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Fertilizer N applied in the fall or early spring is often used less efficiently than N applied closer to the time of maximum N demand by plants. Nitrification inhibitors make it possible to delay nitrification of applied NH4+‐N in the soil and thereby reduce overwinter and early spring N loss from leaching and denitrification. Because NH4+absorption may induce changes in plant mineral composition, we evaluated under field conditions, the effect of inhibiting nitrification of NH4+‐N on the mineral composition of corn leaf tissue as well as on grain yield and protein content. Anhydrous ammonia with and without nitrapyrin [ 2‐chloro‐6‐(trichloromethyl) pyridine] at 0.55 kg/ha was applied in the fall and spring on soils of three types. Addition of nitrapyrin to fall‐applied NH4+significantly increased grain yield and grain protein. Grain protein was sometimes increased when nitrapyrin was applied with NH4+in the spring. Grain protein content was increased by N and nitrapyrin and from 10 to 33%. Protein generally continued to increase even after the maximum yield had been reached. The mineral composition of leaves was more dependent on soil type than on N treatment. The minerals K, Ba, and Mn were higher, and Ca, Mg, and A1 were lower in plants grown in Tracy sandy loam (Ultic Hapludalfs, coarse‐loamy, mixed, mesic) than in those grown in either Runnymede loam (Typic Argiaquolls, fine‐loamy, mixed, mesic) or Chalmers silty clay loam (Typic Haplaquolls, fine‐silty, mixed, mesic) soils. The concentrations of minerals in plants were similar with fertilizer treatments and time of application. Zinc was the only mineral in plants that significantly increased when nitrapyrin was added to NH4+. Nitrification inhibitors can effectively reduce N losses without adversely affecting the uptake of other minerals or the mineral composition of corn leaf tissue.

Large overwinter leaching and denitrification losses of fall‐applied N are common in many Corn Belt soils cropped to wheat (Triticum aeslivumL.). These losses decrease the utilization efficiency of N fertilizers, lower crop yields and quality, necessitate multiple fertilizer applications, and predispose wheat to several soil‐borne diseases. This study was conducted to determine if inhibiting nitrification of fall‐applied ammoniacal fertilizers would reduce N losses and be a practical alternative to multiple fertilizer applications in maintaining crop yield, quality, and tolerance to disease. We tested the effectiveness of a specific nitrification inhibitor, Z‐chloro‐6(trichloromethyl)‐pyridine (nitrapyrin), in reducing losses of fall‐applied NH4+sources of N in four Indiana soils of varying texture. The field experiment was conducted over a 5‐year period by comparing the growth, disease incidence, grain protein, and yield of wheat in field plots receiving anhydrous ammonia, urea, or ammonium sulfate plus nitrapyrin with wheat production in plots treated with these N sources without the inhibitor. Calcium nitrate was used in some studies to provide a source of N exhibiting high potential for loss. Inorganic N analyses of soil showed that severe loss of N frequently occurring as a result of fall application of N may be markedly reduced by using a nitrification inhibitor. Wheat yields were increased as much as 40% (average increase was 14.7%) as a result of applying 0.55 kg of nitrapyrin/ha with fall‐applied NH4+fertilizers. Yields obtained with fall‐applied N plus nitrapyrin were similar to those observed with a split‐application (25% fall—75% spring) of N without the inhibitor. Fall application at 44 kg N/ha plus nitrapyrin resulted in yield similar to those with 88 kg N/ha without the inhibitor. Inhibition of nitrification of fall‐applied NH4+also increased protein content, minimized N loss from the up per soil profile, and reduced the severity of fungal root and crown rots. Nitrification inhibitors added to fall‐applied NH4+should provide a practical alternative to multiple fertilizer applications for maintaining the yield, quality, and disease tolerance of wheat grown in the Corn Belt.

The objectives of this study were to determine the effects of soil pH, soil moisture tension, sludge application rate, incubation temperature, and nitrification inhibitor on N transformations in soils amended with an 15N‐labeled sewage sludge. Less than 0.1% of added sludge‐N was lost from any of the samples due to NH3volatilization. Nitrification rates were faster in sludge‐amended soils as compared to nonamended acidic soils treated with NH4+‐N. Adding calcareous sewage sludge to acid soils produced a more favorable pH for nitrification. Nitrification was faster in sludge‐amended soil having an initial pH of 7.5 than in samples at pH 6.0 or 5.3. Nitrite‐N accumulated to levels of 100 µg/g in sludge‐treated soils with high pH values (∼ 7.5). Nitrification proceeded at a faster rate in sludge‐amended soils adjusted to −0.25 and −0.5 bar moisture tension than in soils at −1 bar. Nitrification rates were not greatly affected by sludge application rate, although more time was required for complete nitrification of greater quantities of NH4+‐N. Nitrapyrin inhibited nitrification for 112 days, after which nitrifying ability recovered. Temperature was the only factor evaluated which markedly affected mineralization of sludge‐organic N and immobilization of added inorganic‐N. The rates of both mineralization and immobilization increased as temperatures increased. At the end of 168 days of incubation at 21°C, 40% of added sludge‐organic N was mineralized in silt loam soils, but up to 26% of added NH4+‐N was immobilized. There were only small net changes in inorganic‐N concentrations in sludge‐amended soils after 168 days of incubation.

Predictions of soil erodibility factors for selected clay subsoils were studied in relation to physical and chemical properties. Erodibility factors were determined from soil erosion rates on scalped surfaces during a series of simulated rainstorms. Subsoils were analyzed for their textural, chemical, and mineralogical composition. A predictive model, derived from previously gathered data of 46 surface soils, was used to determined the significance of soil properties in predicting subsoil erodibility. Weighted linear regression analysis using data from surface soils of the test model and seven selected subsoils indicated that a textural parameter and the percent of iron plus aluminum extractable with citrate‐dithionite‐bicarbonate (CDB) were significant prediction properties of erodibility for these clay subsoils. Multiple linear regression yielded a prediction equation with a coefficient of multiple determination of R2= 0.90.

Randomized complete block design field experiments were conducted to determine the effects of rates and methods of liquid swine manure application on volatile NH3‐N losses from cropland. In addition, a greenhouse study was conducted to determine the effect of wind on the rate of NH3‐N volatilization from soil and the accuracy of NH3‐N loss measurements under field conditions. A partially closed system was utilized to directly collect volatilized NH3‐N from microplots. The NH3‐N collection system did not accurately estimate volatile N losses when windy conditions existed as often encountered in the field. Using direct measurement of NH4+‐N in waste before and after exposure to the atmosphere to correct for the low estimates of NH3‐N loss under field conditions, an average of 48.1% of the volatilized N was collected under greenhouse conditions with relatively constant temperature and wind. The rate of NH3‐N loss from manure increased with increasing temperature and air movement. The proportions of the applied NH4+‐N lost as NH3‐N during a 3.5‐day sampling period in the spring from swine manure (pH 6.4) applied to soil (pH 6.4) and corrected for the effect of wind were: 14.0%, 12.2%, and 11.2% for the 90, 135 and 180 metric ton/ha, respectively, of surface applied liquid swine manure; 2.5% for both the 90 and 180 metric ton rates, respectively, of injected liquid swine manure; 14.7% for surface applied urea fertilizer (168 kg N/ha); and 65.8% of the applied NH4+‐N from swine manure surface applied (90 metric tons/ha) on a plastic liner. Fresh swine manure (pH 7.8) surface applied at the rate of 135 metric tons/ha on greenhouse loam soil (pH 7.0) lost 82.5% of the applied NH4+‐N in an 8‐day sampling period.

Distribution and forms of the metals cadmium (Cd) and zinc (Zn) in sediment and the possible significance of a die‐off of the aquatic macrophyte Potamogeton crispusin Cd cycling in a metal‐contaminated lake were studied. Metal levels in the upper 5 cm of lake sediment ranged from 2.54 ppm Cd and 115 ppm Zn in an uncontaminated area of the lake to 805 ppm Cd and 6,120 ppm Zn near the entrance of a metal‐bearing ditch to the lake. Evidence of metal contamination existed at a depth of 30 cm in sediments in contaminated areas of the system. Dominant forms present in the sediment were the carbonate for Cd and carbonate and organic for Zn. Analysis indicated Cd levels as high as 89.6 ppm in P. crispusin the lake with a maximum burden of 1.5 kg Cd held by the lake's P. crispuspopulation. Release of the total amount could raise water concentrations by a maximum of 1 µg/liter.

A 2‐year field experiment was conducted to study the effects of salt (0.2 and 0.5%) in swine rations, liquid waste handling systems (aerobic and anaerobic), and application rates on the recycling of swine wastes to Fox silt loam and Chalmers silt loam soils cropped to corn (Zea maysL.). Liquid swine waste (1.8 to 3.0% dry matter) was applied annually at rates of 45, 90, and 134 metric tons/ha. The high rate provided an average of 378 kg N, 113 kg P, 163 kg K, and 42 kg Na per ha. Check and inorganic fertilizer (168 kg N/ha, 56 kg P/ha, 112 kg K/ha) treatments were included. Soil Na, nitrate N, and extractable P concentrations increased with increasing waste application rates. Soil electrical conductivity was not affected by waste application rate. The effects of dietary salt levels and waste handling systems on the chemical composition of the soils were inconsistent. There was evidence for downward movement of Na, K, and NO3−in the soil profile of plots receiving waste and fertilizer. Downward movement of NO3−was observed to a greater extent in fertilizer‐treated plots than in waste‐treated plots. Under climatic conditions prevailing in this study, 2 years of waste application had no detrimental effects on the chemical composition of the two silt loam soils. Soil application of waste resulting from different dietary salt levels and waste handling systems resulted in similar corn yields and leaf chemical composition. Yields were higher from plots treated with waste and inorganic fertilizer compared to the check plot. Corn yields increased with increasing rates of waste application up to the 90‐metric tons/ha rate, then leveled off. Nitrogen, P, and K concentrations in corn ear leaf tissue increased with increasing waste applications.

Organic components in sewage sludges were extracted with nonaqueous solvents (hexane and methanol) and characterized by chromatography, infrared spectroscopy, and mass spectrometry. On the average, nonaqueous solvent soluble compounds represented 10.6% of sludge dry weight (24.8% of ash‐free dry weight) and contained 36% of the total organic C in sludge. Major compounds in nonaqueous solvent extracts included two different waxes, one phenolic fatty acid ester, and a glyceride fatty acid. Significant amounts of dibutyl phthalate, di(2‐ethylhexyl)phthalate, and butyl benzyl phthalate were also present in sludges. The presence of fats, waxes, and oils was expected; however, the presence of phthalate esters in sludges has apparently not been previously reported. The types of phthalate esters in sludge suggest that they are derived from industrial inputs to the municipal sewage treatment system. Polychlorinated biphenyls, polybrominated biphenyls, or chlorinated hydrocarbons were not detected in any of the sludges examined.

Effects of Cu levels in liquid swine manure were studied for 5 y on corn (Zea maysL.) and Crosby silt loam soil (Aerie Ochraqualfs). Pigs housed on slatted floors above pits were fed 16% crude protein corn‐soy diets with either 0, 125, or 250 mg/kg of supplemental Cu as CuSO4. Swine manure (3.2–5.2% dry matter) collected from the anaerobic pits was surface‐applied annually to soil at rates of 90, 180, and 270 t/ha for 4 y. No manure was applied the fifth year to determine the effects of residual nutrients. Check and inorganic fertilizer (168 kg N/ha, 56 kg P/ha, 112 kg K/ha) treatments were also included. Supplemental CuSO4in the swine diet increased Cu levels in manure and consequent Cu application to the soil. Copper‐enriched manure increased the 1NHCl‐extractable Cu in the upper portion of the soil profile (0–31 cm), but not at lower depths. High Cu applications from manure did not elevate plant leaf Cu concentrations, and did not adversely affect corn yields. Corn yields and leaf composition were not affected by rate of manure application since crop nutrient requirements were exceeded. Applied K and NO3−‐N moved downward in the soil profile, but a majority of these nutrients in soil were depleted by the end of the study. In contrast, applied P accumulated in the upper soil profile (0–31 cm). Application of liquid swine manure from pigs fed a high level of CuSO4over a 4‐y period at the rates used in this study did not lead to excessive soil accumulation or enrichment of corn tissue with Cu.

A 6‐yr field experiment was conducted to determine the effects of liquid and solid dairy (Bos taurus) manure applications on a Crosby silt loam (Aerie Ochraqualfs) soil cropped to corn (Zea maysL.). Liquid manure at rates of 112, 224, and 336 Mg ha−1and solid manure at rates of 34, 67, and 101 Mg ha−1were spread annually for 5 yr. No manure was applied the 6th yr, but the soil was cropped to determine residual nutrient effects. Check and inorganic fertilizer treatments were also included in the study. Manure addition increased corn yields when compared to the check (no fertilizer). There were variable weather conditions and nutrient concentrations of the manure sources, and the manure application rates were relatively high. Corn yields were as great or greater from plots supplied with manure and manure slurries as those supplied with commercial fertilizer. Over the 5 yr of manure application, the 224 Mg ha−1rate of liquid manure and the 67 Mg ha−rate of solid manure results in maximum corn yields that were 1% higher than commercial fertilizer. Accumulations of nutrients in the soil from high liquid manure application rates (224 and 336 Mg ha−1) increased corn yields during the residual cropping year. Corn leaf N and P concentrations tended to reflect N and P rates applied with the manures and the fertilizer treatment compared to the check, but not consistently each year. Source of manure had little affect on corn leaf composition. Soil P, K, and Na increased with each additional year of manure application and tended to increase with higher application rates. Extractable P accumulated in the upper profile of soil, whereas exchangeable K and Na increased at lower depths in the soil profile, especially with the highest manure application rates. Based on this study, both solid and liquid dairy manures are valuable sources of nutrients for corn production; however, they are less efficient than commercial fertilizers when comparing equivalent nutrient levels and when they are applied to the soil surface. Excessive application of either manure source causes potential for considerable groundwater pollution.

Increases in the price of N fertilizers encourage farmers to utilize alternative sources of nutrients such as sewage sludges and animal manure when the wastes are available. However, a portion of the applied N may be lost by leaching and/or denitrification after organic N and NH +4‐N in the waste is converted to NO ‐3by ammonification and nitrification. One way to reduce leaching and denitrification losses is through the use of a nitrification inhibitor. Therefore, field experiments were conducted during three growing seasons to evaluate the effects on corn (Zea maysL.) grain yield and plant composition of mixing nitrapyrin [2‐chloro‐6(trichlormethyl)pyridine], a nitrification inhibitor, with liquid swine (Susspp.) manure applied to a silty clay loam (fine‐silty, mixed, mesic, Typic Haplaquoll). Nitrapyrin was added to swine manure at rates of 0, 25, and 50 mg L−1, and the swine manure was soil injected in bands during the fall or spring prior to corn planting. Corn grain yields, ear leaf N levels, and grain N concentrations were measured. In 1978, the addition of nitrapyrin (at a rate of 50 mg L−1) to liquid swine manure springapplied at a rate of 49 Mg ha−1(154 kg available N ha−1) significantly increased grain yield, but not tissue N levels when compared to plots receiving only manure. Yields obtained from plots treated with manure (49 Mg ha−1) plus nitrapyrin were similar to those from plots receiving swine manure at a rate of 110 Mg ha−1(345 kg available N ha−1) without nitrapyrin or from 134 or 180 kg urea N ha−1. During the 1979 and 1980 growing seasons, the addition of 25 or 50 mg nitrapyrin L−1of swine manure applied at rates of 31 to 60 and 38 to 60 Mg ha−1, respectively, in the fall significantly increased yields as compared to plots receiving waste without the inhibitor. In 1979 and 1980, addition of nitrapyrin to swine manure applied in the spring at rates of 63 and 78 Mg ha−1(161 and 286 kg available N ha−1, respectively) had no effect upon corn yield. However, in 1980 the addition of 50 mg nitrapyrin L−1to manure applied in the spring at a rate of 44 Mg ha−1(159 kg available N ha−1) significantly increased yields as compared to plots receiving waste without the inhibitor. Large losses of applied N apparently occurred following fall applications of manure. Based upon yield results of manure treatments it is likely that nitrapyrin was effective in reducing losses of applied N and, thereby, increased corn yields by maintaining adequate levels of available N in the plant rooting zone throughout the growing season

High rates of N loss have been observed from N fertilizers applied directly on the surface in no‐till corn (Zea maysL.) production systems. Field experiments were conducted at four locations over a three‐year period to determine what effects N source and N placement had on N losses in both no‐till and conventional till corn production systems. Soils used were: Stoy loam, an Aquic Hapludalf; Clermont silt loam, a Typic Ochraqualf; Avonberg silt loam, an Aeric Fragiaqualf; Chalmers silty clay loam, a Typic Argiaquoll; and Lyles fine sandy loam, a Typic Haplaquoll. Nitrogen sources used were anhydrous ammonia (NH3), urea‐ammonium nitrate solutions (UAN), solid urea and solid ammonium nitrate (NH4NO3). Placement variables used were injection of NH3and UAN 20 cm below the soil surface and broadcasting UAN, urea and NH4NO3on the soil surface with no incorporation. Nitrogen rates used were 0 and 165 kg N/ha. Injecting NH3, or UAN below the surface resulted in consistently higher corn grain yields than applying UAN, NH4NO3or urea directly on the soil‐residue surface. Percent N in leaf and grain also reflected an increase in N use efficiency with subsurface N placement. Percent N in leaf was significantly higher where NH3or UAN were injected as compared to UAN or urea surface applied.

In an attempt to reduce ammonia (NH3) losses from surface applied urea to ultimately increase plant N use efficiency, a field experiment was conducted to compare the effects of six phosphoroamide urease inhibitors on NH3volatilization from urea surface applied to no‐till (NT) and conventionally tilled (CT) soils. Urea prills (200 kg N ha−1) with and without phosphoroamide inhibitors (4.0 kg a.i. ha−1) were broadcast on the surface of microplots. Ammonia evolution was measured using a semiopen‐static system in which the volatilization chambers were moved periodically to compensate for soil environmental changes induced by the enclosures. Environmental and soil conditions affected the cumulative and daily losses of N. Losses were greater and more rapid under warm, moist soil conditions than hot and dry conditions. The low specific humidity during the hot, dry conditions prevented complete dissolution of prills until 6 d after application thus reducing hydrolysis and NH3volatilization. Phenylphosphorodiamidate (PPD) most consistently reduced cumulative NH3losses on NT and CT. Ammonia loss with the addition of PPD was 10 to 54% of the NH3loss with unamended urea in three of four tests. Trichloroethyl phosphorodiamidate and N‐(diaminophosphinyl)‐cyclohexane were the only other compounds to significantly reduce NH3losses compared to unamended urea, but these compounds were effective in only one‐half the tests. Both field and laboratory studies showed significantly greater NH3losses from urea applied to residue covered soil than to bare soil. Addition of PPD or thiophosphoric triamide to residue reduced N losses to 43 and 39% of applied urea‐N, respectively. The effectiveness of PPD in retarding NH3losses was decreased as the soil pH increased from 5.6 to 7.2.

Several methods for preserving the levels of soluble inorganic phosphorus (SIP), ammonium, and nitrate in surface runoff, tile drainage water, and river water were evaluated. The best overall technique for preservation of water samples for P and N analysis appeared to be storage at subzero temperatures. The SIP concentration in samples was also stabilized by addition of HgCl2(40 mg/liter) and storage at 4C; however, the ammonium and nitrate levels in samples were not preserved for long periods of time (12 weeks) by this technique. The soluble inorganic N levels in water samples were preserved by addition of phenylmercuric acetate (20 mg/liter) and storage at 4C, but use of this procedure increased the SIP concentration in some samples during storage. Storage of samples at 4C or 23C without addition of a chemical preservative resulted in large changes in soluble inorganic P and N contents.

The effects of environmental and procedural factors (e.g., aeration, size of sample, water/sediment ratio, nitrate concentration, glucose addition, temperature, and sterilization) on denitrification in lake and reservoir sediments were evaluated by incubating nitrate‐amended natural sediments in the laboratory. The standard laboratory procedure adopted for denitrification studies involved the incubation of small samples of sediment (undried) after addition of a nitrate solution. Incubations were conducted at 15C in polypropylene centrifuge tubes. Denitrification in sediment‐water samples was not enhanced by continuously purging samples with helium to create artificial anaerobic conditions. Experiments showed that denitrification rates in sediments could be satisfactorily measured using wet sediment (0.5 g solids) treated with 5 ml of 100 ppm nitrate‐15N solution and incubated for 5 to 10 days. The small sample size facilitated sample preparation, extraction of inorganic forms of N and micro‐Kjeldahl analysis of sediment. Even though glucose additions enhanced denitrification by 25 to 30%, unamended sediments contained sufficient available organic‐C for near maximal rates of denitrification. Denitrification in sediments increased with increasing temperature over the range of 5 to 23C. However, significant denitrification occurred at temperatures as low as 5C. Nitrate was not lost from sterilized sediment samples, therefore, the nitrogen transformations observed in unsterilized sediment samples were mediated by biological mechanisms. The evaluation of factors affecting denitrification in sediment shows that the environmental conditions likely to exist in natural sediments are suitable for denitrification. Anaerobiosis and the high organic matter of most sediments create an ideal environment for microbial denitrification. The levels of nitrate in surface water may in part be controlled naturally by denitrification in sediments.

A simple, precise, and rapid method for estimating total N (to include nitrate and nitrite) in natural water is given. The proposed method involves evaporation of the water sample, pretreatment of the evaporated sample with reduced iron and H2SO4to reduce nitrate to ammonium, and subsequent Kjeldahl digestion of the sample to recover organic N. Evaporation, pretreatment, and digestion of samples are accomplished in Folin‐Wu nonprotein tubes. Ammonium in the digest is estimated by steam distillation and subsequent titration. Evaluation of the proposed method revealed that the recovery of nitrate N and organic N in samples was affected by the amount of reduced iron added (200 mg was satisfactory), by the brand of reduced iron used (several preparations were satisfactory), and by gently boiling the sample with reduced iron and H2SO4prior to digestion. The proposed method was effective in recovering nitrate N and organic N from water solution over a wide range in concentration and the method was successful in recovering nitrate N and organic N added to filtered and unfiltered river and pond water samples. The precision of the proposed method was satisfactory for total N analysis of water samples, and the method appears adequate for estimation of total N in most water and waste water samples.

A cooperative study was conducted with Pennsylvania State University to assess the effects of wastewater irrigation on the status of soil phosphorus. The major objectives of the research were to evaluate the influence of wastewater irrigation on changes in soil organic carbon, nitrogen, and phosphorus and the sorption of orthophosphate (P). Soil samples were obtained in 1974 and 1975 from Hublersburg silty clay loam cropped to corn (Zea maysL.), Reed canarygrass (Phalaris arundinaceaeL.), or a mixed forest and from a Morrison sandy loam with a mixed forest stand. The sites had been irrigated with secondary effluent for 11 to 12 years. Soil analyses indicated that the majority of phosphorus added to soils during wastewater irrigation remained in the upper 30 cm of the Hublersburg clay loam soil. In contrast, appreciable amounts of P had leached to the 30 to 60-cm depth in the Morrison sandy loam. The equilibrium phosphate concentration (EPC) increased markedly at the 0 to 15-cm depth as a result of wastewater irrigation, due to sorption of P added in the wastewater. As expected, the maximum P sorption capacity of soils was decreased by wastewater irrigation. A comparison of soluble P levels in leachate samples collected in the field at a 120-cm depth with soluble P predicted by EPC measurements indicated that laboratory measurements overestimate the ability of a soil to remove P from wastewater. Thus, wastewater may not interact with all potentially available P sorption sites in soils. The EPC and P sorption capacity of soils irrigated with wastewater was reduced by extracting soils with oxalate and citrate-dithionite-bicarbonate. These results indicated the significance of hydrous iron oxides in P retention by soils irrigated with wastewater.

Increased nitrogen loss from leaching, denitrification, or volatilization with reduced or no-till farming may offset potential energy savings from reduced field operations. Nitrification inhibitors have effectively reduced N losses in conventional tillage and may increase the energy efficiency and yield resulting from N applied to no-till corn. For 3 years, we studied corn produced by no-till farming to determine the effects of inhibiting nitrification of spring-applied N with nitrapyrin or etradiazole on corn yield and N use efficiency. Low grain yields obtained without N fertilization indicated that only low levels of residual or mineralizable N were available for corn growth. The importance of incorporating N in the soil was indicated, because plants fertilized with 28 percent N solution injected into soil produced 20 percent more grain than plants fertilized with broadcast 28 percent N or urea. The highest grain yield was achieved with anhydrous NH3. Plants fertilized with surface-applied N fertilizers showed symptoms of N deficiency by 30 days postpollination. Inhibiting nitrification of injected NH3or 28 percent N solution generally increased corn yields compared with N without the inhibitor. Nitrification inhibitors have a good potential to improve N use efficiency and grain yields by reducing losses of applied ammoniacal N in no-till corn production systems.

Large overwinter losses of fall‐applied fertilizer N from midwestern U.S. soils occur through leaching and denitrification. These losses result in decreased efficiency in the utilization of applied N and often in lower crop yields. Of the various management techniques available to reduce N losses, previous studies with spring‐applied N suggested that inhibiting nitrification of applied ammonium with specific chemicals appears to be most compatible with current fertilization and crop production practices. We tested the effectiveness of a specific nitrification inhibitor, 2‐chloro‐6‐(trichloromethyl)pyridine (nitrapyrin), in reducing losses of fall‐applied N by comparing the growth, disease incidence, and yield of corn growing in field plots receiving anhydrous ammonia with those treated with anhydrous ammonia containing the inhibitor. Three field experiments on two soil types (Typic Argivdoll coarse‐loamy, mixed mesic and Vertic Halpla‐quoll fine, montmorillonitic, mesic) demonstrated that inhibition of nitrification of fall‐applied ammonium markedly increased grain yields and grain protein and decreased the incidence of stalk rot in corn. Corn yields were increased as much as 207% (average increase was 68%) as a result of applying 0.55 kg of nitrapyrin/ha with fall‐applied anhydrous ammonia when compared to yields obtained with anhydrous ammonia without the nitrification inhibitor. In all experiments, stalk rot incidence in corn was reduced as a result of inhibition of nitrification — the reductions varied from 60 to 96%. In two experiments, grain protein content was increased by 7 to 38% as a result of application of nitrapyrin with fall‐applied N. The results of this study indicate that severe losses of N may occur as a result of fall application of N fertilizers and that these losses may be markedly reduced by using a nitrification inhibitor to minimize the formation of nitrate. The increased yield and grain protein obtained from nitrapyrin addition likely resulted from greater availability of N in nitrapyrin‐treated plots. The reduction in stalk rot may have resulted from altered N metabolism in plants growing in nitrapyrin‐treated plots because of the uptake of substantial amounts of ammonium. This was indicated since stalk rot was reduced by nitrapyrin in plots which were not under N stress. Another explanation for reduced stalk rot may reside in the fact that nitrapyrin‐treated plots had more vigorous plants than plots not receiving the nitrification inhibitor. The data also suggest that N application rates used for corn production may be decreased with no loss in yield if a nitrification inhibitor is used to minimize losses of applied N.