The residual effects of strobilurin fungicides on soil nitrogen for the following crop.

Abstract

This project asks the question ' Do strobilurin fungicides increase the depletion of soil nitrogen, and hence increase the need for nitrogen on the following crop?'

Season one (1998):-

Increasing inputs of nitrogen increased disease severity in untreated crops,
All fungicide treatments gave good disease control with yield responses of between 2.8 - 7.7 t/ha depending on nitrogen input,
The application of two strobilurin fungicide programmes gave a maximum yield response of 1.4 t/ha over the triazole treatment,
Crop nitrogen offtake increased in the two strobilurin programmes by 10.91 - 39.38 kg N/ha compared to the triazole programme, depending on nitrogen input.
The Following Season (1999):-

Nitrogen inputs and fungicide treatments in the 1998 experiment resulted in differences in Soil Nitrogen Supply (SNS) to the 1999 crop,
SNS for the 1999 crop was greatest following low yields in the 1998 crop due to a high level of disease, which resulted in low nitrogen offtake,
SNS following treatment with the two strobilurin programmes was generally lower than when crops were treated with the triazole programme,
Yield, specific weight and grain nitrogen were significantly reduced in the Amistar + Opus treatment compared to the triazole treatment.
Yield loss of up to £100/ha (grain @ £60/t) occurred following the application of a strobilurin programme to the previous years crop.
Conclusions:-

Strobilurins generally increase yield and hence nitrogen offtake,
As a consequence, SNS may be reduced for the following crop,
Differences in SNS are likely to vary with soil type and season,
Continued use of strobilurins with no adjustment in nitrogen use may affect future yields and grain quality.
Guidelines need to be established for appropriate nitrogen management following the use of strobilurin fungicides.