Ammonia volatilization from grassland receiving nitrogen fertilizer and rotationally grazed by dairy cattle

The micrometeorological mass balance method was used to measure ammonia (NH₃) volatilization from rotationally grazed swards throughout the 1987 and 1988 growing seasons. In both years the swards were dressed with calcium ammonium nitrate (CAN) split over 7 dressings. In 1987 the sward received a total of 550 kg N ha^–1, in 1988 a total of 550 or 250 kg N ha^–1. For the 550 kg N ha^–1 treatments there were 8 and 9 grazing cycles, respectively, in 1987 and 1988 and 7 for the 250 kg N ha^–1 treatment. Losses from the 550 N sward were 42.2 and 39.2 kg N ha^–1 in 1987 and 1988, respectively; this was equivalent to 8.5 and 7.7% of the N returned to the sward in the excreta of the grazing cattle. The NH₃ loss from the 250N sward was 8.1 kg N ha^–1 in 1988, which was equivalent to 3.1% of the N returned to the sward in excreta during the growing season. There was a wide variation in NH₃ volatilization between the individual grazing periods. This indicates the necessity of continued measurements throughout the growing season to obtain reliable data on NH₃ volatilization. Soil humidity is suggested to be a key factor, because emissions were high from wet soil, and low from drier soil. Results of a Monte Carlo simulation study showed that the measured NH₃ loss from the 250 and 550 N swards had a standard deviation of 13 and 5% of the mean, respectively.     

Nitrogen loss from different tillage systems and the effect on cereal grain yield

Grain yield, nitrogen (N) assimilation, ammonia (NH₃) volatilization, denitrification and fertilizer N distribution were examined in three commercially grown cereal crops; two were sown into conventionally tilled fields, while the third was direct drilled into an untilled field. The crops were top dressed with urea at establishment, tillering or ear initiation. Crop yield and N assimilation were measured in 16 m by 2.5 m plots receiving 0, 35, 70, 105, 140 or 175 kg N ha^–1. A mass balance micrometeorological technique was used to measure NH₃ volatilization, and other fertilizer N transformations and transfers were studied using¹⁵N labelled urea in microplots.On the conventionally tilled sites application of urea increased the grain yield of wheat from 3.9 to 5.5 t ha^–1, when averaged over the five application rates, three application times and two sites. There were no site or application time effects. However, on the direct drilled site, time of application had a significant effect on grain yield. When urea was applied at establishment, grain yield was not significantly increased and the mean yield (2.81 t ha^–1) was less than that obtained from treatments fertilized at tillering or ear initiation (4.09 and 4.0 t ha^–1, respectively). Much of the variation in grain yield at the no-till site could be ascribed to differences in NH₃ volatilization. At the no-till site, NH₃ losses were equivalent to 24, 12 and 1% of the N applied at establishment, tillering and ear initiation, respectively. Negligible volatilization of NH₃ occurred at the other sites. The surface soil at the no-till site had the highest urease activity and the soil was covered with alkaline ash resulting from stubble burning.Plant recovery of fertilizer N did not vary with application time on conventionally tilled sites (mean 62%). However, plant recovery of¹⁵N applied to the no-till site at establishment (35% of the applied N) was significantly less than that from plots where the application was delayed (45% at tillering and 55% at ear initiation, respectively). Leaching of N to below 300 mm depth was minimal (0 to 5% of the applied N). The calculated denitrification losses ranged from 1% to 14% of the applied N.The results show that the relative importance of NH₃ volatilization, leaching and denitrification varied with site and fertilization time. The importance of the various N loss mechanisms needs to be taken into account when N fertilization strategies are being developed.     

Transformations and losses of fertilizer nitrogen on no-till and conventional till soils

A field study was conducted in 1982 to measure the effect of no-till (NT) and conventional till (CT) systems on N transformation after surface and subsurface applications of N fertilizers. Urea, urea-ammonium nitrate (UAN) solution, (NH₄)₂SO₄ (AS), and CA(NO₃)₂ were applied to NT and CT plots (5.95 m²) at a rate of 448 kg N ha^–1. A comparison of fertilizer N recovered in soils receiving incorporated or surface applied N was used to estimate NH₃ volatilization while denitrification was estimated from fertilizer N recovered in the presence and absence of nitrapyrin with incorporated N. Immobilization was assessed in microplots (0.37 m²) after surface application of (¹⁵NH₄)₂SO₄ to NT and CT systems at a rate of 220 kg N ha^–1.The results indicate little difference between NT and CT systems on urea hydrolysis rates and immobilization of surface applied fertilizer N. Approximately 50% and 10% of the surface applied N was recovered in the inorganic and organic fractions, respectively, on both tillage systems. The N not recovered was likely lost from plot areas through soil runoff. Incorporation of UAN, urea and AS resulted in 20 to 40% greater inorganic N recovery than from surface application. Nitrification rates were greater under the NT than the CT system. The similarities in concentration in the various N pools observed between the two tillage systems may be partially due to the short length of time that NT was imposed in this field study (<1 year) since other researchers using established tillage systems (>5 y) indicate that NT tends to promote decreased efficiency of fertilizer N.     

Effect of urea granule size on ammonia volatilization from surface-applied urea

Urea powder and granules of varying size (1 to 8 mm diameter) were surface applied to a ryegrass/white clover pasture. Evolution of NH₃ was measured using a continuous air flow enclosure method. At 30 kg N ha^–1, the percentage of urea-N lost as NH₃ from powder or granules of 1–2, 3–4, 5.6 and 8 mm diameter was 18, 17, 20, 22 and 32 respectively. As the particle size increased, the rate of urea hydrolysis decreased and delayed the time at which the maximum rate of volatilization occurred. Mineral-N and soil surface pH measurements confirmed that during the period of volatilization, urea moved less than 30 mm from the application point.For the powder and 3–4 mm granule treatments, when the application rate was increased from 30 to 300 kg N ha^–1, the percentage of urea-N volatilized increased, but at any particular rate there was no significant difference in percentage loss between the powder and 3–4 mm granules.     

The fate of urea nitrogen applied in a foliar spray to wheat at heading

Nitrogen losses from irrigated wheat (cv. Matong) grown on a heavy clay in the Goulburn-Murray Irrigation Region following foliar applications of urea at heading were investigated. Ammonia (NH₃) volatilization was determined by a micrometeorological method and total nitrogen (N) loss was determined by a¹⁵N balance technique. The effects of the foliar application on grain N concentration and grain yield were determined also.Little nitrogen was lost by NH₃ volatilization following the foliar application. The rate of NH₃ loss increased briefly from <11 g N ha^–1 hr^–1 to >19 g N ha^–1 hr^–1 following rainfalls of 3 and 2 mm which washed 34% of the applied N from the plant onto the soil and increased the pH of the surface soil. The pH effect was short lived and total NH₃ loss amounted to only 2.13 kg N ha^–1 or 4.3% of the applied N.The¹⁵N balance study also showed that little N was lost from the plant-soil system until rain had washed the fertilizer from the plant onto the soil. In the period 152 to 206 DAS, the soil component of the applied N decreased from 34% to 9%. This fraction then increased slightly to 12% of the applied N at harvest. At that time, 69% of the applied N was recovered in the plants indicating that 19% of the applied N had been lost from the plant-soil system. As there was no evidence for leaching of N, the difference between total N loss as measured by¹⁵N balance (19%) and NH₃ loss (4%) is considered to be loss by denitrification (15%).The fertilizer N assimilated by the plant was efficiently remobilised from the leaves and stems to the head; 78% of the fertilizer N assimilated by the plant tops had been translocated to the head by the time of harvest. Grain N concentration responded to the foliar N application. The fitted response function had significant linear (P = 0.004) and quadratic (P = 0.10) trends to N rate, whereas there was no significant effect on grain yield.     

A comparison of methods of estimating ammonia volatilization in the field

Accurate estimation of the potential for NH₃ volatilization from urea-based fertilizers is an important step in attaining optimum N-use efficiency from these fertilizers. Published estimates of NH₃ volatilization losses from urea vary widely. Much of this variability may be due to the method of estimation and the degree of influence of the method on NH₃ loss. This study compared two field methods of estimating NH₃ volatilization in the field; a microplot-forced draft method, and a micrometeorogical method. Loss of NH₃ was estimated in three experiments following urea solution application to bare soil, and in two experiments following urea-ammonium nitrate solution application to wheat stubble residue. Both methods were found to be sensitive to soil and climatic variables influencing NH₃ volatilization. Cumulative N loss from the bare soil experiments ranged from 7 to 8 kg N ha^–1 for the microplot method and from 5 to 20 kg N ha^–1 for the micrometeorological method. Cumulative loss from wheat stubble residue ranged from 2 to 2.2 kg N ha^–1 for the microplot method and from 15 to 33 kg N ha^–1 for the micrometerological method. Loss of NH₃ was especially influenced by soil or residue water content and the influence of water content on the rate of urea hydrolysis. Maximum rates of loss were generally observed near midday, when water content at the soil surface was just beginning to decline and the surface temperature was rapidly rising. The microplot method was found to have a greater potential for affecting the environment and thus influencing NH₃ loss measurements than the micrometeorological method. Windspeed and mixing at the soil surface was influenced by the presence of the microplot cylinder and lid, especially in the wheat residue experiments. It is likely that the micrometeorological method, with its minimal influence on the field environment, more accurately reflects actual levels of ammonia loss. The primary advantage of the microplotforced draft method is its ability to easily compare relative NH₃ losses from different treatments.Contribution No. 87-300-J from the Kansas Agricultural Experiment Station. Part of a dissertation submitted by the senior author in partial fulfillment of the requirements for the Ph. D. Degree at Kansas State University. The research was supported in part by grants from Farmland Industries, Inc., and USDA-ARS.     

Fruit yield of Valencia sweet orange fertilized with different N sources and the loss of applied N

Nutrient management recommendations are needed to increase nitrogen uptake efficiency, minimize nutrient losses and reduce adverse effects on the environment. A study of the effects of nitrogen fertilization on N losses and fruit yield of 6-yr-old Valencia sweet orange (Citrus sinensis (L.) Osb.) on Rangpur lime rootstock (C. limonia Osb.) grove was conducted in an Alfisol in Brazil from 1996 to 2001. Urea (UR) or ammonium nitrate (AN) fertilizers were surface-applied annually at rates of 20, 100, 180, and 260 kg N ha^–1 split into three applications from mid-spring to early fall. A semi-open trapping system, using H₃PO₄ + glycerol-soaked plastic foams, was used for selected treatments in the field to evaluate NH₃ volatilized from applied N fertilizers. Ammonia volatilization reached 26 to 44% of the N applied as UR at the highest rate of N used. Ammonia volatilization losses with AN were lower (4% of the N applied). On the other hand, AN resulted in greater nitrate leaching and greater soil acidification than UR. A marked effect of AN fertilizer on soil pH (CaCl₂) in the 0–20 cm depth layer was observed with a decrease of up to 1.7 pH units at the highest N rate. Acidification was followed by a decrease in exchangeable Ca and Mg; consequently, after 5 yr of fertilization with AN, soil base saturation dropped from 77% in the plots treated with 20 kg N ha^–1 per year, to 24% in those that received 260 kg N ha^–1 per year. The effect of N sources on fruit yield varied from year to year. In 2001, for a calculated N application rate of 150 kg ha^–1, the fertilizer efficiency index of UR was 75% of that of AN.     

Effects of soil fumigation and N source on soil inorganic N and tomato growth

Soil fumigation, commonly used in vegetable production, may alter the rate of nitrification, affecting availability of N for crop use. The objective of this research was to examine effects of soil fumigation and N fertilizer source on tomato growth and soil NO₃–N and NH₄–N in field production. Experiments 1 and 2 included application of methyl bromide at 420 kg ha^-1 to a Norfolk sandy loam (fine loamy siliceous thermic Typic Kandiudult) in combination with preplant applications of calcium nitrate, ammonium nitrate, and ammonium sulfate at 144 kg N ha^-1. An additional fumigant, metam-sodium, was included in the second experiment at 703 L ha^-1 (268 kg sodium methyldithiocarbamate ha^-1). Experiment 3 included methyl bromide and metam-sodium, with ammonium sulfate as the sole source of N applied at 144 kg N ha^-1. In the first two studies, fumigants had little or no effect on soil NH₄–N or NO₃–N concentration. Tomato plants were larger and fruit yield was greater in fumigated plots, but there were few growth or yield responses to N source. In the third experiment, fumigants increased concentration of soil NO₃–N and NH₄–N at 16 days after fumigation (DAF), however, there was no effect on nitrification owing to fumigants. It appears that N source selection to overcome inhibition of nitrification is not necessary in plant production systems that involve fumigation     

Ammonia volatilization from fertilizers applied to irrigated wheat soils

A series of experiments using flow chambers was undertaken in the field to investigate the effects of stubble and fertilizer management, soil moisture and precipitation on ammonia volatilization following nitrogen application on chromic luvisols. In the first factorial experiment, urea at 100 kg N ha^–1 was applied to the soil surface one, three and six days following irrigation; there were four rice stubble management systems comprising stubble burnt, stubble burnt then rotary hoed, stubble rotary hoed into the soil and stubble retained on the surface. Cultivation almost halved ammonia loss. The higher loss from uncultivated plots was ascribed to an alkaline ash bed on burnt plots, and to higher soil moisture and some retention of urea prills in the crop residue above the soil surface of the stubble retention plots. Average volatilization over a 12 day period following urea application from plots fertilizer one, three or six days after irrigation was 16, 15 and 4 kg N ha^–1, respectively. Daily application of up to 1.7 mm of water did not reduce volatilization and 35 kg N ha^–1 was lost within five days of fertilization. Daily precipitation of 6.8 mm reduced loss to 14 kg N ha^–1. This quantity of rain is uncommon in the region and it was concluded that showery conditions are unlikely to reduce volatilization. The third experiment demonstrated that the quantity of stubble on the soil surface had no effect on volatilization, and all plots lost 25% of applied nitrogen. In the fourth experiment, 100 kg N ha^–1 as urea or ammonium nitrate was either broadcast onto the surface or stubble retention plots, or placed, and partly covered to simulate topdressing with a disc implement. Partial burial of urea reduced ammonia volatilization from 36 to 7 kg N ha^–1, while partial burial of ammonium nitrate reduced loss from 4 to 0 kg N ha^–1.     

Ammonia volatilization from drill sown rice bays

Ammonia volatilization losses and other N transformations were studied in drill sown rice bays fertilized with urea at various times between permanent flooding (PF) and panicle initiation (PI). Ammonia loss was measured directly with flow chambers and indirectly through application of Freney et al.'s (1985) model. Both techniques indicated that ammonia volatilization was negligible from fields fertilized immediately before PF. Applying 100 kg urea-N ha^–1 to floodwater one day after flooding significantly increased floodwater ammoniacal-N and urea-N content, however the concentrations fell rapidly over the following five days. Fertilizer-N dissolved in the floodwater was in the urea rather than the ammoniacal-N form, indicating slow hydrolysis until it moved into the soil. Floodwater on plots receiving urea one day after PF frequently had more than double the NO₃-N concentration of plots fertilized before flooding.Applying up to 140 kg urea-N ha^–1 at PI increased floodwater ammoniacal-N concentrations from almost zero to over 27 g m^–3, but three days after fertilization there was less than 3 g m^–3 present. Fertilization also increased NH₄-N concentration in the top 40 mm of soil. Higher ammoniacal-N concentration at PI suggests higher urease activity. Floodwater pH at PI was low, with a mean daily maximum of 7.8 and this reduced ammonia loss to less than 1% of the applied N.The results indicate that volatilization from fields fertilized prior to PF is minimal because of the low floodwater pH and ammoniacal-N concentration, while low floodwater pH restricts volatilization from fields topdressed at PI.     

An assessment of N loss from agricultural fields to the environment in China

Using the 1997 IPCC Guidelines for National Greenhouse Gas Inventory Methodology, and statistical data from the China Agricultural Yearbook, we estimated that the direct N₂O emission from agricultural fields in China in 1990 was 0.282 Tg N. Based on micro-meteorological field measurement of NH₃ volatilization from agricultural fields in different regions and under different cropping systems, the total NH₃ volatilization from agricultural fields in China in 1990 was calculated to be 1.80 Tg N, which accounted for 11% of the applied synthetic fertilizer N. Ammonia volatilization from agricultural soil was related to the cropping system and the form of N fertilizer. Ammonia volatilization from paddy fields was higher than that from uplands, and NH₄HCO₃ had a higher potential of NH₃ volatilization than urea. N loss through leaching from uplands in north China accounted for 0.5–4.2% of the applied synthetic fertilizer N. In south China, the leaching of applied N and soil N from paddy fields ranged from 6.75 to 27.0 kg N ha^-1 yr^-1, while N runoff was between 2.45 and 19.0 kg N ha^-1 yr^-1.     

Influence of long-term changes in nitrogen flows on the environment: A case study of a city in Hokkaido, Japan

There is an urgent need to establish sustainable nutrient cycling. Changes in amounts of N flow and separation of production and consumption sectors are becoming a serious environmental problem. In this study, the yearly N in- and outflow of a city in northern Japan from 1912 to 2002 was investigated based on the statistics and inventory data. Based on the characteristics of the N flow, the period was divided into manure-based period (MBP, 1912–1950), transition period from manure- to chemical fertilizer-based period (TP, 1950–1970), and chemical fertilizer-based period (CBP, 1970–2002). The highest amount of N inflow (up to 350 Mg N y^–1) was observed at the end of the MBP, and the second peak (about 300 Mg N y^–1) at the beginning of the CBP. The N application rate on farmland increased from 68 kg N ha^–1 in 1912 to above 250 kg N ha^–1 in the 1950s, then decreased to 168 kg N ha^–1 in 2002. The farmland productivity increased from 30 kg N ha^–1 at the end of the 1950s to 90 kg N ha^–1 in 2002, due to improvement in crop varieties and management methods. In MBP surplus N in farmland and NH₃ volatilization accounted for 90% of the N outflow from the city, then in CBP, disposal N and surplus N in farmland became the main N outflow. All these outputs are considered to increase the N concentration in rivers and/or underground water. In the case of surplus N in farmland, it exceeded the amount of optimum N management (<50 kg N ha^–1; , Agricult. Ecosyst. Environ. 72: 35–52) during 1935–1970 and 1981–1997. In order to prevent degradation of the environment through artificially altered nutrient flow, we need to be aware of the environmental impact of the N flow and establish proper N management practices.     

Residual fertilizer nitrogen as influenced by timing and nitrogen forms in a silty clay soil under sugarcane in Mauritius

A field study was initiated to investigate the influence of application time on the disposition of 100 kg N ha^–1 applied as¹⁵N-labelled NaNO₃ and (NH₄)₂SO₄ to a silty clay soil (a ustic eutropept) under sugarcane (Saccharum hybrid sp.) in Mauritius. The results showed that the vertical and lateral distribution of residual fertilizer N remaining in the soil 2 years after fertilization was not influenced by the chemical nature of N used nor by the time of application. On account of rapid biological immobilization more than 50% of the residual N in the soil remained in the surface 15-cm layer and less than 30% of fertilizer N had moved laterally more than 30 cm away from the zone of fertilization. There was however more residual fertilizer N in the soil when the N was applied in September (23 kg N ha^–1) than in December (16 kg N ha^–1) because fertilizer N applied during the active sugarcane growth in December was used more efficiently than similar applications in September when growth was slow. The present study provides further evidence to substantiate that N leaching is not of significant concern in soils located in a tropical environment similar to that of Mauritius.     

The effect of fertiliser type and application rate on denitrification losses from cut grassland in Northern Ireland

Denitrification losses were measured using the acetylene inhibition technique adapted for a coring procedure. Two soils under a cut ryegrass sward were used. One soil was a freely-drained clay loam receiving under 900 mm rainfall annually, the other soil being a poorly-drained silty clay receiving over 1100 mm rainfall annually. Swards at each site received up to 300 kg N ha^–1 yr^–1 of calcium ammonium nitrate (CAN), urea or a new fertiliser mixture GRANUMS (30% ammonium nitrate, 30% urea, 10% ammonium sulphate, 30% dolomite). For both soils the rate of denitrification exceeded 0.1 kg N ha^–1 day^–1 only when the air-filled porosity of the soil was < 30% v/v and soil nitrate was > 2 mg N kg^–1 in the top 10cm of the profile and when soil temperature at 10 cm was > 4°C. When the soils dried such that their air-filled porosity was > 30% v/v, denitrification rates decreased to < 0.08 kg N ha^–1 day^–1. Highest rates (up to 3.7 kg N ha^–1 day^–1) were observed on the clay soil following application of 94 kg N ha^–1 CAN to soil near field capacity in early summer 1986. Losses from CAN were approximately 3 times those from urea for a given application. Denitrification losses from the GRANUMS treatment were, overall, intermediate between those from CAN and urea but the daily losses more closely resembled those from the CAN treatment. The impeded drainage on the clay soil, where soil moisture contents remained close to field capacity throughout the year, showed denitrification losses roughly 3 times those observed on the more freely drained clay-loam for any given treatment. Over a 12-month period, N losses arising from denitrification were 29.0 and 10.0 kg N ha^–1 for plots receiving 300 kg N ha^–1 CAN and urea, respectively, on the well drained clay-loam and 79.0 and 31.1 kg N ha^–1 respectively, for identical plots on the poorly drained clay soil. Annual denitrification losses from control plots were < 1 kg N ha^–1 on both soils.     

The combined effect of fertiliser nitrogen and phosphorus on herbage yield and changes in soil nutrients of a grass/clover and grass-only sward

The combined effect of reduced nitrogen (N) and phosphorus (P) application on the production of grass-only and grass/clover swards was studied in a five-year cutting experiment on a marine clay soil, established on newly sown swards. Furthermore, changes in soil N, P and carbon (C) were measured. Treatments included four P (0, 35, 70 and 105 kg P ha^–1 year^–1) and three N levels (0, 190 and 380 N kg ha^–1 year^–1) and two sward types (grass-only and grass/clover). Nitrogen was the main factor determining the yield and quality of the harvested herbage. On the grass-only swards, N application increased the DM yield with 28 or 22 kg DM kg N^–1, at 190 or 380 kg N ha^–1 year^–1, respectively. The average apparent N recovery was 0.78 kg kg^–1. On the grass/clover swards, N application of 190 ha^–1 year^–1 increased grass production at the cost of white clover, which decreased from 41 to 16%. Phosphorus application increased grass yields, but did not increase clover yields. A positive interaction between N and P applications was observed. However, the consequences of this interaction for the optimal N application were only minor, and of little practical relevance. Both the P-AL-value and total soil P showed a positive response to P application and a negative response to N application. Furthermore, the positive effect of P application decreased with increasing N application. The annual changes in P-AL-value and total soil P were closely related to the soil surface surplus, which in turn was determined by the level of N and P application and their interaction. The accumulation of soil N was similar on both sward types, but within the grass-only swards soil N was positively affected by N application. The accumulation of organic C was unaffected by N or P application, but was lower under grass/clover than under grass-only.     

Response of dryland wheat to fertilizer nitrogen in relation to stored water,rainfall and residual farm yard manure

Yield response of dryland wheat to fertilizer N application in relation to components of seasonal water (available soil moisture and rainfall) and residual farm yard manure (FYM) was studied for five years (1983–84 to 1987–88) on a maize-wheat sequence on sandy loam soils in Hoshiarpur district of Punjab, India. Four rates of N viz. 0, 40, 60 and 80 kg ha^–1 in wheat were superimposed on two residual FYM treatments viz. no FYM (F₀) and 15 t ha^–1 (F₁₅) to preceding maize. FYM application to maize increased the residual NO₃-N content by 19–30 kg ha^–1 in the 180 cm soil profile. For a given moisture distribution, F₁₅ increased attainable yields. Over the years, F₁₅ increased wheat yield by 230 to 520 kg ha^–1. Response to fertilizer N was lower in FYM amended plots than in unamended plots. Available soil moisture at wheat seeding and amount and distribution of rainfall during the vegetative and the reproductive phases of crop development affected N use efficiency by wheat. Available soil moisture at seeding alone accounted for 50% variation in yield. The residual effect of FYM on wheat yield could be accounted for by considering NO₃-N in 180 cm soil profile at seeding. The NO₃-N and available soil moisture at wheat seeding along with split rainfall for two main phases of crop development and fertilizer N accounted for 96% variation in wheat yield across years and FYM treatments.     

The effect of grazing intensity and the presence of a forage legume on nitrogen dynamics in Brachiaria pastures in the Atlantic forest region of the south of Bahia, Brazil

It has been shown that with careful grazing management and addition of Pand K, but not N, fertilisers Brachiaria pastures are ableto maintain sustainable live weight gains over many years. However, standardon-farm practice, which generally involves high stocking rates, leads after afew years to pasture decline due mainly to N deficiency for grass regrowth. Togenerate an understanding of the mechanism of pasture decline and possiblemanagement options to mitigate this process, a study was performed in theAtlantic forest region of the south of Bahia state to study the N dynamics inpastures of Brachiaria humidicola subject to threedifferent stocking rates of beef cattle, with and without the presence of theforage legume Desmodium ovalifolium. Despite the fact thatthe C:N ratio of the deposited litter was high (60 to 70) the rate ofdecomposition was very rapid (k –0.07 gg^–1 day^–1) and annual rates of Nturnover through the litter pathway were between 105 and 170 kg Nha^–1 year^–1. In the grass-onlypasturesas stocking rate increased from 2 to 3 head ha^–1, N recycledinthe litter decreased by 11%, but a further increase to 4 headha^–1 decreased N recycling by 30% suggesting thatbeyonda certain critical level higher grazing stocking rates would lead to pasturedecline if there was no N addition. High stocking rates decreased theproportionof the legume in the sward, but at all rates the concentration of N in both thegreen and dead grass in the forage on offer and in the litter was higher in themixed sward. The presence of the legume caused a decrease in the C:N ratio ofthe microbial biomass while both soil N mineralisation and nitrificationincreased. This increased rate of turnover of the microbial biomass and thecontribution of N₂ fixation to the legume resulted in largeincreasesin the N recycled via litter deposition ranging from 42 to 155 kg Nha^–1 year^–1.     

Effects of improved drainage and nitrogen source on yields, nutrient uptake and utilization efficiencies by maize (Zea mays L.) on Vertisols in sub-humid environments

Nitrogen is the most limiting plant nutrient in Vertisols in Kenya. Soil properties, climatic conditions and management factors as well as fertilizer characteristics can influence fertilizer nitrogen (N) use efficiency by crops. Vertisols, characterized by low-basic water infiltration rate, are prone to waterlogging under sub-humid and humid conditions. We determined effects of drainage, N source and time of application on yields, nutrient uptake and utilization efficiencies by maize grown on Vertisols in sub-humid environments. Treatments comprised two furrows (40 cm and 60 cm deep) and a check (i.e., no furrow), calcium nitrate to furnish NO₃-N, ammonium sulphate to supply NH₄-N at 100 kg N ha⁻¹, a control (i.e., no fertilizer N), and fertilizer N application at sowing, 40 days after sowing, and split (i.e., half the rate at sowing and half 40 days after sowing). A split-plot design was used in which drainage formed the main plots and N source × time of N application formed the sub-plots. Higher grain and total dry matter yields, harvest index, leaf N content, uptake of N, P and K, as well as N agronomic (NAE) and recovery (NRE) efficiencies were obtained from drained compared to undrained plots. The increase ingrain yields as a result of drainage varied from 31 to 45% for control, 35 to 43% for NO₃-N, and 16 to 21% for NH₄-N treatments. Drainage resulted in total N uptake increases from 50 to 80 kg N ha⁻¹ in control plots, 80 to 130 kg N ha⁻¹ in NO₃-N treated plots, and 90 to 130kg N ha⁻¹ in NH₄-N treated plots. Ammonium-N source was superior to NO₃-N source in terms of higher yields, NAE, and NRE in undrained plots, but the two N sources behaved similarly in drained plots. Delayed or split NO₃-N application gave higher yields, NAE and NRE than when all N was applied at sowing in undrained plots. There was no difference between 40 cm and 60 cm deep furrows in terms of crop yields and nutrient use efficiencies. Thus, draining excess water with furrows at least 40 cm deep is essential for successful crop production in these Vertisols under sub-humid conditions. This revised version was published online in November 2006 with corrections to the Cover Date.     

Effect of poultry litter and composts on soil nitrogen and phosphorus availability and corn production

Environmental problems associated with raw manure application might bemitigated by chemically or biologically immobilizing and stabilizing solublephosphorus (P) forms. Composting poultry litter has been suggested as a means tostabilize soluble P biologically. The objectives of this study were to assessthe nutrient (N, P) value of different-age poultry litter (PL) compostsrelativeto raw poultry litter and commercial fertilizer and determine effects ofpoultrylitter and composts on corn (Zea mays) grain yield andnutrient uptake. The research was conducted for two years on Maryland'sEastern Shore. Six soil fertility treatments were applied annually to aMatapeake silt loam soil (Typic Hapludult): (1) a check without fertilizer, (2)NH₄NO₃ fertilizer control (168 kg Nha^–1), (3) raw poultry litter (8.9 Mgha^–1), (4) 15-month old poultry litter compost (68.7Mg ha^–1), (5) 4-month old poultry litter compost(59 Mg ha^–1) and (6) 1-month old poultry littercompost (64 Mg ha^–1). We monitored changes inavailable soil NO₃-N and P over the growing season and post harvest.We measured total aboveground biomass at tasseling and harvest and corn yield.We determined corn N and P uptake at tasseling.Patterns of available soil NO₃-N were similar between raw PL-and NH₄NO₃ fertilizer-amended soils. LittleNO₃-N was released from any of the PL composts in the first year ofstudy. The mature 15-month old compost mineralized significant NO₃-Nonly after the second year of application. In contrast, available soil P washighest in plots amended with 15-month old compost, followed by raw PL-amendedplots. Immature composts immobilized soil P in the first year of study. Cornbiomass and yields were 30% higher in fertilizer and raw PL amendedplotscompared to yields in compost-amended treatments. Yields in compost-amendedplots were greater than those in the no-amendment control plots. Corn N and Puptake mirrored patterns of available soil NO₃-N and P. Corn Puptakewas highest in plots amended with 15-month old compost and raw PL, even thoughother composts contained 1.5–2 times more total P than raw PL. There wasalinear relationship between amount of P added and available soil P, regardlessof source. The similar P availabilities from either raw or composted PL,coupledwith limited crop P uptake at high soil P concentrations, suggest that raw andcomposted PL should be applied to soils based on crop P requirements to avoidbuild-up of available soil P.     

Reducing N losses (NH3, N2o, N2) and immobilization from slurry through optimized application techniques

In model, pot and field trials the effect of C reduced slurries and different application techniques on N losses and N immobilization were investigated. The C reduced slurries were produced by mechanical separation. Ammonia losses from surface-applied and injected cattle slurry were measured under field conditions using a wind tunnel system. Injection of slurry was the most efficient way to reduce volatilization of ammonia. After 6 days the total loss from the injected slurry was only 9% of that from surface band application. Furthermore, additional losses of N may occur through denitrification, specially after injection of slurry which may create an anaerobic environment abundant in readily oxidizable C. Therefore denitrification measurements by the acetylene inhibition technique were conducted. Until 100 days after application the loss from the injected slurry was 7.3 kg compared to 4.5 kg N ha^–1 from surface band applied slurry. After injection, denitrification was only 4.1 kg N ha^–1 for C reduced compared to 6.5 kg N ha^–1 for normal slurry. In pot trials the ammonium-¹⁵N of normal slurry and C-reduced slurry was utilized by oats between 52 and 60%, the ammonium sulfate by 67%. The increased biomass C confirmed a greater immobilization of the NH₄-N of the normal slurry resulting in a lower initial efficiency.Dedicated to Prof. Dr. A. Amberger on his 75th birthday