Banding increases effectiveness of fertilizer P for alfalfa production

A field experiment was conducted from 1992 to 1996 on an existing alfalfa (Medicago sativa Leyss) stand located on a P-deficient Black Chernozem (Typic Boroll) soil at Ponoka, Alberta, to compare the effectiveness of broadcasting (spread over the soil surface) versus banding (1.5 cm wide band placed 5 cm deep and 15 cm apart, using a coulter-type disc drill) of annual and one-time applications of P fertilizer on dry matter yield (DMY), P-use efficiency of applied P (PUE), protein yield (PY), recovery of fertilizer P (PR), net returns (NR) and non-renewable energy performance of alfalfa hay. There was a marked increase in DMY and PY from all the P application treatments in all the five years. Banding produced greater increase in DMY and PY than broadcasting, with both the annual (by 954 kg DMY ha^–1 and 205 kg PY ha^–1) and one-time application (by 742 kg DMY ha^–1 and 173 kg PY ha^–1) applications. The PUE (averaged across P rates and years) was greater with banding as compared to broadcasting by 58 kg DMY kg^–1 P ha^–1 for annual applications, and by 47 kg DMY kg^–1 P ha^–1 for one-time applications. In the same order, PR values were 16.0 and 12.1% greater with banding than broadcasting. Despite the higher costs of banding than broadcasting, net returns were significantly higher with banding in nearly all years. The differences between banding and broadcasting were generally greater at lower than at higher P rates. Based on the 5-year means, annual and one-time P applications produced similar increase in DMY, PY, PUE, PR and NR. In contrast, non-renewable energy inputs were higher for banding than broadcasting, but energy use efficiency was similar for both methods of application. In conclusion, method of P placement had the greatest effect on DMY, PY, PUE, PR, NR and energy performance, whereas annual and one-time applications showed similar results. The results suggest that alfalfa forage productivity and profitability can be improved by banding the P fertilizer with a coulter type disc in comparison to the conventional application method of broadcasting.     

Effectiveness of alfalfa in reducing fertilizer N input for optimum forage yield, protein concentration, returns and energy performance of bromegrass-alfalfa mixtures

Grasses, when grown in association with legumes, may utilize some N fixed by the legumes resulting in improved forage dry matter and protein yield. Field experiments were conducted at Lacombe and Eckville, Alberta, Canada to determine the effectiveness of alfalfa (Medicago sativaLeyss) in reducing fertilizer N requirements for optimum forage dry matter yield (DMY), protein concentration (PC), net margins (returns above N fertilization and forage harvesting costs) and non-renewable energy performance of bromegrass (Bromus inermis Leyss)-alfalfa mixtures. Ammonium nitrate was applied in early spring of 1993 to 1995 at 0, 50, 100, 150 and 200 kg N ha⁻¹ to five bromegrass-alfalfa compositions (pure bromegrass; 2:1, 1:1 and 1:2 ratio of bromegrass:alfalfa; and pure alfalfa) seeded in the summer of 1992. In the zero-N treatment, DMY was lowest in pure bromegrass stands, and increased substantially when alfalfa was grown in association with bromegrass. There was a marked increase in DMY from the application of N fertilizer in pure bromegrass stands, but the increase was much less in the mixed stands. There was a significant increase in PC in forage when bromegrass was grown in a mixture with alfalfa compared to bromegrass alone. Net margins were much greater from mixed stands than from pure bromegrass. In pure bromegrass stands, net margins increased with increasing N rates up to 200 kg N ha⁻¹, but equivalent net margins were usually attained without fertilizer N in bromegrass-alfalfa mixtures as low as 2:1. Energy performance of pure bromegrass stands was substantially improved by including alfalfa in the stands, whereas application of N fertilizer caused a strong and steady decline in energy use efficiency. Our findings indicate that seeding alfalfa in mixed stands with bromegrass can generate savings in N fertilizer (for pure bromegrass stands) equivalent to about 100 kg N ha⁻¹ or more, without any detrimental effect on forage yield, forage quality or net earnings. However, the short-lived nature of alfalfa in bromegrass-alfalfa mixtures remains a cautionary concern. Thus, producers should also adopt management practices that enhance longevity of alfalfa to maximize long-term benefits of using grass-legume mixtures. This revised version was published online in November 2006 with corrections to the Cover Date.     

Impact of different forms of N fertilizer on N2O emissions from intensive grassland

Nitrous oxide (N₂O) emissions were measured over two years from an intensively managed grassland site in the UK. Emissions from ammonium nitrate (AN) and urea (UR) were compared to those from urea modified by various inhibitors (a nitrification inhibitor, UR(N), a urease inhibitor, UR(U), and both inhibitors together, SU), as well as a controlled release urea (CR). N₂O fluxes varied through time and between treatments. The differences between the treatments were not consistent throughout the year. After the spring and early summer fertilizer applications, fluxes from AN plots were greater than fluxes from UR plots, e.g. the cumulative fluxes for one month after N application in June 1999 were 5.2 ± 1.1 kg N₂O-N ha^–1 from the AN plots, compared to 1.4 ± 1.0 kg N₂O-N ha^–1 from the UR plots. However, after the late summer application, there was no difference between the two treatments, e.g. cumulative fluxes for the month following N application in August 2000 were 3.3 ± 0.7 kg N₂O-N ha^–1 from the AN plots and 2.9 ± 1.1 kg N₂O-N ha^–1 from the UR plots. After all N applications, fluxes from the UR(N) plots were much less than those from either the AN or the UR plots, e.g. 0.2 ± 0.1 kg N₂O-N ha^–1 in June 1999 and 1.1 ± 0.3 kg N₂O-N ha^–1 in August 2000. Combining the results of this experiment with earlier work showed that there was a greater N₂O emission response to rainfall around the time of fertilizer application in the AN plots than in the UR plots. It was concluded that there is scope for reducing N₂O emissions from N-fertilized grassland by applying UR instead of AN to wet soils in cool conditions, e.g. when grass growth begins in spring. Applying UR with a nitrification inhibitor could cut emissions further.     

Nitrate leaching in temperate agroecosystems: sources, factors and mitigating strategies

Nitrate (NO₃ ^–) leaching from agriculturalproduction systems is blamed for the rising concentrations ofNO₃ ^– in ground- and surface-waters around the world.This paper reviews the evidence of NO₃ ^– leachinglosses from various land use systems, including cut grassland, grazed pastures,arable cropping, mixed cropping with pasture leys, organic farming,horticultural systems, and forest ecosystems. Soil, climatic and managementfactors which affect NO₃ ^– leaching are discussed.Nitrate leaching occurs when there is an accumulation ofNO₃ ^– in the soil profile that coincides with or isfollowed by a period of high drainage. Therefore, excessive nitrogen (N)fertilizer or waste effluent application rates or N applications at the wrongtime (e.g. late autumn) of the year, ploughing pasture leys early in the autumn,or long periods of fallow ground, can all potentially lead to highNO₃ ^– leaching losses. N returns in animal urine havea major impact on NO₃ ^– leaching in grazed pastures.Of the land use systems considered in this paper, the potential for causingNO₃ ^– leaching typically follow the order: forest< cut grassland < grazed pastures, arable cropping < ploughing ofpasture < market gardens. A range ofmanagement options to mitigate NO₃ ^– leaching isdescribed, including reducing N application rates, synchronizing N supply toplant demand, use of cover crops, better timing of ploughing pasture leys,improved stock management, precision farming, and regulatory measures. This isfollowed by a discussion of future research needs to improve our ability topredict and mitigate NO₃ ^– leaching.     

Changes in mineral N, microbial biomass and enzyme activities in different soil depths after surface applications of dairy shed effluent and chemical fertilizer

A field experiment was conducted to determine the effects of surface applications of dairy shed effluent (DSE) (effluent collected from a dairy milking shed and consists of dung, urine and water) or chemical fertilizer (NH₄Cl) on N dynamics, microbial biomass C and N and extracellular enzyme activities (protease, deaminase and urease) in different soil depths. The DSE and NH₄Cl were applied to pasture soil at an equivalent rate of 200 kg N ha^–1in May and November 1996, as autumn and late spring applications, respectively. Soil samples taken from different soil depths following the autumn application were analyzed for inorganic N, microbial biomass C and N and enzyme activities, while soil samples taken following the late spring application were analyzed for inorganic N only. The soil NH₄ ⁺concentration, soluble organic C, protease, deaminase and urease activities, and microbial biomass C and N significantly increased in the 0–5 cm soil depth soon after the application of DSE. During the first 30 days, the soluble organic C, microbial C and N and protease activity also increased in the 10–20 cm, while there was no such increase in deaminase and urease activities below 10 cm soil depth. After day 30, the microbial and enzyme activities decreased in the surface as well as in the sub-surface layers possibly due to the exhaustion of the available carbon substrates but remained higher compared to the NH₄Cl and control. The NH₄Cl application, due to lack of organic substrates, had no effect on soluble organic C, protease or urease activities and biomass C. However, it did increase the deaminase activity and microbial biomass N. The NO₃ ^– concentration in lower soil depths of NH₄Cl treated soils was significantly higher than those in the DSE and control. This indicates that possible NO₃ ^– leaching were more after NH₄Cl addition than after DSE. N applied in autumn had higher potential for leaching than that applied in late spring because of increased drainage, lower pasture growth and N uptake during the winter period. Being a source of organic N, DSE showed better performance in maintaining higher pasture yield and N uptake than the NH₄Cl and the control. Pasture yield and N uptake were always higher following the spring application than the autumn application because of the optimal environmental condition during summer. These results showed that soil treated with DSE had higher enzyme activities and microbial biomass than soil treated with chemical fertilizers and this may result in longer availability of N for plant uptake and reduce the risk of N leaching losses.     

A microplot study of the fate of15N-labelled ammonium nitrate and urea applied at two rates to ryegrass in spring

Confined microplots were used to study the fate of¹⁵N-labelled ammonium nitrate and urea when applied to ryegrass in spring at 3 lowland sites (S1, S2 and S3). Urea and differentially and doubly labelled ammonium nitrate were applied at 50 and 100 kg N ha^–1. The % utilization of the¹⁵N-labelled fertilizer was measured in 3 cuts of herbage and in soil to a depth of 15 cm (soil_0–15).Over all rates, forms and sites, the % utilization values for cuts 1, 2, 3 and soil_0–15 were 52.4, 5.3, 2.4 and 16.0% respectively. The % utilization of¹⁵N in herbage varied little as the rate of application increased but the % utilization in the soil_0–15 decreased as the rate of application increased. The total % utilization values in herbage plus soil_0–15 indicated that losses of N increased from 12 to 25 kg N ha^–1 as the rate of N application was increased from 50 to 100 kg N ha^–1.The total % utilization values in herbage plus soil_0–15 over both rates of fertilizer N application were 84.1, 80.8 and 81.0% for urea compared with 74.9, 72.5 and 74.4% for all ammonium nitrate forms at S1, S2 and S3 respectively. Within ammonium nitrate forms, the total % utilization values in herbage plus soil_0–15 over both rates and all sites were 76.7, 69.4 and 75.7% for¹⁵NH₄NO₃, NH₄ ¹⁵NO₃ and¹⁵NH₄ ¹⁵NO₃ respectively. The utilization of the nitrate moiety of ammonium nitrate was lower than the utilization of the ammonium moiety.The distribution of labelled fertilizer between herbage and soil_0–15 varied with soil type. As the total utilization of labelled fertilizer was similar at all sites the cumulative losses due to denitrification and downward movement appeared to account for approximately equal amounts of N at each site.     

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.     

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.     

Light fraction organic N, ammonium, nitrate and total N in a thin Black Chernozemic soil under bromegrass after 27 annual applications of different N rates

Anadequate supply of N for a crop depends among others on the amounts of N thataremineralized from the soil organic matter plus the supply of ammonium andnitrateN already present in the soil. The objective of this study was to determine thebehaviour of light fraction organic N (LFN), NH₄-N, NO₃-Nand total N (TN) in soil in response to different rates of fertilizer Napplication. The 0–5, 5–10, 10–15 and 15–30cm layers of a thin Black Chernozemic soil under bromegrass(Bromus inermis Leyss) at Crossfield, Alberta, Canada,weresampled after 27 annual applications of ammonium nitrate at rates of 0, 56,112,168, 224 and 336 kg N ha^–1. The concentration andmass of TN and LFN in the soil, and the proportion of LFN mass within the TNmass usually increased with N rates up to 224 kg Nha^–1. The increase in TN mass and LFN mass per unit ofNadded was generally maximum at 56 kg N ha^–1 anddeclined with further increases in the rate of N application. The percentchangein response to N application was much greater for the LFN mass than for the TNmass for all the N rates and all soil depths that were sampled. Mineral N intheform of NH₄-N and NO₃-N did not accumulate in the soil at 112 kg N ha^–1 rates, whereas theiraccumulation increased markedly with rates of 168 kg Nha^–1. In conclusion, long-term annual fertilization at 112 kg N ha^–1 to bromegrass resulted insubstantial increase in the TN and LFN in soil, with no accumulation ofNH₄-N and NO₃-N down the depth. The implication of thesefindings is that grasslands for hay can be managed by appropriate Nfertilization rates to increase the level of organic N in soil.     

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.     

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     

The effects of a nitrification inhibitor on leaching losses and recovery of mineralized nitrogen by a wheat crop after ploughing-in temporary leguminous pastures

The effect of a nitrification inhibitor on the accumulation of ammonium (NH ₄ ⁺ -N) and nitrate (NO ₃ ^- -N) in the profile was investigated in two field experiments in Canterbury, New Zealand after the ploughing of a 4-year old ryegrass/white clover pasture in early (March) and late autumn (May). Nitrate leaching over the winter, and yield and N uptake of a following wheat crop were also assessed.The accumulation of N in the soil profile by the start of winter was greater in the March fallow (76–140 kg N ha^–1) than in the May fallow treatment (36–49 kg N ha^–1). The nitrification inhibitor dicyandiamide (DCD) did not affect the extent of net N mineralization, but it inhibited nitrification when applied to pasture before ploughing, especially at its depth of incorporation (100–200 mm). Nitrification inhibition in spring was greater when DCD was applied in May rather than in March due to its reduced degradation over the winter.Cumulative nitrate leaching losses were substantial from the March fallow treatment in both years (about 100 kg N ha^–1). A delay in the cultivation of pasture and the application of DCD both reduced nitrate leaching losses. When leaching occurred early in the winter (in 1991), losses were less when pasture was cultivated in May (2 kg N ha^–1) than when DCD was applied to pasture cultivated in March (68 kg N ha^–1). When leaching occurred late in the winter (in 1992), similar losses were measured from pasture cultivated in May (49 kg N ha^–1) and from DCD-treated pasture cultivated in March (57 kg N ha^–1).Grain harvest yield and N uptake of the following spring wheat crop were generally unaffected by the size of the N leaching loss over the winter. This was due to the high N fertility of the soil after four years of a grazed leguminous pasture.     

Nitrate distribution and accumulation in an Ustochrept soil profile in a long term fertilizer experiment

Distribution and accumulation of NO₃—N, down to 210 cm depth, in the soil profile of a long term fertilizer experiment were studied after 16 cycles of cropping (maize-wheat-fodder cowpea). The application of fertilizer N without P and K or in combination with only P resulted in higher NO₃—N concentration in the soil profile than the application of N with P and K. With an annual application of 320 kg N ha^–1 alone, a peak in NO₃—N accumulation occurred at 135 cm soil depth. However, with the application of NPK, no peak in NO₃—N distribution was discernible and its content at most of the sampling depths was either less than or equal to N and NP treatments. The annual application of 10 tons farm yard manure (FYM) per ha along with NPK resulted in a relatively lower NO₃—N content in the sub soil. The amount of NO₃—N accumulation in the soil profile decreased as the cumulative N uptake by the crops increased. Application of fertilizer amounts greater than that of the recommended (100% NPK) resulted in low percent N recoveries in crops and greater NO₃—N accumulation in the soil profile.     

Effectiveness of fall- versus spring-applied urea on barley

Field experiments were conducted in north-central and central Alberta to determine the effect of pellet size and depth of placement on yield and N uptake of barley from fall- and spring-applied urea. The application rate was 56 kg N ha^–1. Fall incorporated commercial urea (0.01 g) gave 792 kg ha^–1 lower yield and 15 kg ha^–1 less N uptake than similarly applied commercial urea in spring on the average for the five experiments. The effectiveness of fall-applied N tended to be greater with large urea pellets (2.5 g), especially when they were placed 15 cm deep. Specifically, the relative yield efficiency of fallversus spring-applied N was 77% when the larger pellets were placed 4 cm deep and 95% when placed 15 cm deep. However, large pellets were less effective than commercial urea when both were applied in spring at sowing or two weeks before.     

Fertigation versus broadcasting in an orange grove

A long-term experiment was carried out in a mature orange grove comparing broadcasting versus continuous application of nitrogen at three rates (80, 160, 280 kg ha^–1), 22 kg P ha^–1 and 126 kg K ha^–1 annually. The trees were irrigated with minispriklers wetting 70% of the soil area.The level of NO₃-N in the leaves varied according to the rate of N application. Leaf K and P content were not affected by fertilization. High N applications caused excess N in the soil solution. The rate of N application did not affect orange yield, fruit size or quality. Fertigation at 160 kg N ha^–1 caused higher yields than when the same amount of fertilizer was broadcast. At the high application rate, no differences between modes of application were found.This study was initiated by A. Bar-Akiva, who died suddenly early in 1986. Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. No 2104-E, 1987 series.(deceased)     

Slow-release urea fertilizers — effect on floodwater chemistry,ammonia volatilization and rice growth in an alkali soil

In experiments with transplanted rice (Oryza sativa L.) at the Central Soil Salinity Research Institute, Karnal, India, two methods of application of granular urea, wholly as basal dose U(W) or in splits U(S) were compared with deep, point placement (8 cm) of urea supergranules and broadcast application of two slow-release sources, sulphur-coated urea (SCU) and lac-coated urea (LCU). Comparisons were made in wet season 1984 and 1985 on the basis of ammoniacal N concentration and pH of floodwater, ammonia volatilization, rice yield and N uptake.In 1984 the highest peak concentrations of ammoniacal N (AN) in the floodwater, > 12g m^–3, and ammonia volatilization losses 54% of applied N were produced in U(W). Application of N in splits U(S) reduced peak AN levels 5g m^–3 and losses to 45.1%. LCU was ineffective in reducing peak AN levels ( 7.5g m^–3) or losses (43.6%). However SCU and USG were effective in reducing peak AN levels to < 2g m^–3 and N losses to 16.9 and 3.4% respectively. Total ammonia volatilization losses as well as the initial rate of loss correlated very well with the peak levels (second day) of AN, NH₃ (aq.) as well as equilibrium vapour pressure of NH₃. Floodwater pH was between 9.5 and 10.0.Split application of granular urea was generally more efficient in terms of yield and N recovery (41.4%, average of two years) as compared to whole application (29.5%). LCU was ineffective in improving grain yields or N recovery (30.9%). SCU was ineffective in improving grain yields but improved N recovery to 57.9%., USG increased grain yields only in first year by 19% over U(S) and improved N uptake to 60.5%. A negative linear relationship was established between N uptake by rice at harvest and AN levels in floodwater two days after fertilization which can be used as an index to evaluate fertilizers.     

Dryland wheat yield dependence on rainfall,applied N and mulching in preceding maize

To evaluate the response of dryland wheat (Triticum aestivum L.) to mulching in preceding maize and fertilizer N application field experiments were conducted for six years (1980–86) with maize-wheat sequence on a sandy loam soil in northern India. Four rates of N application viz. 0, 40, 60 and 80 kg N ha^–1 in wheat were combined with three mulch treatments viz. no mulch (M₀), paddy straw mulch (M_p) and basooti (Premma mucronate) mulch (M_b) applied at the rate of 4 tons ha^–1 on dry weight basis applied three weeks before harvest of maize. Mulching (M_p and M_b) increased (profile) stored moisture at wheat seedling by 31 to 88 mm. M_b also increased NO₃-N content by 33 to 42 kg ha^–1 in 0–120 cm profile over M₀ and M_p. Over the years, M_p increased wheat yield by 11 to 515 kg ha^–1 and M_b by 761 to 879 kg ha^–1. Wheat yield response to mulching was related to rainfall pattern during its growth season. Significant response to mulching was obtained only in years when rainfall during vegetative phase of the crop was low. Amount and distribution of rainfall during two main phases of crop development affected the N use efficiency by wheat. On an average, each cm of rain substituted for 3.5, 4.6 and 6.5 kg of applied N ha^–1 under M₀, M_p and M_b, respectively. Split rainfall for two main phases of crop growth, available stored water at seeding, fertilizer N and profile NO₃-N content accounted for 89 per cent variability in wheat yield across years and mulching treatments.     

The effect of soil moisture on mineral nitrogen, soil electrical conductivity, and pH

Inorganic nitrogen in the soil is the source of N for non-legume plants. Rapid methods for monitoring changes in inorganic N concentrations would be helpful for N nutrient management. The effect of varying soil moisture content on soil mineral nitrogen, electrical conductivity (EC), and pH were studied in a laboratory experiment. Soil NO₃-N increased as soil water-filled pore space (WFPS) increased from 0 to 80 cm³ cm^–3. At soil moisture levels greater than 80 cm³ cm^–3, NO₃-N concentration declined rapidly and NH₄-N concentration increased, likely due to anaerobic conditions existing at higher WFPS levels. Soil pH did not change as soil moisture increased from 100 g kg^–1 to 400 g kg^–1 and increased from 6.2 to 6.6 at higher levels of soil moisture. Soil EC was correlated with soil mineral N concentration when measured in situ with a portable EC meter (R ²=0.85) or in the laboratory as 1:1 soil water slurries (R ²=0.92). Results suggest that EC can be used to rapidly detect changes in soil inorganic N status in soils where salts and free carbonates are not present in large amounts.     

The comparison of nitrogen use and leaching in sole cropped versus intercropped pea and barley

The effect of sole and intercropping of field pea (Pisumsativum L.) and spring barley (Hordeum vulgareL.) and of crop residue management on crop yield,NO₃ ^– leaching and N balance in the cropping systemwas tested in a 2-year lysimeter experiment on a temperate sandy loam soil. Thecrop rotation was pea and barley sole and intercrops followed by winter-rye anda fallow period. The Land Equivalent Ratio (LER), which is defined as therelative land area under sole crops that is required to produce the yieldsachieved in intercropping, was used to compare intercropping performancerelative to sole cropping. Crops received no fertilizer in the experimentalperiod. Natural ¹⁵N abundance techniques were used to determine peaN₂ fixation. The pea–barley intercrop yielded 4.0 Mg grainha^–1, which was about 0.5 Mg lowerthan theyields of sole cropped pea but about 1.5 Mg greater than harvestedin sole cropped barley. Calculation of the LER showed thatplant growth resources were used from 17 to 31% more efficiently by theintercrop than by the sole crops. Pea increased the N derived fromN₂fixation from 70% when sole cropped to 99% of the total aboveground Naccumulation when intercropped. However, based upon aboveground N accumulationthe pea–barley intercrop yielded about 85 kg Nha^–1, which was about 65 kg lower thansolecropped pea but about three times greater than harvested in sole croppedbarley.Despite different preceding crops and removal or incorporation of straw, therewas no significant difference between the subsequent non-fertilized winter-ryegrain yields averaging 2.8 Mg ha^–1, indicating anequalization of the quality of incorporated residue by theNO₃ ^– leaching pattern.NO₃ ^– leaching throughout the experimental periodwas61 to 76 kg N ha^–1. Leaching dynamics indicateddifferences in the temporal N mineralization comparing lysimeters previouslycropped with pea or with barley. The major part of this N was leached duringautumn and winter. Leaching tended to be smaller in the lysimeters originallycropped with the pea–barley intercrops, although not significantly differentfromthe sole cropped pea and barley lysimeters. Soil N balances indicated depletionof N in the soil–plant system during the experimental period, independent ofcropping system and residue management. N complementarity in the croppingsystemand the synchrony between residual N availability and crop N uptake isdiscussed.     

Anionic Clays as Potential Slow-Release Fertilizers: Nitrate Ion Exchange

Several nitrate containing anionic clays were synthesized at different temperatures and the kinetics of NO₃ ^– release were determined to test their suitability as slow-release N fertilizers. A sample (Mg:Al = 2:1) synthesized at 60°C with smaller particle size released 75, 86 and 100% of its NO₃ ^– in 1, 3 and 7 days, respectively when equilibrated with a simulated soil solution. On the other hand, the 175°C/2 hrs sample with larger particle size released 65, 77 and 84% of its nitrate in 1, 3 and 7 days, respectively. Another anionic clay (synthesized at 175°C/24 hrs) of higher charge density (Mg:Al = 2:1) containing NO₃ ^– was equilibrated with a 0.012 N NaCl or Na₂CO₃ to test the role of different anions in releasing the NO₃ ^– anion from the interlayers. The results showed that Cl^– released more NO₃ ^– than did CO₃ ^2– from this anionic clay after all the treatment times probably as a result of the CO₃ ^2– anion blocking the release of NO₃ ^– from the interior of the crystals. When a lower charge density (Mg:Al = 3:1) sample (synthesized at 175°C/48 hrs) was equilibrated with 0.02N solution of anions the release of nitrate was as follows: Cl^– < F^– < SO₄ ⁼ CO₃ ^2–. These results suggest that the divalent SO₄ ⁼ and CO₃ ^2– anions are more effective in the release of NO₃ ^– from this lower charge density anionic clay. Time-resolved structural analysis of NO₃ ^– exchange with CO₃ ^2– in the above anionic clay using synchrotron x-ray diffraction showed that ion exchange is rapid because of small crystal size and lower charge density. Thus the release of NO₃ ^– from anionic clays is an interplay among the type of anions present in soil solution, their concentration, pH of soil solution, the charge density and crystal size of anionic clay etc.