Nitrogen fertilizer in leucaena alley cropping. II. residual value of nitrogen fertilizer and leucaena residues

Legume residues have been credited with supplying mineral nitrogen (N) to the associated cereal crop and improving soil fertility in the long term. Few studies using¹⁵N have reported the fate of legume N and fertilizer N in the presence of legume residues in soil-plant systems over periods of two years or longer. A field experiment was conducted in microplots to evaluate: (1) the residual value of the¹⁵N added in leucaena residues; (2) the residual value of fertilizer¹⁵N applied in the presence of unlabelled leucaena residues in the first year to maize over three subsequent years; and (3) the long-term fate of residual fertilizer and leucaena¹⁵N in a leucaena alley cropping system.There was a significant increase in maize production over three subsequent years after addition of leucaena residues. The residual effect of fertilizer N increased maize yield in the second year when N fertilizer was applied at 36 kg N ha^–1 in the first year in the presence of leucaena residues. Of the leucaena¹⁵N applied in the first year, the second, third and fourth maize crop recovered 2.6%, 1.8% and 1.4%, respectively. The corresponding values for the residual fertilizer¹⁵N were 0.7%, 0.4% and 0.3%. About 12–14% of the fertilizer¹⁵N added in the first year was found in the 200 cm soil profile over the following three years. This differed from the 38–41% of leucaena¹⁵N detected in the soil over the same period. Most of the residual fertilizer and leucaena¹⁵N in the soil was immobilized in the top 25 cm with less than 1% leached below 100 cm. More than 36% of the leucaena¹⁵N and fertilizer¹⁵N added in the first year was apparently lost from the soil-plant system in the first two years. No further loss of the residual leucaena and fertilizer¹⁵N was detected after two years.     

The effect of plant residues on plant uptake and leaching of soil and fertilizer nitrogen in a tropical red earth soil

Two field experiments, in which differing amounts and types of plant residues were incorporated into a red earth soil, were conducted at Katherine, N.T., Australia. The aim of the work was to evaluate the effect of the residues on uptake of soil and fertilizer N by a subsequent sorghum crop, on the accumulation and leaching of nitrate, and on losses of N.Stubble of grain sorghum applied at an exceptionally high rate (~ 18 000 kg ha^–1) reduced uptake of N by sorghum by 13% and depressed the accumulation of nitrate under a crop and particularly under a fallow.Loss of fertilizer N, movement of nitrate down the profile, and uptake by the crop was studied in another experiment after application of N as¹⁵NH₄ ¹⁵NO₃ to field microplots. By four weeks after fertilizer application 14% had been lost from the soil-plant system and by crop maturity 36 per cent had been lost. The pattern of¹⁵N distribution in the profile suggested that losses below 150 cm had occurred during crop growth. The recovery of¹⁵N by the crop alone ranged from 16 to 32 per cent. There was an apparent loss of N from the crop between anthesis and maturity. Residue levels common to sorghum crops in the region (~ 2000 kg ha^–1) did not significantly affect uptake by a subsequent sorghum crop, N losses, or distribution of nitrate in the profile.     

Nitrogen losses from fertilizers applied to maize, wheat and rice in the North China Plain

Ammonia volatilization, denitrification loss and total nitrogen (N) loss (unaccounted-for N) have been investigated from N fertilizer applied to a calcareous sandy loam fluvo-aquic soil at Fengqiu in the North China Plain. Ammonia volatilization was measured by the micrometeorological mass balance method, denitrification by the acetylene inhibition – soil core incubation technique, and total N loss by ¹⁵N-balance technique. Ammonia loss was an important pathway of N loss from N fertilizer applied to rice (30–39% of the applied N) and maize (11–48%), but less so for wheat (1–20%). The amounts of unaccounted-for fertilizer N were in the order of rice > maize > wheat. Deep placement greatly reduced ammonia volatilization and total N loss. Temperature, wind speed, and solar radiation (particular for rice), and source of N fertilizer also affect extent and pattern of ammonia loss. Denitrification (its major gas products are N₂ and N₂O) usually was not a significant pathway of N loss from N fertilizer applied to maize and wheat. The amount of N₂O emission (N₂O is an intermediate product from both nitrification and denitrification) was comparable to denitrification loss for maize and wheat, and it was not significant in the economy of fertilizer N in agronomical terms, but it is of great concern for the environment.     

Effect of the timing and rate of nitrogen fertilization on the growth and recovery of fertilizer nitrogen within the potato (Solanum tuberosum L.) crop

The effect of the timing of N fertilizer application on the uptake and partitioning of N within the crop and the yield of tubers has been studied in two experiments. In 1985 either none, 8 or 12 g N m^–2 was applied and in 1986 none, 12 or 18 g N m^–2. Fertilizer N was applied either at planting, around the time of tuber initiation or half at planting and the remainder in four foliar sprays of urea during tuber bulking.¹⁵N-labelled fertilizer was applied to measure the recovery of fertilizer N in the crops.There was an apparent pre-emergence loss of nitrate from the soil when N was applied at planting in 1986, thereby reducing the efficiency of fertilizer use. Applying the N at tuber initiation delayed and reduced the accumulation of N in the canopy compared with crops receiving all their fertilizer at planting. Foliar sprays of urea slightly increased both tuber yields and tuber N contents when compared to a single application at planting. The proportion of the fertilizer N recovered in the crop was little affected by the rate of N application, but a greater proportion of foliar-applied N was recovered than N broadcast at planting, due partly to pre-emergence losses of nitrate in 1986. It is suggested that late applications of N was foliar sprays can be of benefit to crops with a long growing season and reduce environmental losses of N.     

Fate of fertilizer nitrogen applied to wheat under simulated mediterranean environmental conditions

Triticum aestivumThe fate of fertilizer nitrogen applied to dryland wheat was studied in the greenhouse under simulated Mediterranian-type climatic conditions. Wheat, L., was grown in 76-cm-deep pots, each containing 50–70 kg of soil, and subjected to different watering regimes. Two calcareous clay soils were used in the experiments, Uvalde clay (Aridic Calciustoll) and Vernon clay (Typic Ustochrept). Fertilizer nitrogen balance studies were conducted using various¹⁵N-labeled nitrogen sources, including ammonium nitrate, urea, and urea amended with urea phosphate, phenyl phosphorodiamidate (a urease inhibitor), and dicyandiamide (a nitrification inhibitor). Wheat yields were most significantly affected by available water. With additional water during the growing period, the recovery of fertilizer nitrogen by wheat increased and the fraction of fertilizer nitrogen remaining in the soil decreased. In the driest regimes, from 40 to 65% of the fertilizer nitrogen remained in the soils. In most experiments the gaseous loss of fertilizer nitrogen, as estimated from unaccounted for¹⁵N, was not significantly affected by water regime. The¹⁵N not accounted for in the plant and the soil at harvest ranged from 12 to 25% for ammonium nitrate and from 12 to 38% for regular urea. Direct measurement of labeled ammonia loss from soil indicated that ammonia volatilization probably was the main N loss mechanism. Low unaccounted-for¹⁵N from nitrate-labeled ammonium nitrate, 4 to 10%, indicated that N losses due to denitrification, gaseous loss from plants, or shedding of anthers and pollen were small or negligible. Amendment of urea with urea phosphate to form a 36% N and 7.3% P product was ineffective in reducing N loss. Dicyandiamide did not reduce N loss from urea presumably because N was not leached from the sealed pots and denitrification was insignificant. Amendment of urea with 2% phenyl phosphorodiamidate reduced N loss significantly. However, band placement of urea at as 2-cm soil depth was more effective in reducing N loss than was amendment of broadcast urea with phenyl phosphorodiamidate.     

1. The chemistry and biology of flooded soils in relation to the nitrogen economy in rice fields

Response of lowland rice to sources and methods of nitrogen fertilizer application were summarized for more than 100 experiments. In about 2/3 of the experiments, the yield increase per kg of fertilizer N was judged to be relatively poor with best split applications of urea. Based on frequency distribution, sulfur coated urea and urea briquets or urea supergranules deep placed more often produced satisfactory yield increases than best split urea, but even with these sources/methods the yield increases were judged to be relatively poor in about 1/2 of the experiments. There is an enormous potential to increase rice production with no further increases in inputs of fertilizer N if we could learn to match the best method/source of fertilizer with the soil-crop management complex.About 60% of the yields with no fertilizer N were in the range of 2 to 4 t/ha. Based on the average yield response to urea, this is equivalent to about 100 kg of urea N. It would appear worthwhile to study ways to improve utilization of soil nitrogen since it is already in place on the land and apparently in fairly abundant amounts in many soils.About 50 experiments with¹⁵N fertilizers were summarized. In almost all cases, the uptake of tagged fertilizer was less than the net increase in N in the above ground matter. In about 2/3 of the experiments, the addition of fertilizer N increased soil N uptake more than 20% and in 1/3 of the experiments the uptake of soil N was increased more than 40%. These results lead to much uncertainty about practical interpretation and use of¹⁵N data.     

Urea-N uptake by dasheen (Colocasia esculenta L. Schott) in relation to the fertilizer placement method

Urea has become the most important N carrier in many parts of the world and its reaction when added to soil is unique in many ways. Two field experiments were therefore undertaken using¹⁵N to investigate the uptake efficiency of the added urea-¹⁵N which was banded in Experiment I and broadcast in Experiment II. In both experiments the uptake efficiencies were not affected by N-rate and cropping system (Exp. I) or crop residue management (Exp. II) and averaged 17.4 and 16.9% respectively. These low values were supported by evidences of high losses; high pH increases following urea application (volatilization), downward movement of N (leaching), and cycles of waterlogged and well drained conditions in the soil (de-nitrification). Evidence of leaching at least down to 30 cm in the profile was observed in the first experiment where urea was banded but not in experiment II where it was broadcast. The proportion of N in the crop that was derived from added urea (%Ndff) was 57.7% and 36.4% in experiments I and II respectively, suggesting that band application resulted in a higher proportion of the added N in the root zone compared to that for broadcast application. The results indicate the need to investigate other management strategies, such as higher application frequencies and placement closer to the root zone, in order to improve the uptake efficiency of added urea-N in upland rainfed dasheen.     

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

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

Recovery of 15N-labelled fertilizer applied to winter wheat and perennial ryegrass crops and residual 15N recovery by succeeding wheat crops under different crop residue management practices

The recovery of ¹⁵N-labelled fertilizer applied to a winter wheat (120 kg N ha^–1) and also a perennial ryegrass (60 kg N ha^–1) crop grown for seed for 1 year in the Canterbury region of New Zealand in the 1993/94 season was studied in the field. After harvests, ryegrass and wheat residues were subjected to four different residue management practices (i.e. ploughed, rotary hoed, mulched and burned) and three subsequent wheat crops were grown, the first succeeding wheat crop sown in 1994/95 to examine the effects of different crop residue management practices on the residual ¹⁵N recovery by succeeding wheat crops. Total ¹⁵N recoveries by the winter wheat and ryegrass (seed, roots and tops) were 52% and 41%, respectively. Corresponding losses of ¹⁵N from the crop-soil systems represented by un-recovered ¹⁵N in crop and soil were 12% and 35%, respectively. These losses were attributed to leaching and denitrification. The proportions of ¹⁵N retained in the soil (0-400 mm depth) at the time of harvest of winter wheat and ryegrass were 36% and 24%, respectively. Although the soil functioned as a substantial sink for fertilizer N, the recovery of this residual fertilizer by subsequent three winter wheat crops was low (1-5%) and this was not affected by different crop residue management practices.     

Uptake and balance of labelled fertilizer nitrogen by potatoes

Potatoes have a shallow rooting system. This can seriously affect the efficient use of fertilizer N. During two consecutive years, 1985 and 1986, a study was conducted on a commercial field to investigate the uptake of labelled N by potatoes under the recommended N rate and existing agricultural practices. The fertilizer efficiency, fertilizer distribution within the plant and soil and the total fertilizer balance were made using¹⁵NH₄ ¹⁵NO₃ 3.63 At. %¹⁵N excess. The recovery of the applied N-fertilizer in the whole plant was 25 and 56% for 1985 and 1986, respectively. The % Ndff and % Ndfs ranged between 30–40% and 60–70% respectively in both years. An important amount of fertilizer N was left in the soil after harvest. It reached 44 and 34% in 1985 and 1986, respectively.The total balance of the applied fertilizer N showed that up to 31 and 10% of the fertilizer N was lost during 1985 and 1986, respectively. The differences between the two growing seasons were mainly related to the method and timing of fertilizer N application and to the amount of rainfall.     

Nitrogen fertilizer in leucaena alley cropping. I. Maize response to nitrogen fertilizer and fate of fertilizer-15N

Field microplot experiments were conducted in the semi-arid tropics of northern Australia to evaluate the response of maize (Zea mays L.) growth to addition of N fertilizer and plant residues and to examine the fate of fertilizer¹⁵N in a leucaena (Leucaena leucocephala) alley cropping system, in which supplemental irrigation was used. Leucaena prunings, maize residues and N fertilizer were applied to alley-cropped maize grown in microplots which were installed in the alleys formed by leucaena hedgerows spaced 4.5 metres apart. The¹⁵N-labelled fertilizer was used to examine the fate of fertilizer N applied in the presence of mulched leucaena prunings and maize residues.Application of leucaena prunings increased maize yield while addition of N fertilizer in the presence of the prunings produced a further increase in maize production. There was a significant positive interaction between N fertilizer and leucaena prunings in increasing maize production. The addition of maize residues in the presence of N fertilizer and leucaena prunings decreased maize yield and N uptake and increased fertilizer¹⁵N loss from 38% to 47%. Maize recovered 24–79% of fertilizer¹⁵N in one cropping season, depending on application rate of N fertilizer and field management of plant residues. About 20–34% of fertilizer¹⁵N remained in the soil. More than 37% of fertilizer¹⁵N was apparently lost from the soil and plant system largely through denitrification when N fertilizer was applied at 40 kg N ha^–1 or more in the presence or absence of plant residues. Application of N fertilizer improved maize yield and increased the contribution of mulched leucaena prunings to crop production in the alley cropping system.     

Effect of climate on the recovery in crop and soil of15N-labelled fertilizer applied to wheat

Data was assembled from experiments on the fate of¹⁵N-labelled fertilizer applied to wheat (Triticum spp.) grown in different parts of the world. These data were then ranked according to the annual precipitation-evaporation quotient for each experimental location calculated from the average long-term values of precipitation and potential evaporation. Percentage recovery of¹⁵N fertilizer in crop and soil varied with location in accordance with the precipitation-evaporation quotient. In humid environments more¹⁵N fertilizer was recovered in the crop than in the soil, while in dry environments more¹⁵N fertilizer was recovered in the soil than in the crop. Irrespective of climatic differences between locations 20% (on average) of the¹⁵N fertilizer applied to wheat crops was unaccounted for at harvest. Most of the¹⁵N fertilizer remaining in the soil was found in the 0–30 cm layer. The most likely explanation of these differences is that wheat grown in dry environments has a greater root:shoot ratio than wheat grown in humid environments and, further, that the residue of dryland crops have higher C/N ratios. Both factors could contribute to the greater recovery of¹⁵N fertilizer in the soil in dry environments than in humid ones.     

The comparative effects of ammonium nitrate,urea or a combined ammonium nitrate/urea granular fertilizer on the efficiency of nitrogen recovery by perennial ryegrass

The comparative effects of ammonium nitrate (AN), urea or a combined 1:1 (w/w) AN/urea granular fertilizer with two different fillers (CaCO₃ or silica) were investigated on the efficiency of dry matter production and¹⁵N recovery by perennial ryegrass grown in pots under controlled environmental conditions.There was no significant difference between CaCO₃ and silica as the filler and therefore no indication that the presence of CaCO₃ in the pellet enhanced N loss from urea. Ammonium nitrate was the most efficient N source and urea the least efficient in terms of all the parameters studied. The¹⁵N budget in shoots, roots and soil indicated that only 60% of the nitrogen from urea was recovered at the end of the experiment compared with 95% for AN. However, the % recovery of¹⁵N from urea was increased by 17% in the presence of AN whereas the % recovery of AN was decreased by 19% in the presence of urea. The combined 1:1 (w/w) AN/urea source therefore gave intermediate yields between AN and urea alone. The results indicate that an interaction occurred between AN and urea in the granule.     

Movement and distribution of fertilizer nitrogen as affected by depth of placement in wetland rice

Experiments were conducted to monitor the movement and distribution of ammonium-N after placement of urea and ammonium sulfate supergranules at 5, 7.5, 10, and 15 cm. By varying depths of fertilizer placement, it is possible to determine the appropriate depth for placement machines. There were no significant differences in grain yields with nitrogen placed 5 and 15 cm deep. However, grain yields were significantly higher with deep placement of nitrogen than with split application of the fertilizer. The lower yields with split-applied nitrogen were due to higher nitrogen losses from the floodwater. The floodwater with split application had 78–98µg N ml^–1 and that with deep-placed nitrogen had a negligible nitrogen concentration.Movement of NH ₄ ⁺ -N in the soil was traced for various depths after fertilizer nitrogen application. The general movement after deep-placement of the ammonium sulfate supergranules was downward > lateral > upward from the placement site. Downward movement was prevalent in the dry season: fertilizer placed at 5–7.5 cm produced a peak of NH ₄ ⁺ -N concentration at 8–12 cm soil depth; with placement at 15 cm, the fertilizer moved to 12–20 cm soil depth. Fertilizer placed at 10 cm tended to be stable. In the wet season, deep-placed N fertilizer was fairly stable and downward movement was minimal.A substantially greater percentage of plant N was derived from¹⁵N-depleted fertilizer when deep-placed in the reduced soil layer than that applied in split doses. The percent N recovery with different placement depths, however, did not vary from each other. The results suggest that nitrogen placement at a 5-cm soil depth is adequate for high rice yields in a clayey soil with good water control. In farmers' fields where soil and water conditions are often less than ideal, however, it is desirable to place nitrogen fertilizer at greater depths and minimize NH ₄ ⁺ -N concentration in floodwater.     

Efficiency of nitrogen fertilizer in the sugarcane-vertical system in Guadeloupe according to growth and ratoon age of the cane

Sugarcane is one of the main economic resources of Guadeloupe (France). Cane grown on the island's vertisols shows nitrogen deficiency which is accentuated with each successive ratoon. This deficiency could partially explain the observed decrease in yield. The present study, based on the isotopic N method applied to different ratoons in the field, was aimed at: (i) diagnosing the problem in the crop environment itself; and (ii) quantifying the fertilizer-N balance. The results indicated that decrease in yield and N absorption by the cane was related to ratoon number. The real utilization coefficient for the fertilizer (RUC%) ranged from 6 and 34%, and a high proportion (30–40%) of fertilizer-N was immobilized in the soil (NiS%) after the annual crop cycle. The N absorbed by the cane was essentially derived from the soil. Rainfall at the beginning of (re)growth determined crop development and N supply to the crop. When the water requirements of the crop are satisfied, nitrogen supply and cane yield can be improved in two ways: (i) by increasing the efficiency of the applied N fertilizer (RUC% and NiS%); and (ii) by maintaining the soil's capacity to supply cane with N. This implies maintaining and, if necessary, upgrading the structural state of the vertisols.     

15N isotope dilution techniques to study soil nitrogen transformations and plant uptake

The use of¹⁵N as a tracer in soil/plant research is examined. The limitations of the so-called Ndff approach are discussed to show the need to consider not just the fate of the added label but also the path that was followed and the rate of the transformation. The development of¹⁵N isotope dilution techniques to determine gross rates of nitrogen transformation in soil is reviewed with some indications as to the further development of the approach.     

Fate of nitrogen fertilizer applied to lowland rice on a Sulfic Tropaquept

A field experiment was conducted on an acid sulfate soil in Thailand to determine the effect of N fertilization practices on the fate of fertilizer-N and yield of lowland rice (Oryza sativa L.). A delayed broadcast application of ammonium phosphate sulfate (16-20-0) or urea was compared with basal incorporation of urea, deep placement of urea as urea supergranules (USG), and amendment of urea with a urease inhibitor. Deep placement of urea as USG significantly reduced floodwater urea- and ammoniacal-N concentrations following N application but did not reduce N loss, as determined from an¹⁵N balance, in this experiment where runoff loss was prevented. The urease inhibitor, phenyl phosphorodiamidate (PPD), had little effect on floodwater urea- and ammoniacal-N, and it did not reduce N loss. The floodwater pH never exceeded 4.5 in the 7 days following the first N applications, and application of 16-20-0 reduced floodwater pH by 0.1 to 0.3 units below the no-N control. The low floodwater pH indicated that ammonia volatilization was unimportant for all the N fertilization practices. Floodwater ammoniacal-N concentrations following application of urea or 16-20-0 were greater on this Sulfic Tropaquept than on an Andaqueptic Haplaquoll with near neutral pH and alkaline floodwater. The prolonged, high floodwater N concentrations on this Sulfic Tropaquept suggested that runoff loss of applied N might be a potentially serious problem when heavy rainfall or poor water control follow N fertilization. The unaccounted-for¹⁵N in the¹⁵N balances, which presumably represented gaseous N losses, ranged from 20 to 26% of the applied N and was unaffected by urea fertilization practice. Grain yield and N uptake were significantly increased with applied N, but grain yield was not significantly affected by urea fertilization practice. Yield was significantly lower (P = 0.05) for 16-20-0 than for urea; however, this difference in yield might be due to later application of P and hence delayed availability of P in the 16-20-0 treatment.     

The influence of rate and time of nitrate supply on nitrogen fixation and yield in pea (Pisum sativum L.)

The influence of nitrate N supply on dry matter production, N content and symbiotic nitrogen fixation in soil-grown pea (Pisum sativum L.) was studied in a pot experiment by means of¹⁵N fertilizer dilution. In pea receiving no fertilizer N symbiotic nitrogen fixation, soil and seed-borne N contributed with 82, 13 and 5% of total plant N, respectively. The supply of low rates of nitrate fertilizer at sowing (starter N) increased the vegetative dry matter production, but not the seed yield significantly. Nitrogen fixation was not significantly decreased by the lower rates of nitrate but higher rates supplied at sowing reduced the nitrogen fixation considerably. Applying nitrate N at the flat pod growth stage increased the yield of seed dry matter and N about 30% compared to pea receiving no nitrate fertilizer. Symbiotic nitrogen fixation was reduced only about 11%, compared with unfertilized pea, by the lowest rate of nitrate at this application time. The pea very efficiently took up and assimilated the nitrate N supplied. The average fertilizer N recovery was 82%. The later the N was supplied the more efficiently it was recovered. When nitrate was supplied at the flat pod growth stage 88% was recovered, and 90% of this N was located in the seeds.     

The effect of zinc fertilizer on take-all and the grain yield of wheat grown on zinc-deficient soils of the Esperance region,Western Australia

Wheat plants were grown in field experiments with five levels of zinc (Zn) fertilizer applied to plots in 1983. The plots were continuously cropped with wheat to allow the build up ofGaeumannomyces graminis var.tritici (Ggt). For experiments 1 and 2, there were high levels of Ggt in the second and third years while for experiment 3 there were high levels of Ggt incidence in the third and fourth year of continuous cropping. The Zn status of the wheat plants, grain yield, and the incidence and severity of take-all were measured for every experiment each year.The Zn-deficient wheat plants were more severely infected by Ggt. However, increasing the Zn supply beyond that required for maximum grain yield had no further effects on decreasing the severity of take-all. The Zn concentration in the youngest emerged blade (YEB) suggested that the Zn status of the wheat plant ranged from severely Zn-deficient through marginal deficiency to sufficiency.The Zn-deficient wheat plant was more susceptible to Ggt infection than Zn-adequate plants. The severity of take-all in the final year was still high in Zn-adequate plants, suggesting high levels of applied Zn (11.2 kg Zn/ha in 1983) had no fungistatic effect on Ggt.