Use of nitrification inhibitors (neem and DCD) to increase N efficiency in maize-wheat cropping system

A 2-year field experiment was conducted to study the effects of the nitrification inhibitors dicyandiamide (DCD) and neem cake on the efficiency of applied prilled urea nitrogen in a maize-wheat cropping system. Prilled urea (PU), neem cake coated urea (NCU) and DCD blended urea (DCDU) were applied to maize at two levels (60 and 120 Kg N ha^–1) and two methods (all preplant and split) of N application along with a no-nitrogen control and their relative residual effect was studied on succeeding wheat grown with three levels of N as PU.In 1990 maize responded well to N up to 60 kg N ha^–1; at this level PU increased maize yield by 1.03 t ha^–1, whereas NCU and DCDU increased maize yield by 1.55 and 1.18 t ha^–1 over the control, which was equivalent to an application of 127 and 94 kg N ha^–1 as PU, respectively. Furthermore, when the results were averaged over two years of study, residual N from the application of NCU and DCDU at 60 kg N ha^–1 left after maize cropping increased the grain yield of the succeeding wheat crop grown with 60 kg N ha^–1 as PU by 1.97 and 1.68 t ha^–1, respectively, over a no nitrogen control or 60 kg N ha^–1 as PU applied to the maize. This was equal to an application of 96 and 82 kg N ha^–1 as PU to wheat.Thus, neem cake increased the efficiency of urea N applied to maize and benefits were also seen in the succeeding wheat yield in the maize-wheat cropping system.     

Effect of rates and sources of nitrogen application on yield and nutrient uptake of Citronella Java (Cymbopogon winterianus Jowitt)

Two field experiments were conducted for two crop cycles each of two years (1985–87 and 1986–88) on an entisols to study the effect of rate and sources of N application on yield and nutrient uptake of Citronella Java (Cymbopogon winterianus Jowitt). Fresh herbage and essential oil yields were significantly influenced by application of N up to 200 kg ha^–1 yr^–1, while tissue N concentration and N uptake increased only to 150 kg N ha^–1. The oil yields with Neem cake coated urea (urea granules coated with Neem cake) and urea super granules were 22 and 9% higher over that with prilled urea and urea supergranules were significantly increased up to 200 kg N ha^–1 while with Neem cake coated urea, response was observed only to 150 kg N ha^–1! Estimated recovery of N during two years from Neem cake coated urea, urea supergranules and prilled urea were 38, 31 and 21%, respectively.     

Nitrogen response of maize under temporary flooding

The adverse effect of temporary flooding on maize (Zea mays L.) yields and the nitrogen management required to mitigate the effect of flooding were studied for five years in field experiments on Choa sandy loam soil.Maize yields decreased with increase in duration of flooding and with decrease in the age of the crop at the time of flooding. Flooding periods exceeding 48 hours caused significant crop damage. The loss in yield on account of flooding was, however, less in 40-day old crops. A 24 hours flooding decreased grain yield by 17.7 and 3.9 per cent in 20-day and 40-day old crops respectively. Maximum yield loss amounted to 1.23 t ha^–1 of grains with 72 hours of flooding of 20-day old crop indicating that a younger crop is more prone to the deleterious effect of flooding.The nitrogen content of grains decreased significantly with increase in flooding period. A supplemental dose of 7 kg N ha^–1 as urea spray significantly increased grain yield. Soil application of supplemental nitrogen at the rate of 14 or 20 kg N ha^–1 enhanced the maize yield by 0.7 to 0.9 t ha^–1 under temporary flooded conditions. Spraying with urea solution increased nitrogen removed by the crop.Successive increments of 60 kg N ha^–1 gave an additional yields of 1.23, 1.01 and 0.41 t ha^–1 over the crop that received no nitrogen. Flooded maize responded to even higher rates of N fertilization than the dose of 120 kg N ha^–1 which is recommended in this region.     

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.     

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.     

Recovery of15N-labelled fertilizer by sugar beet—spring wheat and winter rye—sugar beet cropping sequences

The recovery of¹⁵N labelled ammonium fertilizer was studied during two cropping sequences: sugar beet—spring wheat and winter rye—sugar beet with the labelled N applied to the first crop of each sequence. The difference between fall and spring application was also investigated. For the first cropping sequence 100 kg N ha^–1 labelled with 11.4%¹⁵N atom excess (a.e.) was applied to the sugar beets. This labelled N was followed in the sugar beets, in the soil profile at harvesting time as well as in the spring wheat of the following year. The first crop of sugar beet recovered 43–46% of the applied N, with 26–29% remaining in the soil at harvesting time and 25–31% could not be accounted for. Of the residual N, less than 1% could be recovered by the next crop of spring wheat. For the second cropping sequence 50 kg N ha^–1 labelled with 11.5%¹⁵N a.e. was applied to the winter rye and followed in the winter rye and in the sugar beets of the following year. The recovery of the labelled fertilizer N applied to the winter rye of the second sequence was 20–27% and the sugar beets of the next year could only recover 2%. With respect to time of application, no difference in fertilizer N recovery was found between fall or spring application for the two sequences.     

The use of farmgate balances and soil surface balances as estimator for nitrogen leaching to surface water

Farmgate balances (FGBs), defined as the difference between nutrient input and nutrient output at farm level, are currently used as a tool to monitor changes in nitrogen (N) and phosphorus (P) leaching to groundwater and surface water. We postulate that the estimator value of FGBs for N and P leaching to groundwater and surface water depends on (1) the distribution of N and P surpluses over fields within farms, and (2) the partitioning of the surplus over the various nutrient loss pathways. In this study, we assessed intra-farm variability of N and P surpluses and its possible consequences on N leaching to surface waters. Furthermore, we investigated the effect of policies to decrease N and P surpluses at farm level on N and P surpluses at field level. FGBs were derived for six dairy farms in a hydrologically rather isolated polder with grassland on peat soil for three years (1999, 2000 and 2001). Soil surface balances (SSBs), defined as the differences between nutrient input and nutrient output at field level, were derived for the accompanying 65 fields for the same years. On average, FGB surpluses decreased from 271 kg N ha^–1 y^–1 and 22 kg P ha^–1 y^–1 in 1999 to 213 kg N ha^–1 y^–1 and 13 kg P ha^–1 y^–1 in 2001. Variances in N and P surpluses between fields per farm were compared with variances between farms. For N, variances between fields per farm exceeded variances between farms for all years. A non-linear model was fitted on the measured N loading of the surface water. This model showed that N leaching to surface water was underestimated by 5–46% if the variability in N surpluses between fields per farm was not taken into account. We concluded that estimation of N leaching to surface water, based on data at farm level, can lead to underestimation of the N leaching due to the large variability in N surpluses between fields per farm. The extent of this bias by a given distribution of N surpluses within farms was largely controlled by the partitioning of the N surplus over the various nutrient loss pathways, notably denitrification.     

Productivity of nitrogen fertilized plantain in intercropping systems

The investigation evaluated the productivity of plantain intercropped with cassava, cocoyam and yam, fertilized annually with 0, 320 and 480 kg N ha^–1 respectively. Yields from nitrogen fertilized intercrops were higher than those of unfertilized treatments. In plantain + cassava intercrop receiving 480 kg N ha^–1 plantain growth was suppressed. Plantain intercropped with yam and fertilized with 320 kg N ha^–1 matured early and produced better bunches than other treatments. Plantain + yam or cocoyam intercropping systems fertilized with 320 kg N ha^–1 were recommended because of improved plantain establishment and increased combined crop yields.     

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.     

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.     

Growth response,yield and yield components of upland cotton (Gossypium hirsutum L) as affected by rates and time of nitrogen application in the Nigerian savannah

Effects of rate and time of nitrogen fertilization on growth, yield and yield components of upland cotton (Gossypium hirsutum L) were studied in two years (1975–76). Four rates of nitrogen application (0, 26, 52 and 78 kg ha^–1) timed at 3 or 8 weeks after sowing were compared. Seed cotton yield components increased significantly with increased N application at least up to 52 kg N ha^–1, with yield increases between 49% and 73%. Seed cotton yield was influenced by treatments mainly through boll number. Both crop growth rate and fruiting were enhanced by nitrogen fertilization. Applying N at 8 weeks (flowering) favoured yield only slightly over that at 3 weeks (thinning), but improved crop growth and fruiting by about 64% and 24%, respectively. There were significant N rate × time interactions in favour of fertilization at flowering. Applying 52 kg N ha^–1 at 8 weeks seems best for cotton in the Nigerian savannah.     

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.     

Direct and residual effect of fertilizer zinc application on the yield and chemical composition of rice-wheat crops in an alkali soil

A field experiment was conducted on an alkali soil to evaluate the direct and the residual effect of six levels of zinc i.e. 0, 2.25, 4.5, 9.0, 18.0 and 27.0 kg Zn ha^–1 added either once to the first crop only or continuously to each crop on the growth, yield and chemical composition of plants grown in a rice-wheat cropping sequence. The soils were amended with gypsum applied at the uniform rate of 14 t ha^–1. Zinc was supplied as zinc sulphate. Application of zinc at the rate of 2.25 kg ha^–1 to both rice and wheat crops or an annual application of 4.5 kg Zn ha^–1 only to rice was found optimum for rice-wheat sequence. Higher zinc applications increased the availability of zinc in the soil and its content in the plants but did not increase crop yield. DTPA extractable zinc build up was more for zinc applied at the rate of 2.25 kg ha^–1 to each crop compared to a single zinc application of equivalent amount. Results of these studies have shown that continuous Zn application up to 27 kg Zn ha^–1 to each crop did not induce nutrient imbalances and had no adverse effect on crop yield.     

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.     

Changes in quantity of mineral nitrogen in three grassland soils as affected by intensity of nitrogen fertilization

Changes in quantity of soil mineral nitrogen down to a depth of 1 m in cloverfree grassland were monitored within one growing season and over successive growing seasons. Accumulation of mineral nitrogen in the soil occurred on permanent grassland with split application of nitrogen totalling more than 400 kg N ha^–1 yr^–1 and on young grassland, sown after arable crops, with applications of more than 480 kg N ha^–1 yr^–1. The relationship between the rate of nitrogen application minus nitrogen uptake, and accumulation of mineral nitrogen in the upper 50 cm of soil during each growing season is described.     

Residual effects of growing mungbean and uridbean on the yield and nitrogen uptake of a succeeding wheat crop

A two year field experiment was carried out at the Indian Agricutural Research Institute, New Delhi - 110012, India to assess the effect of mungbean (Vigna radiata L.) and uridbean (Vigna mungo L.) residues on the yield and N uptake of a succeeding wheat crop as compared to sorghum fodder. Sorghum produced 3.5–7.5 times more dry matter and removed 2–3 times more nitrogen than mungbean or uridbean during same duration (80 ± 10 days) of their growth. Without N application the grain yield of wheat following mungbean and uridbean (without residue incorporation) was 0.45 and 0.48 t ha^–1 more than the yield of wheat following sorghum fodder. These yields were equivalent to that predicted when 36 and 38 kg urea-N ha^–1, respectively, was directly applied to wheat. The residual effects of these grain legumes were higher when succeeding wheat was fertilized with 60 kg urea-N ha^–1; at this level mungbean and uridbean spared 52 and 43 kg urea-N ha^–1, respectively, in succeeding wheat. The residual effect of mungbean and uridbean further increased when their residue was incorporated in soil; with this practice they spared 94 and 115 kg urea-N ha^–1, respectively, without N application to wheat and 74 and 82 kg urea-N ha^–1, respectively, with an application of 60 kg urea-N ha^–1 to wheat.Mungbean and uridbean, without residue incorporation, increased aboveground plant-N uptake of succeeding wheat by 11.5–34.9 and 10.8–34.0 kg N ha^–1, respectively; whereas with residue incorporation, they increased aboveground plant-N content of succeeding wheat by 26.1–45.8 and 32.7–47.7 kg N ha^–1, respectively.The results of the present study indicate that there is both an indirect sparing effect and a direct residual effect of mungbean and uridbean on the nitrogen needs of succeeding wheat, more so when their residues are incorporated in soil.     

Mineral nutrition and fertilizer response of grain sorghum in India — A review over the last 25 years

Researches on the mineral nutrition and fertilizer response of grain sorghum (Sorghum bicolor (L) Moench) carried out during the last 25 years in India are reviewed here. In general, N,P,K, Fe and Mn concentrations in vegetative plant parts decreased with crop age, while the concentrations of Ca, Mg and Cu increased. The concentration of N and P increased in panicle or grains of sorghum with advance in crop age. The seasonal change for other nutrients has not, however, been studied.Accumulation and uptake of N,P, and K by grain sorghum were characterized. Usually N and P accumulated slowly compared with the rapid accumulation of K in early crop growth stage and vice-versa in later stages of growth. As against the sizable mass of N and P into panicle, K was partitioned into stalk.Fertilizer responses to N and P were observed throughout India. Improved varieties and hybrids of sorghum responded to N rates ranging from 60 to 150 kg N ha^–1, whereas a response to P application was observed up to 40 kg P ha^–1. Although responses to K application had been inconsistent, an increase in grain yield of sorghum was observed due to 33 kg K ha^–1. A balanced fertilizer schedule consisting of 120 kg N ha^–1, 26 kg P ha^–1, 33 kg K ha^–1 and 15–25 kg Zn50₄ ha^–1 is recommended for improved productivity of grain sorghum.It is concluded that systematic research efforts should be directed so as to identify problem soils showing deficiencies and toxicities of different nutrients. Characterization of the seasonal changes in the concentration and uptake of different nutrients and determination of critical concentration and hidden hunger of different nutrients in plant tissues would lead to the recommendation of balanced fertilization for different sorghum-growing regions in India.A part of the paper presented in the Silver Jubliee Conference of Indian Society of Agronomy held at H.A.U., Hissar (India) in March, 1981     

Response of tomato to nitrogen fertilization and irrigation frequencies in a semi-arid tropical soil

The effect of different irrigation frequencies (5, 7 and 9 days interval) and N rates (0, 50, 100 and 150 kg N ha^–1) on applied N in tomato was studied in a field experiment during 3 growing seasons. The application of 100 kg N ha^–1 with irriga tion scheduled at 7 days interal resulted in significantly higher N uptake and recovery rate than the other combinations of N rate and irrigation frequencies studied.     

Fertilization of tropical rice: A case study on Bangkok plain

This study consisted of a survey on the nutritional status of rice plants in relation to nutrient application and yield in 70 farmers' fields in four provinces of Bangkok plain during the 1977 wet season. In addition a series of fertilizer experiments were carried out on rice experimental stations in the same provinces to study yield response to N and P fertilization and to develop a fertilizer recommendation system based on plant analysis.The average grain yield in the survey was 3.2 t ha^–1 and the early (high yielding varieties), medium (local) and late maturity (local) types yielded 3.3, 2.8 and 3.0 t ha^–1, respectively. The average amount of fertilizers applied to these maturity types were 33, 15 and 7 kg N ha^–1 and 15, 8 and 6 kg P ha^–1, respectively. Regression analysis indicated only a slight correlation between yield and any level of fertilizer application. On experimental stations yields over 6 t ha^–1 were obtained with applications of N over 100 kg ha^–1 and P over 22 kg ha^–1. Evaluation of nutritional status of plants based on plant analysis showed that in all provinces there were strong and widespread nutrient deficiences primarily of N and secondarily of P, and possibly of some other nutrients. Fertilizer application based on plant analysis gave high yield responses. It was concluded that the major constraints of yield on Bangkok plain are too low fertilizer application especially of N, and unbalanced fertilization of N and P.     

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.