'Canopy management' and late nitrogen applications to improve yield of oilseed rape

Abstract

Previous HGCA-funded work demonstrated that oilseed rape yield is reduced by the development of an over-large canopy. This project further developed and tested Canopy Management principles that will help growers achieve an optimum sized canopy through the correct timing and rate of nitrogen (N) fertiliser. Canopy Management involves measuring the amount of N in the soil and crop in February (soil N supply - SNS) and then applying sufficient N to build an optimum sized canopy with a green area index of 3.5 units by flowering followed by variable amounts of late N applied between yellow bud and early flowering depending on yield potential.

When the SNS was moderate or high the first N application made to the Canopy Managed treatments was at the 2nd conventional split timing (start of stem extension, end March/early April). When the SNS was low a small proportion of N was applied at the 1st conventional split (end February/early March).

During the project, methods were developed to calculate what proportion of N must be applied early for crops with a small SNS. Experiments were set up in 2005/6, 2006/7 and 2007/8 at ADAS Boxworth, High Mowthorpe and Rosemaund. Each experiment included two varieties (Winner and 'low biomass' variety Castille), grown at seven N rates (0 to 360 kg/ha) applied at Conventional timings (50% in late Feb/early March and 50% in late March) and Canopy Management timings, with and without Folicur applied at green bud.

The project showed that delaying N through using Canopy Management principles increased yield by up to 0.36 t/ha in situations where the crop would have produced an over-large and lodging-prone canopy. The yield increases were associated with reduced stem growth leading to shorter plants and less lodging, and possibly increased seed set. Methods of employing Canopy Management were developed so that they are applicable for all types of crop, including low biomass varieties and crops with a small SNS.

The assumptions that underlie Canopy Management were validated within the study. Using the Canopy Management principles to calculate the N fertiliser requirement was shown to be accurate across sites and seasons, and more accurate than RB209 guidelines. The application of Folicur at green bud increased yield by up to 0.32 t/ha and resulted in average yield increases across the nine experiments of 0.15 t/ha for Winner and 0.10 t/ha for Castille, in the presence of minimal amounts of disease.

Using Canopy Managed N timings did not affect the size of the yield response to Folicur. Results from this project have been used to develop the 'N-Calc' fertiliser recommendation system run by Growhow UK Ltd and to help revise the current RB209 guidelines.