Initial and residual effects of nitrogen fertilizers on grain yield of a maize/bean intercrop grown on a Humic Nitosol and the fate and efficiency of the applied nitrogen

Initial and residual effects of nitrogen (N) fertilizers on grain yield of a maize/bean intercrop grown on a deep, well-drained Humic Nitosol (66% clay, 3% organic carbon) were evaluated. Enriched (¹⁵N) N fertilizer was used to study the fate of applied N in two seasons: using urea (banded) at 50 kg N ha^–1 in one season, and¹⁵N-enriched urea (banded), calcium ammonium nitrate (CAN, banded), and urea supergranules (USG, point placement) were applied in the other season (different field) at 100 kg N ha^–1. Nitrogen fertilizer significantly (P = 0.05) increased equivalent maize grain yield in each season of application with no significant differences between N sources, i.e., urea, CAN, and USG. Profitmaximizing rates ranged from 75 to 97 kg N ha^–1 and value: cost ratios ranged from 3.0 to 4.8. Urea gave the highest value: cost ratio in each season. Most (lowest measurement 81%) of the applied N was accounted for by analyzing the soil (to 150 cm depth) and plant material. Measurements for urea, CAN, and USG were not significantly different. The high N measurements suggest low losses of applied N fertilizer under the conditions of the study. Maize plant recovery ranged from 35 to 55%; most of this N (51–65%) was in the grain. Bean plant recovery ranged from 8 to 20%. About 34–43% of the applied N fertilizer remained in the soil, and most of it (about 70%) was within the top soil layer (0–30 cm). However, there were no significant equivalent maize grain increases in seasons following N application indicating no beneficial residual effect of the applied fertilizers.     

Fertilizer requirement of rice-wheat and maize-wheat rotations on coarse-textured soils amended with farmyard manure

Field experiments with rice-wheat rotation were conducted during five consecutive years on a coarse-textured low organic matter soil. By amending the soil with 12t FYM ha^–1, the yield of wetland rice in the absence of fertilizers was increased by 32 per cent. Application of 80 kg N ha^–1 as urea could increase the grain yield of rice equivalent to 120 kg N ha^–1 on the unamended soil. Although the soil under test was low in Olsen's P, rice did not respond to the application of phosphorus on both amended and unamended soils. For producing equivalent grain yield, fertilizer requirement of maize grown on soils amended with 6 and 12 t FYM ha^–1 could be reduced, respectively to 50 and 25 per cent of the dose recommended for unamended soil (120 kg N + 26.2 kg P + 25 kg K ha^–1). Grain yield of wheat grown after rice on soils amended with FYM was significantly higher than that obtained on unamended soil. In contrast, grain yield of wheat which followed maize did not differ significantly on amended or unamended soils.     

Very high applications of nitrogen fertilizer on grassland and residual effects in the following season

At very high nitrogen applications (480 and more kg N ha^–1 yr^–1) in field trials on all-grass swards the amount of N applied exceeded the amount of N harvested. In the humid temperate climate of the Netherlands in the subsequent spring approximately 25, 40, and 50% of this excess nitrogen was recovered as accumulated mineral nitrogen in the 0–100 cm layer of sandy, clay and heavy clay soil, respectively. The effect of this excess nitrogen on growth during the subsequent season was measured through the increase in DM and N yield over a reference treatment. In this season all treatments received a uniform application (40 kg N ha^–1 cut^–1). Residual effects were absent on sandy soil but distinct on the clay soils. On the clay soils each accumulated kg soil mineral nitrogen produced 15 kg DM. Assuming a relatively small contribution of residual nitrogen carried over in stubble, roots and organic matter, the accumulated soil mineral nitrogen would seem to be as effective as applied fertilizer nitrogen.     

Long-term effect of N and P fertilization on a pearlmillet—wheat cropping system

Results of an eight-year study on long-term effect of N and P application in a pearlmillet—wheat sequence is reported. There was little or no residual effect of N on any of the crops. Pearlmillet needed 70 to 80 kg N and wheat required more than 120 kg N ha^–1 every year for optimum grain yield. There was no soluble P build up in soil by continuous P application. Fertilizing wheat every year with 19 kg P and pearlmillet with 13 kg P ha^–1 is considered optimum.Continuous cropping leading to a production of 216 tonnes of biomass ha^–1 in 17 crops and use of high analysis N (urea) and P (triple superphosphate) fertilizers had not impaired the K and Zn supplying capacity of these alluvial soils containing illite clay minerals. The experiment is being continued to monitor the productivity of the soil as affected by continuous cropping.     

Effects of type and amount of applied nitrogen fertilizer on nitrous oxide fluxes from intensively managed grassland

Five field experiments and one greenhouse experiment were carried out to assess the effects of nitrogen (N) fertilizer type and the amount of applied N fertilizer on nitrous oxide (N₂O) emission from grassland. During cold and dry conditions in early spring, emission of N₂O from both ammonium (NH ₄ ⁺ ) and nitrate (NO ₃ ^– ) containing fertilizers applied to a clay soil were relatively small, i.e. less than 0.1% of the N applied. Emission of N₂O and total denitrification losses from NO ₃ ^– containing fertilizers were large after application to a poorly drained sand soil during a wet spring. A total of 5–12% and 8–14% of the applied N was lost as N₂O and via denitrification, respectively. Emissions of N₂O and total denitrification losses from NH ₄ ⁺ fertilizers and cattle slurry were less than 2% of the N applied. Addition of the nitrification inhibitor dicyandiamide (DCD) reduced N₂O fluxes from ammonium sulphate (AS). However, the effect of DCD to reduce total N₂O emission from AS was much smaller than the effect of using NH ₄ ⁺ fertilizer instead of NO ₃ ^– fertilizer, during wet conditions. The greenhouse study showed that a high groundwater level favors production of N₂O from NO ₃ ^– fertilizers but not from NH ₄ ⁺ fertilizers. Inereasing calcium ammonium nitrate (CAN) application increased the emitted N₂O on grassland from 0.6% of the fertilizer application rate for a dressing of 50 kg N ha^–1 to 3.1% for a dressing of 300 kg N ha^–1. In another experiment, N₂O emission increased proportionally with increasing N rate. The results indicate that there is scope for reducing N₂O emission from grasslands by choosing the N fertilizer type depending on the soil moisture status. Avoiding excessive N application rates may also minimize N₂O emission from intensively managed grasslands.     

Effect of urea management on yield and N use efficiency of lowland rice on an acid sulfate soil

Field experiments were conducted during 1988–1989 at two adjacent sites on an acid sulfate soil (Sulfic Tropaquept) in Thailand to determine the influence of urea fertilization practices on lowland rice yield and N use efficiency. Almost all the unhydrolyzed urea completely disappeared from the floodwater within 8 to 10 d following urea application. A maximum partial pressure of ammonia (pNH₃) value of 0.14 Pa and an elevation in floodwater pH to about 7.5 following urea application suggest that appreciable loss of NH₃ could occur from this soil if wind speeds were favorable. Grain yields and N uptake were significantly increased with applied N over the control and affected by urea fertilization practices (4.7–5.7 Mg ha^–1 in dry season and 3.0–4.1 Mg ha^–1 in wet season). In terms of both grain yield and N uptake, incorporation treatments of urea as well as urea broadcasting onto drained soil followed by flooding 2 d later were more effective than the treatments in which the same fertilizer was broadcast directly into the floodwater either shortly or 10 d after transplanting (DT). The¹⁵N balance studies conducted in the wet season showed that N losses could be reduced to 31% of applied N by broadcasting of urea onto drained soil and flooding 2 d later compared with 52% loss by broadcasting of urea into floodwater at 10 DT. Gaseous N loss via NH₃ volatilization was probably responsible for the poor efficiency of broadcast urea in this study.     

Ammonia losses from ammonium-containing and -forming fertilizers after surface application at different rates on alkaline soils

The objective of this investigation was to compare the susceptibility of different ammonium containing and forming fertilizers to NH₃ losses and to determine the effect of application rates on NH₃ volatilization. Losses of NH₃ from five fertilizers, namely (NH₄)₂SO₄, CAN, urea, MAP and DAP were determined. The fertilizers were surface-applied to a sandy clay loam Arniston soil and a clayey Gelykvlakte soil of which the pH values were respectively 9.0 and 8.9. The application levels were equivalent to 0, 15, 30, 60, 120 and 240 kg N ha^–1. After a contact period of 3 days NH₃ losses were determined. Ammonia was lost from both soils under all treatments. More NH₃ was lost from the clayey Gelykvlakte soil compared with the sandy clay loam Arniston soil. Loss of NH₃ from the various fertilizers was ranked as follows: Urea > DAP > (NH₄)₂SO₄ > MAP > CAN. Ammonia losses increased with increasing application rates, but the proportion of N lost, decreased. Losses of NH₃ may be reduced by selective choice of fertilizer type and application rate.     

Evaluation and model of temperature and rainfall effects on response to N sources applied to grassland in spring

Direct and residual effects of urea and calcium ammonium nitrate (CAN) on dry matter (DM) response were measured at a total of 12 application times in early spring over three years. The variation in the direct effect was described by models that included temperature and long-term rainfall for CAN and, additionally, short-term rainfall for urea. The operative temperature was the accumulated mean daily air temperature for combined intervals pre-application and postapplication of N. The effect of rainfall was apparent only when the data were adjusted for temperature.Simulation studies with the models indicated that, although the influence of temperature was dominant, rainfall modified it strongly in terms of the relative efficiencies of the two N sources and the magnitude of response. For instance, the temperature-induced increase in DM response to urea between cold and normal years was 402 kg ha^–1 for a specified period, whereas differences between dry and wet years were decreases of 166 and 259 kg ha^–1 in the case of urea and CAN, respectively. Short-term rainfall had a positive effect on response to urea.The experimental values varied widely both between and within years. The direct effect of the application of urea at 50 kg N ha^–1 varied from 0 to 750 kg DM ha^–1, and the residual effect varied from 0 to 1620 kg DM ha^–1. The corresponding values for apparent N recovery varied from 0.1 to 45% and from 7 to 68%, respectively. The efficiency of urea was comparable to, and in instances better than, CAN.     

Effects of urea fertigation of apple trees on soil pH,exchangeable cations and extractable manganese in a sandy loam soil in New Zealand

Changes in soil pH, exchangeable aluminium (Al), calcium (Ca), magnesium (Mg), and potassium (K) and extractable manganese (Mn) were investigated after urea fertigation of a sandy loam soil in an apple orchard in New Zealand. Urea at three rates (0, 25, 50 kg N ha^–1 yr^–1 or 0, 16.9, 33.8 g N emitter^–1 yr^–1) was applied in 4 equal fertigations. Soil cores at 4 profile depths (0–10, 10–20, 20–40 and 40–60 cm) directly below and 20 cm from the emitter were sampled approximately 4 weeks after each fertigation and in the following winter. Results obtained showed that the largest changes in soil pH and cations occurred in soils directly below the emitter in the 50 kg N ha^–1 yr^–1 treatment where the soil pH decreased by 1.6 pH units at all soil depths. The lowest pH of 4.3 was observed at a depth of 27 cm. Exchangeable Al and extractable Mn levels increased to 11 meq kg^–1 and 78µg g^–1 respectively. Estimated losses of Ca, Mg and K from the upper soil profile depth (0–10 cm) represented 23, 63 and 27% of their respective total exchangeable levels. At lower profile depths (>20 cm), accumulation of displaced K was evident. Variable, and generally non-significant, chemical changes recorded in soils 20 cm from the emitter were attributed to restricted lateral water movement, and therefore urea movement, down the profile.The present study showed that one season of urea fertigation by trickle emitters, applied to a sandy loam, at half the rate conventionally applied to apple orchards (50 kg N ha^–1 yr^–1) resulted in pH and mineral element imbalances which were potentially and sufficiently severe to inhibit tree growth.     

N application to winter wheat at tillering and shooting: N balance at different growth stages

At two sites, microplots under winter wheat were given 140 kg N ha^–1 as labelled ammonium nitrate split in 80 kg N ha^–1 at tillering and 60 kg N ha^–1 at shooting. Soil and plant samples were analyzed at shooting, after anthesis and at grain harvest and a¹⁵N balance was established. The average recovery rate of 95% indicates that there were no marked N losses due to leaching and denitrification, which is attributed to the low rainfall in the two months after fertilizer application. Between 19 and 23% of the fertilizer N remained in the 0–30 cm soil layer as organically bound soil N. Up to 64% was taken up by the above-ground crop. On the loamy sand, 4% of the fertilizer N at harvest remained in the roots in the 0–30 cm layer and only 3% was found as inorganic N in the 0–90 cm soil layer. The fertilizer N applied diminished plant uptake of soil N in the period between fertilizer application and harvest. As compared with the control, the fertilized plants extracted 25 and 28% less soil N from loamy sand and loess soil, respectively. The results show that application of mineral N fertilizer helps to maintain the mineralizable N content of the soil, which has been accumulated in the course of long-term intensive crop production, by adding N to the soil organic pool and simultaneously reducing the supply of soil N to the plants.     

Nitrogen-15 balances and nitrogen fertilizer use efficiency in upland rice

Field experiments were conducted in the 1984 and 1985 wet seasons to determine the effect of N fertilizer application method on¹⁵N balances and yield for upland rice (Oryza sativa L.) on an Udic Arguistoll in the Philippines. The test cultivars were IR43 and UPLRi-5 in 1984 and IR43 in 1985. Unrecovered¹⁵N in¹⁵N balances for 70 kg applied urea-N ha^–1, which represented N fertilizer losses as gases and movement below 0.5 m soil depth, ranged from 11–58% of the applied N. It was lowest (11–13%) for urea split applied at 30 days after seeding (DS) and at panicle initiation (PI), and highest (27–58%) for treatments receiving basal urea in the seed furrows. In all treatments with basal-applied urea, most N losses occurred before 50 DS.Heavy rainfall in 1985 before rice emergence resulted in large losses of native soil N and fertilizer N by leaching and possibly by denitrification. During the week of seeding, when rainfall was 492 mm, 91 kg nitrate-N ha^–1 disappeared from the 0.3-m soil layer in unfertilized plots. Although rainfall following the basal N application was less in 1984 than in 1985, the losses from basal applied urea-N were comparable in the two years. Daily rainfall of 20–25 mm on 3 of the 6 days following basal N application in 1984 may have created a moist soil environment favorable for ammonia volatilization.In both years, highest grain yield was obtained for urea split-applied at 30 DS and at PI. Delayed rather than basal application of N reduced losses of fertilizer N and minimized uptake of fertilizer N by weeds.     

Effects of different levels of chemical Nitrogen (urea) onAzolla and Blue-green algae intercropping with rice

Application of higher levels (60 and 90 kg N ha^–1) of nitrogen fertilizer (Urea) inhibited the growth ofAzolla pinnata (Bangkok) and blue-green algae (BGA) though the reduction was more in BGA thanAzolla. Inoculation of 500 kg ha^–1 of freshAzolla 10 days after transplanting (DAT) in the rice fields receiving 30, 60 and 90 kg N ha^–1 as urea produced an average of 16.5, 15.0 and 13.0 t ha^–1 fresh biomass ofAzolla at 30 DAT, which contained 31, 31 and 27 kg N ha^–1, respectively. The dry mixture of BGA (60%Aulosira, 35%Gloeotrichia and 5% other BGA on fresh weight basis) inoculated in rice field 3 DAT at a rate of 10 kg ha^–1 showed a mat formation at 80 DAT with an average fresh biomass of 8.0, 5.8 and 4.2 t ha^–1 containing 22, 17 and 12 kg N ha^–1, respectively with those N fertilizer doses.Application ofAzolla showed positive responses to rice crop by increasing the panicle number and weight, grain and straw yields and nitrogen uptake in rice significantly at all the levels of chemical nitrogen. But, the BGA inoculation had a significant effect on the grain and straw yields only during the dry season in the treatment where 30 kg N was applied. During the wet season and in the other treatments performed during the dry season no significant increase in yields, yield components and N uptake were observed with BGA.The intercropping ofAzolla and rice in combination with 30, 60 and 90 kg N ha^–1 as urea showed the yields, yield attributes and nitrogen uptake in rice at par with those obtained by applying 60, 90 and 120 kg N ha^–1 as urea, respectively but, the BGA did not. The analysis of soil from rice field after harvest showed thatAzolla and BGA intercropping with rice in combination with chemical fertilizer significantly increased the organic carbon, available phosphorus and total nitrogen of soil.     

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.     

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.     

Nitrogen use efficiency by maize as affected by a mucuna short fallow and P application in the coastal savanna of West Africa

Maize is the primary food crop grown by farmers in the coastal savanna region of Togo and Benin on degraded (rhodic ferralsols), low in soil K-supplying capacity, and non-degraded (plinthic acrisols) soils. Agronomic trials were conducted during 1999–2002 in southern Togo on both soil types to investigate the impact of N and P fertilization and the introduction of a mucuna short fallow (MSF) on yield, indigenous N supply of the soil, N recovery fraction and internal efficiency of maize. In all plots, an annual basal dose of 100 kg K ha^–1 was applied to the maize crop. Maize and mucuna crop residues were incorporated into the soil during land preparation. Treatment yields were primarily below 80% of CERES-MAIZE simulated weather-defined maize yield potentials, indicating that nutrients were more limiting than weather conditions. On degraded soil (DS), maize yields increased from 0.4 t ha^–1 to 2.8 t ha^–1 from 1999 to 2001, without N or P application, in the absence of MSF, with annual K application and incorporation of maize crop residues. Application of N and P mineral fertilizer resulted in yield gains of 1–1.5 t ha^–1. With MSF, additional yield gains of between 0.5 and 1.0 t ha^–1 were obtained at low N application rates. N supply of the soil increased from 10 to 42 kg ha^–1 from 1999 to 2001 and to 58 kg N ha^–1 with MSF. Application of P resulted in significant improvements in N recovery fraction, and greatest gains were obtained with MSF and P application. MSF did not significantly affect internal N efficiency, which averaged 45 kg grain (kg N uptake)^–1. On non-degraded soils (NDS) and without N or P application, in the absence of MSF, maize yields were about 3 t ha^–1 from 1999 to 2001, with N supply of the soil ranging from 55 to 110 kg N ha^–1. Application of 40 kg P ha^–1 alone resulted in significant maize yield gains of between 1.0 (1999) and 1.5 (2001) t ha^–1. Inclusion of MSF did not significantly improve maize yields and even reduced N recovery fraction as determined in the third cropping year (2001). Results illustrate the importance of site-specific integrated soil fertility management recommendations for the southern regions of Togo and Benin that consider indigenous soil nutrient-supplying capacity and yield potential. On DS, the main nutrients limiting maize growth were N and probably K. On NDS, nutrients limiting growth were mainly N and P. Even on DS rapid gains in productivity can be obtained, with MSF serving as a means to allow farmers with limited financial means to restore the fertility of such soils. MSF cannot be recommended on relatively fertile NDS.     

An economic evaluation of a long-term experiment on phosphorus and manure amendments to sandy Sahelian soils: Using a stochastic dominance model

Poor fertility status of sandy Sahelian soils represents a major constraint to cereal and legume production. Soil amendment options were evaluated, using a stochastic efficiency framework. Dominance analyses showed that in the presence of annual applications of 30 kg N ha^–1 and 30 kg K ha^–1, efficient soil amendment options comprise of either the annual application of 8.7 kg P ha^–1 in the form of single superphosphates in combination with 5 tonnes manure ha^–1 applied every three years or the annual application of 17.5 kg P ha^–1 in the form of single superphosphates. Choice between these two efficient options depends on the availability of manure, deficiencies in sandy soils and farmer resource endowments.Submitted as JA no. 1133 by the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT).     

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.     

Alfalfa response to lime,phosphorus, potassium,magnesium, and molybdenum on acid ultisols

Alfalfa (Medicago sativa L.) is a high protein forage, cultivated widely in young, fertile soils. There is considerable potential for alfalfa production in areas with acidic, highly weathered soils, but few field studies on fertility requirements under these conditions have been published.Two field trials were conducted on ultisols to study the effects of lime, P, K, Mg and Mo on alfalfa growth and tissue composition. A trial with three rates of calcitic lime (0, 2400, and 3800 kg ha^–1) and P (0, 25, and 50 kg ha^–1) and two rates each of K (20 and 200 kg ha^–1 the first year, 250 and 500 kg ha^–1 in subsequent years), Mg (36 and 106 kg ha^–1) and Mo (0 and 0.25 kg ha^–1) was conducted on an Appling coarse sandy loam (Typic Hapludult). Another factorial experiment with three levels each of lime (0, 2000, and 4,000 kg ha^–1), P (0, 100, and 200 kg ha^–1), and K (0, 150, 300 kg ha^–1) was conducted on a Davidson sandy clay loam (Rhodic Paleudult).Application of lime or P resulted in increased dry matter (DM) production at both locations. Liming also raised plant tissue N concentration. Addition of Mo had no effect on DM production or on foliar composition. Addition of K depressed soil Mg, plant tissue Mg, and plant Mg uptake at both locations. On the Davidson soil DM increased when K was applied, but on the Appling soil K increased DM production only where Mg was also added. Addition of Mg decreased K uptake and depressed DM production unless K was also added.The observed antagonism between K and Mg is of importance for alfalfa production in highly weathered soils. Successful alfalfa production in these soils is unlikely unless attention is paid to the balance between these two nutrients. Raising soil pH increased foliar N concentration affecting forage quality as well as DM production.Contribution from the Dept. of Agronomy, Univ. of Georgia, Athens, GA 30602.     

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     

Uptake of NPK and yield of rainfed groundnut (Arachis hypogaea L.)

Experiments were conducted on sandy loam soils of Tirupati campus of Andhra Pradesh Agricultural University for two rainy seaons of 1980 and 1981 to study the effect of split application of NPK fertilizers on Spanish bunch groundnut. The fertilizer doses were 40 N, 20 P and 40 K kg ha^–1 in 1980 and 30 N, 10 P and 25 K kg ha^–1 in 1981.In 1980, uptake of N (48 kg ha^–1), P (7 kg ha^–1) and K (37 kg ha^–1) was maximum with the application of 10 N, 5 P and entire 40 K kg ha^–1 as basal and 30 N and 15 P kg ha^–1 at 30 days after sowing, leading to highest pod yield (0.76 t ha^–1). In 1981, application of 20 N, 10 P and 25 K kg ha^–1 as basal dose and 20 N kg ha^–1 at 30 days after seeding resulted in highest uptake of N (114 kg ha^–1), P (17 kg ha^–1) and K (58 kg ha^–1) and hence the pod yield (2.36 t ha^–1).Differences in the uptake of NPK and pod yield in 1980 and 1981 was due to variation in total rainfall and its distribution during the crop period. Rainfall was equally distributed throughout the crop period in 1981, whereas there were two prolonged dry spells of more than 40 days in 1980.