Use of nitrification inhibitors to improve recovery of mineralised nitrogen by winter wheat

Nitrification inhibitors were applied in September 1980, after ploughing of a grass ley, to prevent formation of NO_3-N which could be lost by leaching and denitrification. Laboratory tests indicated that nitrapyrin or etridiazole at 1 μg g soil^?1 and dicyandiamide (DCD) at 10 μg g^?1 could inhibit nitrification by approximately 40%, compared with untreated soil, for 10 weeks at 10°C. In the field, nitrapyrin, etridiazole and DCD had little effect on NH₄ and NO₃ levels in the soil throughout autumn and winter. In April uptake of mineralised N by wheat was greater in plots treated with DCD (but not with nitrapyrin or etridiazole) than in untreated plots. Spring fertiliser N applications (35 or 70 kg N ha^?1) increased ear numbers, as did the two rates of all inhibitors except etridiazole. At harvest, grain and straw yields were increased by both rates of DCD with and without fertiliser N in spring, but there were no consistent increases from nitrapyrin or etridiazole. The mean increases in N uptake by wheat grain plus straw were 12 and 15% for 5 and 20 kg ha^?1 DCD respectively. DCD could be of use in preventing losses of NO₃-N, particularly in situations where large amounts of N may be mineralised during autumn and would be liable to loss prior to crop uptake.     

The distribution in the soil of aqueous ammonia injected under grass

In an experiment with grassland, aqueous ammonia containing about 28% N was injected in rows 305 mm apart either in the autumn or in the spring. Two treatments supplied 126 and 502 kg N ha^?1. Soil representing a cross-section of one row was taken 3 days after injecting the ammonia in autumn and 8 or 9 days after injecting in spring. The plots receiving ammonia in the autumn were resampled in spring. The soil was divided into 51 × 51 mm sections and for the samples at the time of injection those sections close to the point of injection were further subdivided. Each section or sub-section was analysed for NH_4?N and NO_3?N. The array of values was used to produce a computer printout from which lines of equal concentration could be drawn by the procedure described in the appendix. With 126 kg N ha^?1 applied, maximum concentrations found were 900–1440 μg N g^?1, and these had decreased to 100 μg g^?1 at 20–30 mm from the area of maximum concentration. Similarly with 502 kg N ha^?1 maximum concentrations were 2360–3340 μg N g^?1 and the concentration had decreased to 100 μg g^?1 at 50 mm from the zone of maximum concentration. Therefore even with the very large application of fertiliser only a small part of the surface rooting zone contained a concentration of ammonia large enough to damage roots or adversely affect root growth. The zone of maximum concentration was always above the point of injection and usually to the side of the centre of the slit indicating that the aqueous ammonia tended to flow up and to one side of the slit, presumably because the soil closed rapidly behind the narrow injection tine. This shows that aqueous ammonia may not necessarily be effectively injected as deeply as the depth of slit might indicate. The soils resampled in the spring showed that much ammonium nitrogen remained, mostly concentrated round the zone of maximum concentration near the point of injection. Some ammonium had nitrified and nitrate was distributed more uniformly than ammonium, some had moved 300 mm deep. Soil containing most ammonia also contained more water than the bulk of soil. This soil was also plastic and structureless and the clay was deflocculated. The extra water may initially have come from the injected aqueous ammonia but was retained because of the changed structure.     

Distribution of nitrapyrin [2-chloro-6-(trichloromethyl)-pyridine] and 2-chloro-6-(dichloromethyl)-pyridine in red beet treated with nitrapyrin

In red beet (Beta vulgaris L. var. conditiva) the main degradation product of added nitrapyrin [2-chloro-6-(trichloromethyl)-pyridine] has been shown to be 2-chloro-6-(dichloromethyl)-pyridine. The distribution of these two compounds in beet was also studied. The highest content of nitrapyrin residues (dry weight) was found in the root tips and the petioles; the peel contained more than the leaf laminae or other parts of the root. The higher the nitrapyrin content, the higher was the ratio of nitrapyrin to its dechloro form. No clear linear correlation was observed between the content of nitrapyrin and its dechloro form. The amounts of nitrapyrin residues in beet treated with Ca(NO₃)₂ were smaller than in the respective samples of beet fertilised with urea or NH₄NO₃.     

Nitrous oxide emission from permanent grass swards

Emissions of nitrous oxide from permanent grass swards growing on monoliths of clay (Salop series) or silt loam (Bromyard series) soils contained in lysimeters (80 cm diameter, 135 cm deep), were measured between October 1977 and August 1980. With no added fertiliser nitrous oxide emissions were small (equivalent to 10–30 μg N m^?2 h^?1), but after application of nitrate fertiliser (400 kg N ha^?1 year^?1) during the spring and summer months, emissions increased to peak values ca 1000 μg N m^?2 h^?1. The peaks were associated with nitrogen applications and rainfall/irrigation events, but persisted only for 3–7 days. Nitrous oxide production in the soil was mostly restricted to the upper 30 cm of the soil profile. Total annual nitrous oxide losses amounted to 6–8 kg N ha^?1 from the Salop clay soil and 4–6 kg N ha^?1 from the Bromyard silt loam.     

Effect of drought and irrigation on the fate of nitrogen applied to cut permanent grass swards in lysimeters: Leaching losses

Nitrogen losses were measured in water draining from cut permanent grass swards growing in monolith lysimeters containing clay loam (Salop series) or silt loam (Bromyard series) soils. The swards were cut at 6-week intervals during the summer and were fertilised with calcium nitrate at rates of 0 and 400 kg N ha^?1 in each of five successive years (1977–81); in the first year the fertiliser was labelled with ¹⁵N. Four differing rainfall regimes were imposed from spring to autumn in each year. Mean annual losses of nitrogen by leaching from unfertilised swards were 3.8 kg N ha^?1 with mean nitrate-N concentrations in the water of about 1 mg N litre^?1. In fertilised lysimeters where rainfall distribution was that of the long-term average the mean annual total nitrogen losses were 41 kg N ha^?1 in the Salop soil and 15 kg N ha^?1 for the Bromyard soil; mean nitrate-N concentrations were 11.6 mg N litre^?1 and 5.1 mg N litre^?1, respectively. Losses of nitrogen and nitrate concentrations were similar to these quantities when irrigation increased the rainfall total to 120% of average. Where a drought was imposed for 2 weeks before and after each cut, mean nitrate-N concentrations increased to 20.3 mg N litre^?1 on Salop soil and 13.1 mg N litre^?1 on Bromyard soils; total annual nitrogen losses were 74 kg N ha and 33 kg N ha^?1, respectively. The largest losses were recorded when the drought period extended for four weeks before each cut and mean nitrate-N concentrations increases to 28.8 mg N litre^?1 on Salop soil and 34 mg N litre^?1 on Bromyard soil, with total annual nitrogen losses of 104 kg N ha^?1 and 109 kg N ha^?1, respectively. Losses of nitrogen derived from the fertiliser labelled with ¹⁵N were 7.3–8.4% of that applied in the Salop soil (29–33 kg N ha^?1), with little effect by the differing rainfall distributions. On the Bromyard soil, losses were 3.7% (14 kg N ha^?1) of the applied fertiliser in lysimeters not subjected to droughts. When the period of the drought extended before and after each cut, losses were 8.2% (32 kg N ha^?1) and increased to 17.9% (70 kg N ha^?1) when the drought period occurred entirely before each cut. Fertiliser nitrogen contributed 48–69% of the total nitrogen in drainage water from both soils in the first year.     

Quality of white cabbage yield and potential risk of ground water nitrogen pollution,as affected by nitrogen fertilisation and irrigation practices

BACKGROUND: The effect of different fertilisation (broadcast solid NPK application and fertigation with water‐soluble fertiliser) and irrigation practices (sprinkler and drip irrigation) on yield, the nitrate content in cabbage (Brassica oleracea var. capitata L.) and the cabbage N uptake was detected, in order to assess the potential risk for N losses, by cultivation on sandy–loam soil. The N rate applied on the plots was 200 kg N ha^?1. RESULTS: The highest yield (93 t ha^?1) and nitrate content (1256 mg kg^?1 DW) were found with treatments using broadcast fertilisation and sprinkler irrigation. On those plots the negative N balance (?30 kg N ha^?1) was recorded, which comes mainly from the highest crop N uptake (234 kg N ha^?1) indicating the lowest potential for N losses. CONCLUSION: In terms of yield quality and the potential risk for N losses, broadcast fertilisation combined with sprinkler irrigation proved to be the most effective combination among the tested practices under the given experimental conditions. The importance of adequate irrigation is also evident, namely in plots on which 50% drip irrigation was applied, the lowest yield was detected and according to the positive N balance, a higher potential for N losses is expected. Copyright © 2011 Society of Chemical Industry     

A lysimeter study of nitrate leaching, optimum fertilisation rate and growth responses of corn (Zea mays L.) following soil amendment with water-saving super-absorbent polymer

BACKGROUND: Nitrate leaching and the resulting groundwater contamination from intensive cereal production has become a major concern for long‐term farmland efficiency and environmental sustainability in northern China. The aim of this study was to evaluate a water‐saving super‐absorbent polymer (SAP) for minimising NO₃^? leaching from soil and optimising corn growth and yield. Thirty‐six undisturbed soil lysimeters were installed in a field lysimeter facility in drought‐affected northern China to study the growth and yield characteristics of summer corn (Zea mays L.) as well as the amount of NO₃–leaching losses under different fertiliser (standard, medium or 75% and low, or 50% of conventional fertilisation rate) and SAP (control, 0; level‐1, 15 kg ha^?1 and level‐2, 30 kg ha^?1) treatments. RESULTS: Corn yield fell by 19.7% under medium and 37.7% under low fertilisation; the application of SAP increased yield significantly by 44.4% on level‐1 and 80.3% on level‐2. Similarly, plant height, leaf area, number of grains as well as protein, soluble sugar and starch contents in the grain also increased with SAP treatment. Application of SAP at 30 kg ha^?1 plus half of conventional fertilisation can reduce maximum (64.1%) nitrate leaching losses from soil. CONCLUSIONS: Application of SAP at 30 kg ha^?1 plus only half the amount of conventional fertiliser rate (150 kg urea, and 50 kg each of superphosphate and potassium sulfate) would be a more appropriate practice both for minimising nitrate leaching and sustainable corn production under the arid and semiarid conditions of northern China. Copyright © 2011 Society of Chemical Industry     

Effects of genotype, soil type, year and fertilisation on sensory and morphological attributes of carrots (Daucus carota L.)

BACKGROUND: The aim of the study was to investigate the effects of variety, soil type and fertilisation, and the interactions between these factors, on yield and quality traits of carrots. RESULTS: Optimum fertilisation levels for yield and quality of grade one roots were found to be between 80 and 160 kg ha^?1 for nitrogen and between 0 and 120 kg ha^?1 for potassium depending on soil type and precipitation. Carrots grown in peat soil had the highest score for sweetness and the lowest scores for negatively associated characteristics such as bitterness, earthy flavour, terpene flavour and firmness. Nitrate content and the amounts of splitted and forked roots were lowest on sandy soil. Variety significantly affected number of grade 1 roots, dry matter, nitrate content and most of the sensory attributes tested. Interactions between variety, soil type and nitrogen fertilisation were found for most of the tested quality characteristics. CONCLUSION: The investigations showed that year and variety had the highest impact on the carrot quality attributes studied, whereas soil type and fertilisation had less influence. Peat soil and moderate fertilisation with N and K gave optimal sensory quality while sand soil gave optimal quality as regards morphological characters like splitting and forking of roots as well as nitrate content. Copyright © 2012 Society of Chemical Industry     

Red clover (Trifolium pratense L.) isoflavones: root phenolic compounds affected by biotic and abiotic stress factors

BACKGROUND: Phenolic compounds have recently received considerable attention for their ability to protect plant and human cells from oxidative stress‐induced damage. Red clover (Trifolium pratense L.) is a rich source of isoflavonoids with multiple potential protective functions. The aim of this study was to identify and characterise phenolic compounds in red clover roots by high‐performance liquid chromatography and mass spectrometry and to study the effects of stress factors and growth stage on root phenolics. RESULTS: A total of 28 phenolic compounds were tentatively identified in red clover roots. The most abundant phenolics in pot‐grown roots were formononetin glycoside malonate (G‐M) (1.51–4.26 mg g^?1), formononetin (2.21–3.57 mg g^?1) and biochanin A (1.73–2.17 mg g^?1), whereas field‐grown roots were rich in formononetin‐G‐M (3.90–4.27 mg g^?1), maackiain‐G‐M (2.35–3.02 mg g^?1) and pseudobaptigenin‐G‐M (1.80–2.58 mg g^?1). Concentrations were affected by the growth stage. Ozone exposure slightly affected the total phenolic content in roots and also had minor effects on individual compounds. CONCLUSION: Elevated ozone, cultivation regime and growth stage affected the levels of phenolics in red clover roots, suggesting sensitivity of root phenolics to biotic and abiotic stress conditions. The high levels of phenolics found in roots even in late autumn may be utilised in many applications. Copyright © 2009 Society of Chemical Industry     

Effect of drought and irrigation on the fate of nitrogen applied to cut permanent grass swards in lysimeters: Nitrogen balance sheet and the effect of sward destruction and ploughing on nitrogen mineralisation

Fuor years after ¹⁵N labelled fertiliser nitrogen (as Ca(NO₃)₂ and equivalent to 400 kg N ha^?1) was applied to permanent grass swards growing in lysimeter monoliths, approximately one-quarter remained immobilised in soil organic matter. In the intervening years similar but non-labelled applications were made. Although differing rainfall regimes applied during the experiment had significantly affected nitrogen uptake by plants and nitrate loss in drainage, they caused no significant effect on the tracer nitrogen remaining in the soil, the ranges were 85–97 kg N ha^?1 and 79–94 kg N ha^?1 respectively for the 135 cm deep clay and silt loam soil monoliths. Labelled nitrogen unaccounted for in crop, drainage or soil was presumed to have been denitrified. These losses averaged 62 and 49 kg N ha^?1 on the clay and silt loam soils respectively; again the differing rainfall regimes caused no significant differences. The ratio between estimates of labelled nitrogen denitrified and of annual nitroux oxide loss was approximately 9:1 for both soils. The conversion from permanent grass to winter wheat in autumn 1981, involving killing and then burying the sward, resulted in no pronounced increase in net mineralisation of labelled nitrogen. However, the balance between crop uptake and the quantity leached did change. Labelled nitrogen assimilated was less for the wheat (growing without addition of fertiliser nitrogen) than for the grass in its last year, and the quantity leached was considerably greater than under grass swards that were supplied with an average rainfall distribution. Following the first wheat harvest total nitrogen leached averaged 51 and 44 kg N ha^?1 on the clay and silt loam soils respectively. Rates of nitrous oxide emissions during the autumn following sward destruction were greater than in earlier years, but this enhanced loss was of short duration. The crop clearly benefited from the succession of nitrogen applications made to grass, as grain yield and total nitrogen uptake exceeded 7 t ha^?1 and 120 kg N ha^?1 respectively on both soils. These quantities exceed the national averages for winter wheat and are also considerably greater than for crops from lysimeters which received no nitrogen fertiliser throughout the experiment.     

Laboratory measurements of dry deposition of sulphur dioxide on to several soils from England and Wales

A laboratory method for measuring the dry deposition of sulphur dioxide (SO₂) on to soils is described. The effect of soil type on deposition velocity (v_g) was examined using samples of soils collected from 16 sites in England and Wales. Although the values of v_g measured for soils at field capacity did not differ significantly they were related to soil pH; thus they ranged from 0.422 cm s^?1 at pH 4.5 to 0.648 cm s^?1 at pH 7.5. Oven drying reduced v_g from an average value of 0.535 cm s^?1 for soils at field capacity to 0.264 cm s^?1. A large proportion of deposited SO₂ was recovered from the soil as sulphate S. At an atmospheric concentration of 36 μg SO₂ m^?3, about the mean for Great Britain, the input of sulphur through this process would be 10 kg ha^?1 in a 4-month fallow period.     

Unused fertiliser nitrogen in arable soils—its contribution to nitrate leaching

Nitrate present in arable soils in autumn is at risk to leaching during the following winter. To see whether unused nitrogen fertiliser was a major source of this nitrate, ¹⁵N-labelled fertiliser was applied to 11 winter wheat crops at rates of between 47 and 234 kg N ha^?1in spring. The experiments were on three contrasting soil types in south-east England. On average, 17′% of the N from spring-applied labelled fertiliser remained in the 0–23 cm soil layer at harvest (range, 7–36%) but only a small proportion was in inorganic forms (ammonium + nitrate). This was never more than 5 kg N ha^?1and averaged only 1·3% of the fertiliser N applied (range, 0·4–3·6 %). Between 79 and 98% of the inorganic N in soils at harvest was unlabelled, being derived from the mineralisation of organic N rather than from unused fertiliser. The amount of unlabelled N was much greater where wheat was grown after ploughing up grass or grass/clover leys than where it was grown in all-arable rotations. When wheat was grown without N fertiliser, soil inorganic N content at harvest was no lower than in plots given fertiliser at rates up to 234 kg N ha^?1. This work indicates that, for soil growing winter wheat, almost all of the nitrate at risk to leaching over the winter period comes from mineralisation of organic N, not from unused fertiliser applied in spring. Consequently, even a drastic reduction in N fertiliser use would have little effect on nitrate leaching.     

Effect of residual fertility and direct fertilisation on kernel,protein and oil yield of peanut (Arachis hypogaea L) grown in rice fallows

Kernel (2814–3467 kg ha^?1), protein (555–759 kg ha^?1) and oil (124–1556 kg ha^?1) yields of peanut (Arachis hypogaea L) varied significantly due to the residual effect of organic manures and inorganic fertilisers together. It was also observed that direct application of recommended fertilisers (25 N, 72 P₂O₅ and 37-5 K₂O kg ha^?1) gave the highest kernel (3669 kg ha^?1), protein (786 kg ha^?1) and oil (1606 kg ha^?1) yields. The reduction in kernel, protein and oil yield from the recommended level of fertilisers to half the recommended level of fertilisers was about 16, 15 and 12% while it was about 25, 33 and 27% with no fertiliser. Thus, the results revealed that the nutrients applied partly through organic manures and inorganic fertilisers to Kharif rice exhibits significant residual effects on the succeeding upland crop and hence the fertilisation must be considered not only for individual crops but also for the cropping system as a whole.     

Nitrous oxide emissions from two sites in Southern England during winter 1981/1982

Nitrous oxide fluxes from soil surfaces were measured during winter 1981/82 on two fallow sites, a loamy sand and a clay loam, that had been watered to field capacity and fertilised at the rate of 200 kg N ha^?1 on the 5 October 1981. Highest fluxes were obtained in the sampling period immediately after fertiliser application. They were in the range 3.5–20 g N₂O? N ha^?1 day^?1 on the loamy sand, and declined rapidly from a peak of almost 165 g N₂O? N ha^?1 day^?1 on the day following fertiliser application on the clay loam. The temperature during this period was in the range 6.5 to 14°C. As soil temperature declined during the sampling periods in December (?2 to 3°C) and February (4.5 to 6.5°C) and nitrate was leached in the subsoil, N₂O evolution became very low (<1 g N₂O? N ha^?1 day^?1). Rainfall over the whole sampling period from early October to mid-February was 282 mm. On both sites there was a very high degree of variability within the sites at any sampling time.     

Seedbed fertilizer requirements of winter oilseed rape

Thirty-four field experiments were carried out on the seedbed fertilizer requirements of winter oilseed rape in the main rape-growing areas of England and Scotland. Average seed yield was increased by seedbed N from 2.711 ha^?1 to 2.881 ha^?1 (when 200 kg ha^?1 N was given in spring). Economic analysis showed 60 kg ha^?1 as likely to be the most profitable rate of seedbed N for most situations. P fertilizer increased yield significantly on soils with low or moderate levels of available soil P but there was little response to K fertilizer on soils of high or medium K status and too few experiments on low K status soils to quantify requirements thereon. S application to the seedbed (as calcium sulphate) did not increase yield. Seedbed N decreased seed oil content slightly and not always significantly while P, K and S had no effect. Nutrient removal in the seed of an average 3 t ha^?1 crop would be 90 kg ha^?1 of N, 17 kg ha^?1 of P (40 kg ha^?1 P₂O₅) and 17 kg ha^?1 of K (20 kg ha^?1 K₂O).     

Short‐duration cassava genotypes for crop diversification in the humid tropics: growth dynamics,biomass, yield and quality

BACKGROUND: Short‐duration (6–7 months) cassava provides opportunities to smallholder farmers for effective utilisation of resources such as land, moisture and nutrients as well as diversification of enterprise and income. The variation in biomass production and partitioning, seasonal course of growth indices, yield, quality and nutrient uptake of ten short‐duration/early‐bulking genotypes of cassava and their impact on nutrient contents in soil in a lowland situation akin to rice fallow were examined in this study. RESULTS: Triploid 2–18 gave the highest yield (38.34 t ha^?1), followed by triploid 4‐2, Sree Vijaya, Sree Jaya and Vellayani Hraswa, which were on a par (30–32 t ha^?1). Vellayani Hraswa, Sree Vijaya and triploid 4‐2 had significantly higher tuberous root dry matter content (370–380 mg g^?1) and fairly higher starch content (270–280 mg g^?1). All genotypes except triploid 4‐2, triploid 2–18 and H‐165 had low cyanogen content (29.2–43.8 µg g^?1), well within the tolerable limit. Tuberous root dry matter and total dry matter production, crop growth rate, tuberous root bulking rate and harvest index at the last phase, number of tuberous roots, mean weight of tuberous roots and nutrient uptake showed significant positive correlations with tuberous root yield. Principal component analysis also showed a similar trend. CONCLUSION: The diploids Sree Vijaya, Sree Jaya, Vellayani Hraswa and Kalpaka are ideal for cultivation in rice fallow for food use owing to their high yield, good cooking quality and low cyanogen content. The triploids are better suited for industrial use owing to their high tuberous root dry biomass production. Copyright © 2009 Society of Chemical Industry     

The effect of plant development and environment on formononetin concentration in red clover (Trifolium pratense L.)

Formononetin concentration in red clover herbage, determined by high performance liquid chromatography, was assessed in field, greenhouse and growth cabinet experiments. Formononetin content decreased in Hungaropoly swards from 5.6 mg g^?1 DM when harvested in early May to 3.5 mg g^?1 DM when harvested in mid-June. In the regrowth the sward with the shortest regrowth period had the highest concentration content (6.8 mg g^?1). In a pot experiment from vegetative through to the ‘dying inflorescence’ stage, formononetin concentration declined by 57% due to both a reduction in the concentration in stems more than in leaves and an increase in the proportion of stems in the dry matter. A temperature regime of 23/15°C (day/night) advanced flower appearance and adversely affected growth rate compared with 17/13°C. The lower temperature regime resulted in a higher formononetin content in expanded leaves (28% increase, mean of two harvests) and expanding leaves (17% increase). Incubation with β-glucosidase increased the amount of formononetin extracted in the stems. Phosphate fertiliser reduced the concentration of formononetin, 96 kg P ha^?1 reducing formononetin content by 32%, relative to red clover grown in soil with a low P content. The results are discussed in the context of the grazing management of red clover swards.     

Reducing gaseous losses of nitrogen from cattle slurry applied to grassland by the use of additives

Losses of nitrogen (N) through ammonia (NH₃) volatilisation and denitrification were determined following the application of cattle slurry to grassland in autumn or spring. Denitrification was examined on two contrasting soils. A system of small wind tunnels was used to measure NH₃ loss and an acetylene inhibition technique for denitrification. Between 31 and 84% of the ammonium N (NH-N) applied in slurry was lost through NH₃ volatilisation. Acidifying the slurry to pH c 5.5 prior to application reduced these losses to between 14 and 57%. On a freely drained loam soil, denitrification from unacidified slurry applied in the autumn at 80 m³ ha^?1 was continuous throughout the winter, with the maximum rate of 0.91 kg N ha^?1 day^?1 occurring a few weeks after slurry application. The total denitrification losses were equivalent to about 29% of the NH-N applied for this treatment and 41% for the acidified slurry. The nitrification inhibitor dicyandiamide reduced the amount of N lost through denitrification by 70% when applied with the slurry at 25 kg ha^?1, by 55% at 20 kg ha^?1 and by 30% at 15 kg ha^?1. The nitrification inhibitor nitrapyrin did not appreciably reduce denitrification. Denitrification losses were consistently small from slurry applied to the freely drained loam soil in spring, or to a poorly drained, silty clay in autumn or spring. Neither nitrification inhibitor was of benefit in these situations.     

Inhibition of nitrification by nitrapyrin,carbon disulphide and trithiocarbonate

We have studied the behaviour of the nitrification inhibitors nitrapyrin (2-chloro-6-trichloromethyl pyridine) and carbon disulphide (CS₂), and of trithiocarbonate ion (CS₃^2?). Solutions of Na₂CS₃ in water or aqueous NH₃ are stable but when added to soil they decompose with evolution of CS₂, which in laboratory tests was complete within hours. In field experiments each material was injected simultaneously with aqueous NH₃ or aqueous urea. Nitrapyrin was held strongly on soil near the centre of the injected band of fertiliser N. It became fully effective only approximately two months after injecting grassland in November (1974 and 1975) with 375 kg N/ha, but approximately one month after injecting winter wheat with 100 kg N/ha in March (1976). In contrast CS₂ itself, or CS₂ generated by CS₃^2?, diffused rapidly from the injected band and markedly inhibited nitrification for up to three months after injecting grassland and up to one month after injecting winter wheat, but had no effect on nitrification later. The main practical implication of the work is that liquid fertilisers supplying NH₄-N may, if mixed with a trithiocarbonate, be injected into grassland in autumn, without risk of substantial nitrate leaching during winter. This extends the period suitable for injection and eases congestion of work normally done in spring.     

Interrelationship of nitrogen nutrition with maize (Zea mays) grain yield,nitrogen use efficiency and grain quality

Eight maize (Zea mays L) hybrids were grown under five N levels with or without the nitrification inhibitor, nitrapyrin (2-chloro-[6-trichloro-methyl] pyridine), to evaluate N interactions relative to yield performance, N use efficiency, grain protein concentration, and kernel texture. Results indicate that maize hybrids can be grouped into three categories based on grain yield: (1) low N-responsive types which reach their maximum yield with 134 kg ha^?1 of applied N; (2) intermediate types that respond to moderate N levels (134 to 201 kg N ha^?1); and (3) high N-responsive types that respond to higher levels of N (201 kg N ha^?1). High N-responsive types, in general, increased yield with nitrapyrin treatment at all levels of N. Crop N utilisation efficiency for high N-responsive hybrids decreased, but was static for low N-responsive hybrids as N fertiliser increased. In general, as the grain yield of a hybrid increased in response to N, the concentration of protein in the kernel increased; although grain yields and protein concentration are negatively correlated among hybrids. Increased kernel translucence, an indicator of kernel hardness induced by N fertiliser, correlated highly positive with zein proteins. Isoelectric focusing analysis showed that increases in zein were primarily due to a quantitative increase in α- and γ-zein polypeptides. This study indicates that hybrids are different in their N requirements for maximum yield. Low N conditions not only restrict grain yield but also affect kernel textural quality.