitrogen is the major limiting nutrient in modern agriculture. Crop uptake efficiency of nitrogen is low and pollution of waters and the atmosphere by nitrogen from fertilizer use is becoming increasingly evident. The project aims at quantitatively determining the fate of fertilizer and biologically-fixed nitrogen in four cropping systems (barely with 0 kg N ha−1 yr−1 barley with 120 kg N ha−1 yr−1, meadow fescue grass ley with 200 kg N ha−1 yr−1, lucerne ley with biological nitrogen fixation), with special attention to the role of soil organisms (microorganisms, fauna and roots) in regulating the biogeochemical nitrogen cycle. The experimental site o...

Evaluation of the acetylene‐inhibition technique for the measurement of denitrification in grassland soils

AbstractThe acetylene inhibition technique has been evaluated for its suitability for routine field measurements of denitrification in two soils under grass. Acetylene was introduced into the soil air by radial diffusion from probes inserted vertically into the soil and, using a soil cover, total denitrification was determined as the loss of nitrous oxide (N2O) from the acetylene‐treated soil. Acetylene concentrations of 0.1–1.0% (v/v), which are effective in inhibiting the reduction of N2O, were established within 1–2 h of commencing the supply of acetylene to soil at field capacity; the N2O flux equilibrated within the same period. Treatment and equilibration times were longer after rainfall on to a soil at field capacity and shorter in spring, summer and autumn when soil water content was less than field capacity. Spatial variability in N2O flux from acetylene‐treated soil was generally ±25% and was probably associated with variability in air‐filled pore spaces in the soil. Repeated treatments, as required in routine measurements of denitrification, did not affect the distribution of soil inorganic N between NH4+ and NO3‐ which suggests that concurrent inhibition of nitrification by acetylene was not a significant constraint in the field application of the technique. The efficiency with which acetylene inhibits the reduction of N2O was not affected by repeated treatments of soil nor was there any evidence for acetylene decomposition. Repeated treatments did not affect dry matter yield or mineral contents of herbage. The findings of this study suggest that the acetylene‐inhibition technique may be applied to routine measurements of denitrification in both small and large plot studies of the fate of fertilizer N.

Fertilizer Fate in a 13‐year‐old Slash Pine Plantation

AbstractSurface application of 403 kg N, 95 kg P, and 64 kg K per ha to a 13‐year‐old slash pine (Pinus elliottii Englem. var. elliottii) plantation on Caddo loam soil increased total volume growth during the next 6 years by 8.3 m3/(ha·year). Trees responded rapidly to the fertilizer; measurable differences in diameter growth developed by mid‐May. Fertilization markedly increased the amount of N, P, and K accumulated in current‐year needles during the first year after treatment. Fertilized trees continued to accumulate more P in current foliage for at least 8 years. Ratios of Rb/K in foliage indicated that K from the fertilizer comprised 27% of K accumulated in current‐year needles of fertilized trees during the fifth and sixth growing seasons, and 20% accumulated in the eigth. Ten months after treatment, added K had apparently disappeared from the top 13 cm of soil, but about half the added P remained available there. After 8 years, fertilized soil contained 40 ppm available P in the 0.9 cm layer; unfertilized soil contained only 2 ppm. In 8 years, fertilized plots accumulated 9.2 metric tons/ha more litter than did control plots. Litter had 50 kg/ha more N, 11.3 kg/ha more P, and 5.1 kg/ha more K than did litter on unfertilized plots. Disking to incorporate the fertilizer into the soil gave no advantage.

Residual Effects of N Fertilization on Dryland Spring Wheat in the Northern Plains. II. Fate of Fertilizer N1

AbstractResidual effects of fertilizer application on the fate of fertilizer N applied to crops in semiarid regions are largely unknown. Objectives of this study were to provide information on the recovery of fertilizer N during the fertilization and residual periods and to develop an N balance sheet for a continuous spring wheat (Triticum aestivum L.) cropping system.Ammonium nitrate was applied to spring wheat at 0 to 540 kg N/ha rate either (i) all in 1 year, (ii) one‐third in each of 3 years, or (iii) one‐sixth in each of 6 years to evaluate the availability and fate of fertilizer N in a dryland cropping system. Only grain was removed during harvest, and straw was plowed under each spring. Grain N uptake accounted for 31 to 46% of the total fertilizer N applied at 270 and 540 kg N/ha rate for various timing frequency. Fertilizer N uptake in straw and root biomass at the end of the experiment averaged 5 and 26 kg/ha, respectively. Movement of NO3‐N below the 90‐ cm depth (leaching) was detected for the 270 kg N/ha treatment, whether this total amount was applied all in 1 year, or 90 kg N/ha was applied in each for 3 years. However, with an annual application of 45 kg N/ha for 6 continuous years very little leaching of NO3‐N occurred. The amount of fertilizer N that moved beyond the root zone was greater at 540 than at 270 kg N/ha. Leaching of fertilizer N below 90 cm accounted for 4 to 37% of the total fertilizer applied, with greatest leaching occurring For the 1‐year treatment and least for the 6‐year treatment. Loss of N by runoff was negligible. The percent fertilizer N accounted for [(total fertilizer accountable ÷ total fertilizer applied) × 100] averaged 62, 64, and 66 for 1, 3, and 6‐year treatments, respectively. Unaccounted for fertilizer N possibly consisted of that portion of fertilizer N immobilized in soil organic fractions resistant to decomposition and that lost by volatilization. Results showed that if the N rate is adequate for maximum crop production, fertilizer efficiency is greatest when N is applied annually rather than at higher rates less frequently.

Fate of Fertilizer Nitrogen in a Flooded Rice Soil

AbstractIn order to improve the efficiency of fertilizer N utilization by rice (Oryza sativa L.), it is important to know what happens to N applied to the soil. Field experiments utilizing 15N‐enriched ammonium sulfate were carried out to determine the fate of fertilizer N (100 kg N/ha) applied to Crowley silt loam soil. The distribution of fertilizer N in the plant‐soil system at harvest time was determined using 2.32 m2 plots. The distribution of fertilizer N in the plant‐soil‐floodwater system at six times during the growing season was measured in smaller plots (0.28 m2).The results from the larger plots showed that fertilizer N recovered in the grain ranged from 30.9 to 37.3 kg N/ha depending on the method of application. Recovery of fertilizer N in the straw ranged from 18.2 to 24.2 kg N/ha. A considerable portion of fertilizer N (24.2 to 27.1 kg N/ha) remained in the soil (including roots) after cropping. Total recovery of the 100 kg/ha addition of labelled fertilizer N in the soil‐plant system was 75.0 to 85.6 kg N/ha for the different methods of N application examined. Experiments using the smaller 0.28 m2 plots showed rapid uptake of fertilizer N immediately after application, with no apparent further uptake after about 3 weeks. Soil N was the major and perhaps sole source of N for the plant during the last part of the growing season.

Nitrogen Conservation under Corn Planted in Quackgrass Sod

AbstractThe mechanics of growing corn (Zea mays L.) in a grass sod using the no‐tillage concept have recently been developed. However, little is known abouthe fate of fertilizers, especially nitrogen, or the potential uses of such plant species as quackgrass (Agropyron repens L.) in this management system. Silage yields of corn were determined from field studies in which corn sod‐planted in quackgrass, treated with six rates of atrazine, was compared to conventionally planted corn. The effects of no tillage and conventional tillage, using two rates of atrazine on total soil N, and N mineralization potential were compared. Yields of corn silage produced in herbicide‐treated quackgrass were significantly higher than yields from conventional tillage. In the first year, silage yields increased with rates of atrazine. Quackgrass persisted for a 2‐year period at the three lowest rates of atrazine but not at higher rates. After the first season, mineral N (largely NO3‐N) was significantly greater under untilled quackgrass than under plowed plots, However, by the following spring differences associated with tillage method had disappeared. Soil N mineralization potential, NO, and total N in the 0‐ to 15‐cm layer were considerably higher for untilled than for plowed soils. However, in untilled plots, these values were unaffected by rate of atrazine.

Recovery, Residual Effects, and Fate of Nitrogen Fertilizer Sources in a Semiarid Region1

AbstractInformation on recovery and eventual fate of fertilizer N applied to dryland crops in the northern Great Plains is needed to optimize economic returns and to minimize pollution hazards. In a field experiment at Mandan, N. Dak., four fertilizer N sources were applied to separate areas of corn (Zea mays L.) and bromegrass (Bromus inermis L.) for 4 years. From the fifth through seventh years, the two areas were uniformly seeded to barley (Hordeum vulgare L.) without additional N fertilization, until residual effects were no longer significant. Sources of N used were ammonium sulfate, ammonium nitrate, calcium nitrate, and urea, applied at either 55 or 110 kg/ha to Parshall fine sandy loam. Recovery of fertilizer N in corn plant tops was greatest for ammonium nitrate. Over 35% of the calcium nitrate and urea applied at 110 kg/ha of N to corn was leached below the root zone. Leaching of fertilizer N applied to bromegrass was insignificant. Except for urea, fertilizer N recovery by bromegrass from the other N sources was nearly equal and usually higher at 55 kg/ha. Residual growth responses were smaller from N applied to bromegrass than to corn. About 70 to 95% of the fertilizer N applied was accounted for by the end of the residual period, except for lower values for several of the urea treatments. Gaseous losses were probably high for urea surface broadcast on bromegrass at 110 kg/ha of N because only 47% could be accounted for and no residual effects were observed.

Water Quality in Relation to Farm Use of Fertilizer

In spite of the enormous increase in the use of commercial fertilizers containing N and P in the last 30 years, there is little direct evidence that they contribute generally to significant water quality deterioration. However, there are areas of overuse or unusual circumstances where nitrate in significant concentration may reach underground water. Phosphate use on farms appears to present no pollution problems provided soil erosion is controlled. Much is unknown about the fate of fertilizer N not recovered by crops. Separation of the effects of fertilizers from other sources of nutrients arising from industry, sewage, and soil degradation incident to cultivation is difficult. Fertilizer restriction would produce serious reductions in yield of most crops, particularly vegetables and fruit. More land would be needed for crop production and the erosion hazards increased. Legal restriction on use of fertilizers should be considered only on a watershed basis, and not on a state or national basis.