Nitrogen Use Efficiency

NITROGEN USE EFFICIENCY AND SULPHUR

Worldwide nitrogen usage efficiency (NUE) for cereal production is approximately 33%. RB 209 gives figures for the UK of 55-70%.

As N fertiliser prices and environmental concerns both continue to increase, farmers must look at ways of increasing the utilisation of the fertiliser they apply.Plant breeders are already looking for varieties, which are more efficient at utilising nutrients, but the basic metabolic processes by which plants utilise nutrients must be taken into account. The uptake and assimilation of sulphur and nitrogen are strongly interrelated and dependent upon each other (1)

Sulphur is a constituent of the nitrate reductase enzyme, which is necessary for the conversion of nitrate to amino acids in plants. Low nitrate reductase activity depresses soluble protein levels while raising nitrate concentrations in plants. Sulphur deficiency leads to a decrease in chlorophyll, inhibits protein synthesis and may result in the accumulation of starch within the plant. Proteins formed in the plant tend to have low sulphur contents and are therefore of lower nutritional quality.

CEREALS

Ohio State University found that yields of maize achieved by 133kgN + S were higher than those where 233kg N was applied. N P K Mg and S were all increased in the maize grain, indicating that application of S with the N fertiliser promoted uptake of N and other major plant nutrients.

For milling wheat where high protein levels are required adequate levels of S are essential to utilise fully the nitrogen applied.

OSR

When S is deficient high levels of nitrate accumulate. This can inhibit seed formation in sensitive crops such as oilseed rape

In France NUE figures of 36-53% were achieved and oilseed rape was found to be less efficient at utilising both N and S than cereals.

GRASS

Sulphur fertiliser reduced the leaching of zinc, copper, iron and molybdate from the soil solution when applied to pasture (2)

In sulphur deficient grass only 44% of the nitrogen was protein N as compared to over 80% in non- sulphur deficient grass (3)

On a sandy loam site nitrate leaching was reduced by 72% in one year and by 58% in a second year where 15kg S per cut was applied with high (450kg N/ha/yr) nitrogen and by 10% and 5% where low N (200kgN/ha/year) was applied At high N levels peak concentration of nitrate-N in the leachate was reduced from 27.3 mg N/l to 9.3mg N/l (4)

Recommendations

Apply 30-60kg S per hectare or a ratio of 6-7N to 1 S. Ideally apply at least 50-100% of this over the winter period as elemental S so the crop has sulphur available when the yield characteristics are determined. The elemental S can form part of a programme with further S added in the sulphate form with spring N applications

Cereals

Grassland

Apply 15kg S after each cut.

For elemental S to convert to sulphate within the season of application particle size must be less than 150 microns. SulFer 95 is formed from micronised sulphur with 100% of the particles <75 microns

1. 1 Brunhold Regulatory interactions between sulphate and nitrate assimilation, Sulfur nutrition and Sulfur assimilation in Higher plants 1993

1. Phillips and Chiy Effects of applying sodium and sulphur fertilisers on the concentrations of elements in water leached from permanent pasture J Sci food agric 82 806-815

1. Bolton, Nowakowski and Lazarus Sulphur-nitrogen interaction effects on the yield and composition of the protein N, nonprotein N and soluble carbohydrates in perennial ryegrass

1. Brown, Scholefield, Jewkes, Preedy Wadge, Butler Effect of sulphur application on the efficiency of N use in two contrasting grassland soils

J agric Sci 2000 135 131-138

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