Nitrogen management in second wheats following strobilurin fungicide programmes


Cereals & Oilseeds
Project code:
01 April 2000 - 31 March 2002
AHDB Cereals & Oilseeds.
AHDB sector cost:
£103,757 from HGCA (project no. 2342).
Project leader:
J A KING ADAS Consulting Ltd., Boxworth Research Centre, Boxworth, Cambridgeshire, CB3 8NN



About this project


Strobilurins are a group of cereal crop fungicides, which may have a positive effect on crop yield beyond disease control. They increase yield by prolonging canopy duration, and thereby nitrogen uptake. It has been feared that this increased nitrogen offtake (10 - 40 kg ha-1) may reduce soil nitrogen reserves for following crops, and that extra nitrogen may have to be applied to compensate for this shortfall. This project followed the nitrogen dynamics of first and second year wheat crops on three soil types. The first year crops were treated with two types of strobilurin and a traditional fungicide, and also had three levels of nitrogen fertiliser (0, 160 & 320 kg ha-1 N) applied. The second year wheat was not fertilised, and had a uniform fungicide programme.

First year wheat:

Strobilurin fungicides produced a marginal yield enhancement above traditional fungicides (0.1 - 0.7 t ha-1) on clay loam and silty clay loam soils.

The yield enhancement was largely due to an increase in grain size.

No increase in nitrogen offtake was recorded at any site due to strobilurin use.

Mineral nitrogen levels in the soil after harvest, were not depleted after strobilurin use relative to traditional fungicides at any site.

Excessive nitrogen fertiliser application above the economic optimum, left large quantities of nitrogen in the soil after harvest, but did not enhance yields.

Second year wheat:

Excessive rainfall of twice the long-term average during the establishment phase led to higher than normal leaching and poor crop establishment on clay loam and silty clay loam soils.

Soil mineral nitrogen in the soil during the spring was not reduced by the preceding use of strobilurins.

The excess nitrogen left in the soil by high applications of fertiliser in the preceding year, had largely been leached from all the soils, but left an enhanced residue on clay loam and silty clay loams.

Excess nitrogen from the application of large amounts of fertiliser nitrogen applied in the first year produced enhanced yields (0.5 - 1.5 t ha-1), due to a similar enhancement of soil nitrogen supply.

The incorporation of straw reduced this enhancement by immobilising soil nitrogen.

There was no reduction of soil nitrogen supply or yield, due to strobilurin use in the first year.

No change in the management of crop nitrogen nutrition in second wheats can be recommended as necessary for crops following those treated with strobilurin fungicides. However, the excessive use of nitrogen fertilisers above the economic optimum, conveys no benefit in its year of use and only marginal benefit in the following year, but does contribute to an environmentally damaging leachate to waterways, and should be avoided.