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The purpose of this study was to determine why N fertilizer recovery by Coastal bermudagrass (Cynodon dactylonL.) is lower on swelling clay soils than on coarse‐textured soils. The disposition of N fertilizer applied to Coastal bermudagrass in the field over two growing seasons was determined by applying 560 kg N/ha as Ca(NO3)2tagged with 7.599 atom % 15N to a field microplot during 1974 and measuring various components of the N balance. Plant uptake of residual N was measured during 1975. Forty‐nine percent of the applied N was recovered in harvested forage in 1974. About 40% of the applied N remained in the soil as residual N at the end of 1974. About 10% of the N was unaccounted for, indicating that denitrification losses were no more than 10% of the applied N. Most of the residual N at the end of the first growing season was immobilized N or was present in the root system of the grass. Immobilization is, therefore, a major factor causing low recovery of applied N by Coastal bermudagrass on swelling clay soils. Moreover, since only 17% of the residual N was recovered in forage during 1975 (7% of the N applied in 1974), most of the immobilized N was not available the following year.

A system is needed to measure ammonia volatilization from N fertilizer applied under field conditions. This study was undertaken to develop a device for making these measurements and still maintain a field environment. The basic system developed consists of a vacuum pump, a chemical trap to capture ammonia, and the volatilization chamber. The volatilization chamber consists of a steel cylinder 21.8‐cm I.D. by 15‐cm long that is forced into the soil with its top flush with the soil surface to provide a microplot. The lid assembly attached to the cylinder includes a hinge and reversible electric motor that allows the lid to be automatically rotated from the microplot. The volatilization chamber was designed with the removable lid so that the lid is closed only for short intervals during the day while ammonia loss is measured. The total ammonia loss is calculated by integrating the rates of loss over time. Between measurements, the lid is open to allow normal environmental conditions of temperature, wind movement, etc., on the micro‐plot. The volatilization chamber has five air intake ports and one exhaust port. Ammonia loss was unaffected by air flow rate if air movement through the chamber exceeded 15 exchange volumes/min. Our complete system consisted of eight volatilization chambers with a system of multiple chemical traps that can operate automatically without attention for 24 hours. When tested in the field, duplicate measurements of ammonia loss from ammonium sulfate agreed quite closely, both in the rates of loss and the total ammonia loss. In another test, ammonia loss from ammonium chloride agreed reasonably well with other laboratory results.

Low recoveries of N fertilizer by crops on Houston Black clay prompted this investigation. Our objectives were to determine how much fertilizer nitrate can be biologically immobilized under field conditions when fertilization exceeds crop requirements and to determine when immobilization occurs during the growing season. Calcium nitrate tagged with 9.6 atom % 15N was applied to field microplots at 328 kg N/ha and grain sorghum (Sorghum bicolorL.) was planted in rows across each microplot. The various components of the N balance were measured by sampling microplots at different times during the season. Only 2.1 kg N/ha was immobilized during the first 47 days after fertilization and planting. The rate of immobilization increased rapidly during the next 60 days and an additional 60 kg N/ha was immobilized. This increase was apparently in response to an increase in soil temperature above 22°C. About 91% of the fertilizer N was recovered, indicating that no more than 9% was denitrified, in spite of ample water that was received as rain or irrigation water during the study. A net immobilization (an increase in soil organic N relative to an unfertilized plot) of 53 to 73 kg N/ha was measured on the fertilized plot. This net immobilization suggests that the organic N content of swelling clay soils that have historically been subjected to exhaustive cropping may increase slowly and gradually reach a higher equilibrium level due to N fertilizer use.

The effects of temperature and rate of application on NH3‐N volatilization from NH4+salts applied to the surface of a calcareous soil were investigated in the laboratory. Total NH3‐N losses were only slightly influenced by temperature over a broad range of NH4+‐N application rates with a precipitate forming NH4+compound such as (NH4)2SO4in a calcareous soil. The rates of NH3‐N loss were highly influenced by temperature. High temperatures increased the initial rates of NH3‐N loss although they were proportionally reduced at later stages. The lowest temperature resulted in the lowest initial NH3‐N loss rate but became highest for the last 76 hours. Total ammonia nitrogen losses were dependent on the rate of NH4+‐N application. The quantity of NH3‐N loss varied from 19 to 50% of the applied NH4+‐N at 33 to 550 kg NH4+‐N/ha, respectively. The increasing temperature increased losses of NH3‐N from NH4NO3which does not form precipitates with CaCO3or appreciable (NH4)2CO3. In 100 hours, NH4NO3lost 14, 18, and 26% of the applied NH4+‐N at 12, 22, and 32C, respectively. Both the total 100‐hour NH3‐N losses and rates of NH3‐N loss were increased by increased temperatures; however, the percent of NH3‐N volatilized was unaffected by rates of NH4+‐N application. Ammonium sulfate losses from a noncalcareous Wilson clay loam buffered to the pH of the calcareous soil produced NH3‐N losses equivalent to NH4NO3at 12C and lower than NH4NO3at 32C. Ammonia nitrogen losses, both total NH3‐N and rates of NH3‐N loss, were similar to losses of NH4NO3from the calcareous soils. Therefore in the calcareous Houston Black clay the NH3‐N loss caused by reaction of (NH4)2SO4with CaCO3ranged from 0 to 70 or 80%. Regression equations were developed that predict NH3‐N losses at certain temperatures, time, and rate of NH4+‐N application.

This study was conducted to evaluate the influence of overburden pressure on the movement of water and Cl‐through short undisturbed cores of swelling clay soil. When overburden pressure was removed from the cores, saturated flow rates increased. Subsequent miscible displacement studies revealed that the percent soil water excluding Cl‐was also reduced. When soil cores were loaded with overburden pressure, the amount of soil water excluding Cl‐was approximately 50%. When overburden pressure was removed, the amount of soil water excluding Cl‐was 33%, about the same value as measured in disturbed soil cores of approximately the same water content. Differences in the quantity of soil water excluding Cl‐between loaded and unloaded cores were due to an interaction between soil structure and the negative charge on the clay in the loaded cores. Apparently, when overburden pressure was removed, smaller pores increased in diameter, which allowed Cl‐to diffuse more freely into these spaces.

Factors influencing ammonia (NH3) volatilization from surface‐applied urea have been studied extensively; however, almost all research has been done in a manner that modifies the environment compared to field conditions. Results from such studies, therefore, may incorrectly assess actual losses in the field. Our objective was to evaluate the magnitude of NH3volatilization and how soil temperature, soil water, and other environmental factors affected rates of loss. Three studies were conducted to assess the volatilization of NH3from surface‐applied urea, two on a silt loam and one on a very fine sandy loam soil. A mass‐balance micrometeorological method, which produces very minimal disturbance of the natural environment was used in all studies. Diurnal patterns of NH3loss, which coincided with the fluctuations in surface temperature and water content, were found in each study. In all studies, loss followed most closely the pattern of urea hydrolysis. Urea hydrolysis in the surface soil was slowed by dry conditions and approached zero when the soil was near “air dryness.” Rainfall of 0.86 cm did not prevent further NH3loss from Muir silt loam soil (fine‐silty, mixed, mesic Pachic Haplustolls). Three simulated rainfalls with 0.5 cm of irrigation separated by 3 and 4 days did not curtail loss from Haynie very fine sandy loam soil (coarse‐silty, mixed, mesic Typic Udifluvents), but rather enhanced the rate of volatilization, probably due in part to an increased rate of urea hydrolysis.

Estimating the loss of N fertilizer as ammonia from the ground to the atmosphere via the integrated horizontal flux method (IHF) generally requires measurement of the mean atmospheric ammonia density and the mean wind speed at five or more heights. Using acid traps as a means of measuring ammonia density at that many heights over long periods of time proves laborious, and a way of reducing the number of heights is desirable. This paper presents an application of an analytical solution of the diffusion equation for local advection to the estimation of the loss of ammonia from a small circular (20 m radius) plot fertilized with 200 kg N/ha urea‐ammonium nitrate solution. Predicted ammonia density profile shapes agree well with those measured at the center of the plot. The estimated fluxes obtained from the “theoretical profile shape” solution (TPSP) show much less variation than those from a recently proposed single‐height method (TPSW), when compared with estimates from the IHF method using mean wind speed and mean ammonia density at five heights. The ratios of FTPSP/FIHFwere found to be generally > 1 under unstable atmospheric conditions and < 1 under stable conditions. The advantages of TPSP over TPSW are that samples may be taken where the error to magnitude of measurement ratio is smaller and the solution is simple to calculate for any size plot, provided an estimate of atmospheric stability may be made.

A quantitative description of pH changes in N fertilizer application zones is needed to predict the degree of NH3formation in the soil solution. In particular, the pH changes following surface application of urea determine in part the degree of NH3formation and possible loss by volatilization. The objectives of our study were to compare the rise in soil pH following addition of urea and NH4OH to soil, and evaluate the importance of inorganic C reactions to any differences in the rise in pH caused by the two respective N sources. Titration curves with urea or NH4OH as a base were used to determine differences in the patterns of pH change. Up to pH 8.2, soil pH was raised identically by NH4OH and urea that had been completely hydrolyzed. Above pH 8.2, urea was less effective than NH4OH in raising soil pH. The lower effectiveness of urea was due in part to the urea‐C not forming CO2but remaining as HCO−3and CO2−3in the soil solution. Part of the CO2−3precipitated as CaCO3when enough urea was added to raise soil pH to 8.8. At a lower application rate of urea, which resulted in a soil pH of 7.15, no CaCO3was detected. These results demonstrate the importance of inorganic C from urea hydrolysis in providing resistance to a pH increase above pH 8.2 in concentrated fertilizer application zones.

Methods to estimate the amount of N mineralized from soil organic matter are needed for accurate fertilizer recommendations. We conducted laboratory and field studies to evaluate the method of Stanford and Smith for predicting N mineralized under field conditions. Soil samples were incubated to determine their N mineralization potentials and first‐order rate constants of mineralization. To predict N mineralized in the field, the rate constants of mineralization were adjusted by soil temperature, and the amount of N mineralized predicted with the N mineralization potentials and adjusted rate constants were further adjusted by soil water content. Nitrogen mineralized in the field was measured in sorghum [Sorghum bicolor(L.) Moench] plots established on Haynie (coarse‐silty, mixed, calcareous, mesic Mollic Udifluvent), Kahola (fine‐silty, mixed, mesic Cumulic Hapludoll), and Richfield (fine, montmorillonitic, mesic Aridic Argiustoll) soils in 1983 and 1984. Nitrogen mineralized was also measured in fallow plots on Haynie and Wymore (fine, montmorillonitic, mesic Aquic Argiudoll) soils in 1984. The method only accurately predicted the amount of N mineralized in 104 d in fallow plots on Haynie soil. In all other cases, the method significantly overpredicted by 67 to 343% the amounts of N mineralized in the field. Among possible causes for the overpredictions may be an improper soil water content factor and the drying and sieving of the samples before incubation.

Calculation of the correct nitrogen (N) fertilizer rate for a crop requires an estimate of the amount of N that mineralizes from soil organic matter during the growing season. A method proposed by Stanford and Smith for estimating N mineralization sometimes results in overpredictions which may be due to the use of disturbed soil samples. To study the effect of soil disturbance, we measured N mineralized in disturbed and undisturbed soil samples, and determined models that properly described the data for each type of sample. A double exponential model was required for disturbed samples, whereas a single exponential model was adequate for undisturbed samples. Although in general, models fitted to disturbed samples could not be used to predict N mineralized in undisturbed samples, they could be used to estimate the parameters of the single exponential model for undisturbed samples. Parameters estimated using this approach, together with daily values of soil temperature and water content, allowed reasonable predictions of the amounts of N mineralized in fallow plots on Haynie (coarse‐silty, mixed, calcareous, mesic Mollic Udifluvent) and Wymore (fine, montmorillonitic, mesic Aquic Argiudoll) soils. Parameters of the single exponential model for undisturbed samples could also be estimated from total N and clay contents of the soil. The results suggest that it may be possible to obtain accurate estimates of N mineralized in the field by estimating, instead of determining, the parameters of the single exponential model for undisturbed samples.

Urea fertilizer is often applied at the soil surface, where it hydrolyzes and can form NH3. To quantify the volatilization of NH3, the molecular diffusion of urea into the soil must be described. The diffusion coefficient of urea in soil is related to its diffusion coefficient in water, which varies with temperature. We initially regressed the value of the urea diffusion coefficient in water from the international critical tables (ICT) on temperature for the range of 10 to 20 °C. Since surface soil temperatures often fall outside this range, additional values for the urea diffusion coefficients were needed. The capillary tube method of Phillips and Ellis was used to measure the diffusion coefficient of urea in water at temperatures ranging from 0 to 50 °C. The laboratory values obtained for the diffusion coefficient of urea in water were higher, by a factor of 1.5, than the ICT values. A comparison was made between measured values of urea concentration in columns of Richfield and Haynie soils and simulated values using regression equations based on laboratory results (new) and ICT data (old). The new regression equation allowed a better agreement between actual and simulated urea concentrations in soil.

This study was prompted by the present controversy over the role that N‐fertilizer use may have in reducing water quality. Our objective was to determine the disposition of N fertilizer (enriched with 15N) applied to level (< 2% slope) Houston Black clay near the economic optimum application rate (112 kg N/ha) for grain sorghum (Sorghum bicolor[L.] Moench). Particular emphasis was placed on determining the amount of applied N which leached below the root zone at different times during and after the growing season. A large, undisturbed, field‐drainage lysimeter was used to measure leaching of NO3−‐N below the root zone. During spring 1973 94 mm of drainage water containing a mean concentration of 2.4 ppm fertilizer‐derived NO3−‐N percolated through the soil profile. At crop maturity, only 55% of the N applied the previous spring was recovered by the crop or was present in drainage water. Large amounts of N not recovered by the crop were either measured as immobilized N (20% of the applied N) or were unrecovered and assumed denitrified (17%). During fall and winter approximately 120 mm of drainage water containing 0.5 ppm or less fertilizer‐derived NO3−‐N percolated through the soil profile. These results indicate that for rainfall conditions observed in this study (minimal crop water deficit), the application N fertilizer to grain sorghum at the near‐optimum economic rate probably will not seriously reduce ground‐water quality on a swelling clay soil, even though crop recovery of applied N may be low.

Residual fertilizer N was characterized in Houston Black clay and Keene silt loam surface soils recent field microplot-N balance studies involving liberal (328–560 kg N/ha) 15N-labeled rates. Results indicate residual N is readily distributed in all the organic and inorganic soil forms, even after the first cropping season. An equivalent distribution of the residual N with the indigenous soil N, however, had not occured after three years. During this period the residual N was more than twice as susceptible to mineralization as the soil N. Most of the residual N was incorporated in amino acid N-forms.

Leaching losses of applied NO3−‐N and Cl−from a swelling clay soil were measured using an undisturbed field drainage lysimeter. Nitrate‐N and Cl−, applied at 110 and 279 kg/ha, respectively, were detected in drainage water collected at a depth of 125 cm after the first large rainstorm. Applied fertilizer was leached when percolating rainwater carried the applied materials through large connected pores, bypassing other soil water inside soil structural units. Even though applied fertilizer began to be lost with the first rainstorm, concentrations of NO3−‐N and Cl−were not high until large amounts of water had drained below the root zone. For example, Cl−concentrations during the first 25 mm of drainage increased by about 7 ppm. The greatest increase in Cl−concentration did not occur until 60 mm of drainage accumulated after fertilizer application. Much more native soil nitrate was leached than soil nitrate concentrations in unfertilized plots would have indicated. The data indicate that leaching losses of nitrate from mineralization may be greater than those of applied nitrate when accumulated drainage is <50 mm following fertilizer application.

Accurate N fertilizer recommendations depend upon knowing the amount of soil organic N that is mineralized. A promising method developed by Stanford and Smith (1972) to predict N mineralized with disturbed soil samples allows for adjustment in the mineralization rate due to field variations in soil temperature and water. Recent work has indicated that undisturbed soil cores could more closely represent the field soil and its mineralization characteristics. Therefore, a method was needed to secure undisturbed soil cores in a container that would maintain their field integrity and allow them to be incubated and leached periodically as per Stanford and Smith's technique. The method utilizes a 6.3‐cm i.d. polyvinyl chloride (PVC) compression coupler to hold an undistrubed soil core. The undisturbed soil sampling device consists of a lever and anchor system, which can put pressure on a soil cutter and adjustment bar to force soil into the coupler. After a soil core is obtained from the field, the coupler is adapted so that the soil within can be leached, equilibrated to a constant water potential, and incubated. In extensive sampling of 19 soils that varied widely in clay and organic C contents, samples could be obtained rapidly if soil was near field capacity. This method of sampling and incubation was relatively inexpensive and simple, and produced data of cumulative N mineralized with time that could be fit with a first‐order kinetic model.

The purpose of this study was to determine why N uptake and forage production by tall fescue (Festuca arundinaceaSchreb.) in southeastern Kansas are greater from subsurface‐banded (knifed) than from broadcast N applications. The fate of urea N fertilizer applied to tall fescue either broadcast or banded in 1982 was determined using a urea ammonium nitrate (UAN) solution containing 15N tagged urea and measuring various components of the N balance. Plant uptake of residual urea N was measured during 1983. In 1982, 62% of the banded urea N was recovered in harvested forage, whereas only 40% was recovered in the broadcast treatment. Tagged N remaining in the soil as residual N at the end of 1982 amounted to 40 and 45% for broadcast and band treatments, respectively. Most of this residual N was not available to plants in 1983 since only 1.4 kg fertilizer N ha−1(5–6% of the residual N) was recovered in the forage. About 1% of the banded N was unaccounted for, indicating that gaseous losses (denitrification and ammonia volatilization) were about 1% of the applied urea N, whereas 23% of the broadcast urea N was unaccounted for, indicating probable significant gaseous losses. These results suggest that the improved efficiency of knifed N over broadcast N observed in southeastern Kansas may be due to reduced gaseous N losses.

A correct value for the molecular diffusion coefficient of urea in soil (Ds) is required to accurately predict urea movement in soil by molecular diffusion. In previous work, to estimate Dsin a simulation model of urea diffusion, we used an empirical equation of Papendick and Campbell that describes Dsfor a dissolved species in soil to be a product of a tortuosity factor squared, the species diffusion coefficient in water (Dw), and the volumetric water content. Comparisons of measured and computed urea concentration with depth indicated that this equation was not adequately general over a wide range of soils. The objective of this study was to modify the parameters in the equation and, if necessary, develop a new relationship to estimate the value of Dsin soils. Laboratory studies were conducted on seven soils in which the clay content ranged from 10 to 51%. Urea concentrations with depth at 48 h following surface‐application were measured and also computed using numerical techniques with an initial estimate for Dsinstead of computing it using Papendick and Campbell's equation. The Dswas modified incrementally, until the difference between computed and measured concentrations was minimized. In all seven soils, good agreement was obtained between measured and computed urea concentrations with depth. The maximum depth of urea movement occurred in Kahola soil (approx. 3.5‐cm deep), whereas least movement occurred in Crete soil (approx. 2.6‐cm deep). Nonlinear regression analysis gave a better relationship (Ds= 0.18 × Dw(Θv/porosity)2.98, R2= 0.88) when relative water content (Θv/porosity) of the seven soils was substituted for the volumetric water content (Ds= 0.73 × Dw(Θv)2.58, R2= 0.66) in Papendick and Campbell's equation.

Simulation models of fertilizer behavior in soils are potentially useful tools to improve fertilizer use efficiency. Presently, there are no satisfactory models that describe NH3retention in soils. In order to develop such a model, a better understanding of how soils retain NH3and a quantitative measure of soils' NH3retention capacity are needed. We compared soil cation exchange capacity (CEC) and several measures of soil titratable acidity for predicting the amount of NH3retained in the center of a band resulting from anhydrous NH3application to soil. The titratable acidity to pH 9 estimated with NH4OH was a much better predictor than CEC of the NH3retained. In some soils, the pH in the center of an NH3retention zone differed slightly from pH 9, resulting in some error in estimating the NH3retained. This error was greatest on a salty soil because of the small slope of the buffer curve near pH 9. We found soil titratable acidity to be stoichiometrically related on a 1:1 basis to the amount of NH3retained. Apparently, CEC is a poor predictor of the amount of NH3retained by soil because many of the cation exchange sites do not participate in a soil's capacity to adsorb NH3. Since a soil's titratable acidity to pH 9 is a stoichiometric predictor of NH3retention capacity in soils, it may be used to more easily model the properties of an NH3retention zone as affected by factors such as N fertilizer rate applied, spacing between application points, and soil bulk density.

To describe how soil properties affect anhydrous ammonia (NH3) retention, more accurate laboratory methods are needed to apply anhydrous NH3in a line source (band) and sample the resulting NH3retention zone. We developed and tested a line‐source NH3applicator and a method for sampling the resulting NH3retention zone. The applicator has a system of flow control valves and a flow meter to regulate the rate of NH3flow to an injection needle. The needle is held stationary while NH3is injected into a box of soil. The box of soil moves on a platform whose speed can be varied to change the NH3application rate. The soil sampling method was to sequentially remove concentric cylindrical cores of increasing radii centered around the line of NH3injection. Ammonia was applied to two soils with different NH3retention capacities and the resulting NH3retention zones were sampled. Accurate NH3deliveries were possible with the system described. The coefficient of variation of the platform speed was <1%. The sampling method gave N recoveries that ranged between 95 to 99%. By using the concentric ring sampling method, ammoniacal‐N concentrations of duplicate retention zones at different distances from the injection line were not significantly different. Thus, the applicator and soil sampling method proved to be both accurate and precise for studying NH3retention zones in soil.

The increased use of urea and urea‐based N fertilizers along with an increase in crops under no‐ or reduced‐tillage practices may require changes in fertilizer management practices. Surface application of urea‐based fertilizer risks the loss of some N by volatilization of NH3. Our objectives were to assess the loss of NH3and to simultaneously observe the associated N transformations and movements in the field following broadcast application of urea‐ammonium nitrate solution at a rate of 200 kg N ha−1to soil with wheat (Triticum aestivumL.) straw residue cover. Also, we wanted to characterize the factors associated with the residue that might affect loss. A micrometeorological mass‐balance method was used to measure NH3loss during two sequential field studies with different amounts of precipitation and irrigation. Volatilization losses showed diurnal patterns coinciding with fluctuations in residue temperature, residue water content, and wind speed. Cumulative NH3‐N losses were 7.6 and 16.6% of the N applied, respectively. The rate of urea hydrolysis and NH3loss were quite sensitive to the availability of water. Simulated rainfalls with 2.5‐mm sprinkler irrigation increased NH3loss. In both studies, peak volatilization rates came the 1st d after irrigation. The maximum measured rate of NH3loss was 51 µg m−2s−1(1.5 kg N ha−1h−1). Rainfalls of near 30 mm in both studies moved much of the remaining fertilizer below the 40‐mm soil depth. Wheat straw was found to have a urease activity of about 1830 mg urea kg−1h−1, a pH near 8, and a H‐ion buffering capacity of 53 mmol kg−1(pH unit)−1. These factors undoubtedly contributed to NH3loss.

Two laboratory experiments were conducted to evaluate the effects of rapid soil drying on the potential for ammonia (NH3) volatilization from urea. Urea was applied to the surface of a sandy loam soil in acrylic chambers at a rate equivalent to 200 kg N ha−1. Static traps for NH3and carbon dioxide (CO2) were added to the chambers and left in place for 48 h. Humid or relatively dry air was passed over the soil in the chambers between 48 and 72 h at rates sufficient to not inhibit NH3volatilization. Concentrations of NH3in the airstream leaving the chambers was monitored during this period. At 48 and 72 h, soil in selected chambers was sampled in 2‐mm depth increments and analyzed for pH, urea‐N, and ammonium‐nitrate (NH4+‐N). Rapid drying of the soil was found to rapidly decrease the rate of NH3loss from the soil. Drying also reduced the amount of urea that hydrolyzed during the period from 48 to 72 h to practically zero. In the surface 2 mm, the urea concentration of the chambers receiving the dry air treatment increased substantially during the period of airflow. This increase was due to the mass flow of urea towards the soil surface as water evaporated from the soil. These data indicate that the potential for NH3volatilization from urea applied to a soil that is initially moist but dries rapidly is low, if the soil water content/potential falls to a level at which urea hydrolysis is inhibited.

The influence of soil pH and soil cation exchange capacity on ammonia volatilization from surface applied ammoniacal nitrogen has been reported in previous studies. Since the hydrolysis of ureacontaining N fertilizers causes an increase in alkalinity, a soil's inherent H+buffering capacity (defined as the soil's total acidity, comprised of exchangeable acidity plus non‐exchangeable, titratable acidity), should exert a dominant influence on the maximum soil pH at the site of urea fertilizer application. The objective of this study was to demonstrate the importance of a soil's H+buffering capacity in affecting NH3volatilization from surface‐applied urea. The H+buffering capacity of two soils was increased by adding hydroxy‐Al polymers to one soil, and weak and strong acid cation exchange resins to the other soil. Care was taken to keep cation exchange capacity and initial pH close to the same on amended and unamended (control) soils. Urea was surface‐applied to amended and unamended soils and ammonia volatilization and soil surface pH were measured. The increase of H+buffering capacity of soils was found to reduce soil surface pH and NH3volatilization after application of urea. It is concluded from this work that H+buffering capacity of a soil is a better indicator of NH3loss potential than a soil's initial pH.

The positive effect of placing N (especially NH+4‐N) with P on crop growth has been demonstrated many times in short‐term greenhouse studies. Under field conditions, however, the effect has not been well defined. The present objective was to evaluate N and P placement methods on the P nutrition and final grain yield of wheat (Triticum aestivumL.) grown in the field and greenhouse. Anhydrous ammonia (NH3), urea‐ammonium nitrate solution (UAN), and sodium nitrate (SN) were N sources while liquid ammonium polyphosphate (APP) was the P source. Methods of N‐P application included: knife N‐knife P (‘dual knife’), knife N‐hroadcast P, broadcast N‐knife P, and broadcast N‐broadcast P. Two nitrification inhibitors were included in some studies. In the greenhouse, APP was labelled with 33P orthophosphate and 32P pyrophosphate to examine P uptake of its ortho‐ and polyphosphate fractions with different N‐P‐K application methods each with either a NH+4‐N or NO‐3‐N source. Dual knife N‐P applications gave higher leaf P concentrations and grain yields than other N‐P application methods in many of the field studies when ammoniacal N sources were used. Sodium nitrate dual knife applications were not as effective as dual knife applications of UAN or ammonia. The inclusion of the nitrification inhibitor nitrapyrin to dual knife treatments increased grain yield and/or leaf tissue P level in two 1978 studies, but had no effect in 1979. In the greenhouse the highest leaf P levels resulted from the banded NH3‐APP application. The banded SN‐APP application gave the second highest P uptake. This study also demonstrated that the N and APP need to be placed together, not separately in the soil. The amounts of the initial ortho‐ and polyphosphate portions of the APP absorbed by the plants seemed to be a function of fertilizer P demand and not related to fertilizer N in the same band. Including KCl in a band of APP did not affect leaf tissue P concentrations.

The objective of this study was to determine the influence of soil cation exchange capacity (CEC) and depth of incorporation on NH3‐N volatilization from NH4+‐N compounds applied to calcareous soil. This study was conducted in the laboratory on soils with a wide range of CEC. An increasing CEC resulted in decreasing NH3losses. Ammonium sulfate produced higher soil pH values and NH3losses than did NH4NO3. The pH of the soil decreased with increasing NH4NO3application rates. With NH4NO3, percent NH3‐N losses decreased with increasing application rate; however, with (NH4)2SO4, percent NH3‐N losses increased as the application rates increased. Incorporation of the NH4+‐compounds into the soil reduced NH3losses. Increasing depths of NH4+‐incorporation resulted in reduced NH3loss. Losses decreased as the CEC of soil increased. The effectiveness of soil depth in reducing NH3loss was associated with soil water content. Decreasing the soil water increased the effectiveness of soil incorporation for reducing NH3losses. Two regression equations were developed to describe NH3losses with respect to CEC, soil pH, time, NH4+‐N application rate and temperature. Correlation coefficients were 0.86 and 0.81 for (NH4)2SO4and NH4NO3systems, respectively.

In previous field studies a 46 cm spacing of preplant bands of N and P fertilizer has caused uneven growth of winter wheat (Triticum aestivumL.), with better growth immediately atop the preplant bands. Narrower spacing of fertilizer bands could improve plant growth uniformity and grain production by winter wheat. The objective of this study was to evaluate N‐P fertilizer band spacing on wheat growth and grain yield. The effect of P band spacing on fertilizer P uptake from a preplant band was studied in the greenhouse with winter wheat. Phosphorus uptake from the fertilizer band was influenced by the lateral distance from the wheat row to the P band at 33 days after planting. By 40 days after planting, however, uptake of fertilizer P was the same from bands placed 0, 10, and 20 cm from the wheat row, while P uptake was significantly less from the band placed 30 cm from the row, apparently due to another row of wheat shielding the fertilizer P from uptake. Field studies consisting of combinations of spacings of preplant bands (25, 38, and 50 cm) and rates of P fertilizer (0,6, 12, and 24 kg/ha), all with 84 kg N/ha, were conducted on winter wheat. All treatments were deep‐placed preplant band applications of liquid ammonium polyphosphate (APP, 10‐15‐0) and anhydrous ammonia (82‐0‐0). Wheat was drilled perpendicular to the direction of the preplant band application. Early season growth of winter wheat increased with increasing P rate and by decreasing the distance between preplant bands. Final grain yield, however, was influenced only by P rate, and not by P band spacing. Plant samples taken from 12.5 cm of drill row centered over the band and 12.5 cm of drill row centered between preplant bands of each treatment indicated differences between those areas in dry matter production, P uptake, spike density, and grain yield due to P rate and band spacing. Thus, more uniform growth resulted from the closer band spacing of 38 and 25 cm which could result in higher grain yields under optimum wheat production conditions.

The application of N and P fertilizers together in deep, preplant bands is an effective method of fertilizer placement for winter wheat (Triticum aestivumL.). However, it produces uneven growth of wheat with the greatest growth directly over the preplant bands. Two field studies were conducted on a Crete series soil (fine, montmorillonitic, mesic Pachic Argiustoll) to determine if the addition of N and P fertilizer banded with the seed could eliminate this uneven growth and, in turn, increase grain yields. Wheat was planted in rows perpendicular to the preplant bands so that plant and spike samples could be taken from row sections located at different distances from the preplant band. In 1980‐1981, seed‐banded fertilizer increased tillering and early dry‐matter production in all row sections. However, these increases did not translate into higher spike densities or grain yields. In 1981‐1982, seed‐banded fertilizer increased tillering and early dry‐matter production in row sections between preplant bands, which reduced but did not eliminate the uneven growth caused by preplant bands. Although significant grain yield increases were obtained in row sections between preplant bands, no significant increases in overall grain yield were found. Results indicate that the addition of seed‐banded fertilizer can increase overall early dry‐matter production and may reduce, although not eliminate, the uneven growth caused by preplant bands.

The effect of available P in subsoil on plant uptake of P from surface soil layers and consequently on fertilizer recommendations is largely unknown. Our objective was to determine how much P may be removed by crops from subsurface soil layers and how the subsurface P level influences crop drawdown of P from the surface layer. Soil columns were prepared that contained all four possible combinations of low or high P levels in the surface soil and low or high P levels in the subsurface layer. The soil used was a Farnum fine sandy loam (fine‐loamy, mixed, thermic Pachic Argiustoll). Phosphorus removal was monitored by growing hybrid sorghum‐sudangrass [Sorghum bicolor(L.) Moench cv. ‘Honey Chow’] 84 days with an intermediate harvest after 35 days. Compared to when both the surface and subsurface layers had low P levels, P uptake increased when either or both layers had high P levels. Root growth and morphology responded to the P level of the soil layers. For all conditions, P uptake demonstrated a high correlation (R2=0.94) to an accessibility factor defined as the product of the available P level and root length summed for both soil layers. Comparing ratios of crop P removal to the change in soil test showed that P drawdown from the surface layer was reduced when the P‐supplying capacity of the subsurface layer was high. We concluded that available P in the subsurface layer can supply P to the crop, especially if the surface layer cannot supply sufficient P to meet crop demand. These results suggest that subsoil fertility should be considered in evaluating P available to crops and in estimating crop drawdown of available P.

This investigation was conducted to determine the concentration of 2,4,5‐T [(2,4,5‐trichlorophenoxy)acetic acid] and picloram (4‐amino‐3,5,6‐trichloropicolinic acid) in subsurface water after spray applications of the herbicides to the surface of a seepy area watershed and lysimeter in the Blacklands of Texas. A 1:1 mixture of the triethylamine salts of 2,4,5‐T + picloram was sprayed at 2.24 kg/ha every 6 months on the same area for a total of five applications. Herbicide content in the Houston Black clay during the study ranged from 0 to 162 ppb. Herbicide content on grass was high (28 to 113 ppm) immediately after spraying, but degraded rapidly after each treatment. Concentration of 2,4,5‐T and picloram in seepage and well water from the treated area was extremely low (<1 ppb) during the 3‐year study. No 2,4,5‐T was detected from 122 drainage samples from a field lysimeter sampled for 1 year after treatment with 1.12 kg/ha of 2,4,5‐T + picloram (1:1). Picloram was detected in small amounts (1 to 4 ppb) 2 to 9 months after treatment in lysimeter water.

Volatilization of NH3from NH4‐‐N salts applied to the surface of a calcareous soil was investigated. Ammonia losses from surface applied NH4F, (NH4)2SO4, and (NH4)2HPO4were 68, 54, and 51%, respectively, of the added NH4‐‐N in 100 hours. Ammonium nitrate, NH4Cl, and NH4I lost 18, 18, and 16%, respectively, of the added NH4‐N in 100 hours. An increase in pH at the soil surface resulted in higher loss of NH3. Applications of 550 kg N/ha as NH4F and (NH4)2SO4increased the pH from 7.6 to 8.9 and 8.1, although pH decreased rapidly with time. Soil pH decreased to 6.8 by the addition of 550 kg NH4‐N/ha as NH4NO3and changed very little in 50 hours. Ammonium sulfate applied to soils saturated with Mg2+and Ba2+gave similar results. Solubility of the apparent reaction product was the major factor regulating NH3volatilization. Formation of a Ca2+reaction product, such as CaSO4, tends to drive the reaction to the right and favors formation of (NH4)2CO3. A proposed mechanism of the observed loss of NH3is as follows: when an ammonium salt dissolves in a calcareous soil, (NH4)2CO3and a Ca2+salt of varying solubility forms. Ammonium carbonate subsequently decomposes, losing CO2at a faster rate than NH3. This causes formation of NH4OH and an increase in pH and greater NH3losses.

Relatively large, continuous soil pores were important pathways of downward Cl‐movement in saturated, swelling clay soils. Using water‐soluble fluorescein as a tracer for downward water and Cl‐movement in field basins, distinct small areas of the soil contained fluorescein, whereas nearby areas contained no visible fluorescein after Cl‐and fluorescein was ponded at the surface for 1.5 days. Chloride contents in the areas containing fluorescein were considerably higher than in nearby areas. Breakthrough curves of a large saturated core of undisturbed swelling clay soil indicated that Cl‐was moving quite rapidly through large connected pores. In the undisturbed swelling clay soil, the volume of soil water not containing Cl‐was about 60%; when the disturbed soil was repacked to the same density this value decreased to 40%. More of the original soil solution was eluted from long undisturbed cores than from short undisturbed cores of the same diameter before Cl‐appeared in the effluent. Apparently the longer core wall blocked more connected flow paths which were not vertical.

Hydraulic conductivities of Houston Black clay were measured in two field basins, in 73‐cm and 21‐cm diameter undisturbed cores, and in small cores prepared from sieved soil. Conductivities averaged about 2.5 cm/day for the field basins, about 0.3 cm/day for the undisturbed cores, and 0.1 cm/day for the disturbed soil cores. After steady‐state flow through the larger, undisturbed cores was obtained, water tagged with fluorescein was used to displace water in the cores until tagged water first appeared in the effluent. Examination of cross sections of the cores at different depths showed distinctive isolated areas where tagged water was present in the soil pores. The results imply that most water contained within structural units was inactive in the flow process compared to water flow around the units. The core walls apparently cut off some large pores associated with the soil structure, causing the decreased conductivities. Therefore, only field‐determined hydraulic conductivities are appropriate for use when predicting water flow in natural profiles of a swelling clay soil.

The redistribution of N, P, K, Ca, and Mg by corn from its vegetative parts to the developing ear was measured. This was accomplished by comparing a set of plants grown outdoors and harvested approximately 12 days after silking with a similar set of plants whose nutrient supply was cut off at the same time but which were allowed to grow to maturity. The increase in dry weight of ears between the first and second harvest was 174 g. The mean ear weight of the plants comprising the second harvest was 219 g. Chemical analysis of the various plant parts permitted a measure of the losses and gains of mineral elements from the first to second harvests. Of the total present in all vegetative plant parts at harvest 1, the following percentages of the various plant nutrients had moved out of the vegetative parts by harvest 2: N, 65%; P, 76%; K, 23%; Ca, 0%; Mg, 45%: If all the plant nutrients redistributed from the vegetative parts between harvest 1 and 2 moved to the developing ear, the following percentages of the nutrients in the mature ear were supplied by the redistribution process: N, 97%; P, 116%; K, 180%; Ca, 0%; and Mg 133%.

Biomasses such as peanut hulls or tree clippings have the potential for use in the production of chars, which can in turn be used as tools for environmental improvements. The purpose of this study was to evaluate the effectiveness of chars on reducing NH3 volatilization from poultry litter when used as a surface-applied treatment. The chars used were produced from 3 biomasses: peanut hulls, pine chips, and coconut husks. Peanut hull char (pH 9.2) was produced by pyrolyzing peanut hulls at 400°C for 30 min. The pine chip and coconut husk chars were acidified with sulfuric acid at a final concentration of 53% and had a pH of 2.0. Application rates were 0, 0.24, 0.37 + 0.37, and 0.73 kg/m2 to the floor of pens containing broilers at a commercial density (0.07 m2/bird). The addition of peanut hull char did not reduce NH3 concentrations in the air compared with untreated pine shavings bedding material. However, the use of acidified chars resulted in significant linear reductions in NH3 concentrations. The reduction in NH3 by the acidified chars was likely due to a combination of litter pH reduction and NH3 immobilization by the H2SO4 on the char. Bird performance was not adversely affected by any of the char treatments.