Arable Updates

No. 80 Maximising profit from nitrogen fertiliser

Fertiliser comprises 10-15% of the total cost of producing a typical maize crop. Thus optimising the amount of fertiliser applied to maize is important.

Key points

  • The rate of fertiliser that gives maximum profitability is usually much lower than the rate that gives maximum yield.
  • The level of soil nutrients can have a significant impact on the response of yield to fertiliser.
  • Without an accurate yield prediction, it is not possible to estimate the costs and benefits of a given management decision, such as fertiliser application.
  • Improved returns on N fertiliser ($) are possible if N fertiliser inputs are matched to maximise economic returns and not maize yield.

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No. 79 Effect of timing and placement of N fertiliser on maize yield

This study compared a range of timings and methods of fertiliser N placement, with a view to providing growers with a basis for making short term decisions about fertiliser application and longer term decisions about application equipment.

Key points

  • There was no significant effect of timing or placement of N fertiliser on maize grain yield, grain quality or crop biomass for a maize crop grown under average field conditions.
  • However, a single application does increase the risk of N losses to the environment through leaching, denitrification and volatilisation if weather conditions are adverse during the growing season.

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No. C216 Willow weed control in spring sown oats

This update outlines the results of a trial set up in a crop of oats near Gore to identify herbicides that provide good control of willow weed.

Key Points

  • A herbicide trial was set up in a crop of spring sown oats near Gore to investigate the control of willow weed following reports of growers having difficulty controlling this weed.
  • Saxon™ 3 l/ha (group O), Bromotril® 1.2 l/ha (Group C) and Trimec® 3.5 l/ha (Group O) gave complete control of willow weed.
  • Both Granstar® and Glean®, which belong to the sulfonylurea herbicide mode of action (group B), performed poorly on willow weed at this site.
  • It is possible that a biotype of willow weed with increased tolerance or resistance to group B herbicides has developed after many years of application of these herbicides.
  • Willow weed seed was collected from the trial site and will go through formal resistance assessment.
  • To slow the development of resistant weeds it is important to alternate herbicides from different modes of action (eg Group C and O) that are effective on the target weed species.

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No. C215 Foliar aphicide persistence on winter wheat

The aim of this field trial was to evaluate the persistence of selected insecticides (Karate Zeon®, Mavrik®, Pirimor®, Transform™, Eco-oil®, and Poncho®-treated seed) to a cereal aphid species, R. padi L., to provide growers with information on their residual activity against cereal aphids.

Key Points

  • A foliar aphicide persistence trial was set up in winter wheat sown in April 2017 at Plant & Food Research, Lincoln.
  • The trial tested aphicides from four modes of action: synthetic pyrethroids (Karate Zeon® and Mavrik®), carbamates (Pirimor®), sulfoxamines (TransformTM) and chloronicotinyl (the seed treatment Poncho®). It also tested Eco-oil®.
  • Poncho®-treated seed had residual activity to GS21 (32 days after sowing).
  • TransformTM at a full rate gave 8 to 14 days persistence, similar to previous trials.
  • Pirimor® gave 5 days persistence, similar to previous trials.
  • The synthetic pyrethroids have not given consistent residual activity. In previous spring trials their residual
  • activity ranged between 5 and 7 days. In previous winter trials when the aphids weren’t confined to the plant with clip cages residual activity had been long e.g. 25 days for the full rate of Karate Zeon®. The repellancy effect of synthetic pyrethroids may have contributed to this long activity. In this trial, when the aphids were confined to the plant, the observed residual activity has been reduced to a half or less than half the length of time compared to previous trials.
  • In addition to persistence, other factors need to be considered such as price, rotating modes of action to avoid resistance developing and choosing insecticides more compatible with beneficial insects (e.g. Pirimor® and TransformTM).

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No. 78 Nitrogen - Measure it and manage it: Year 1 results for maize growers

The industry agreed good management practice for nutrient management is to match the nutrient supply from the soil and fertiliser to the demand from the crop to reach its yield. To do this with a degree of confidence, farmers require reliable information and methods for working out how much fertiliser to apply to their crops. This three year programme of work focuses on nitrogen fertiliser decisions for maize, potato and leafy green growers. This summary is the maize component of the project.

Key points

  • The Quick Test Mass Balance approach is an effective method for informing in-season nitrogen (N) management decisions for maize growers.
  • Nitrate Quick Test strips can be used to estimate mineral N levels in the soil at any time during the crop’s growth. They may be used as a cost effective substitute for the mineral N test, particularly for top soil samples (0–30 cm depth), where nitrate-N is the predominant form of mineral N.
  • Quick Test estimates of soil mineral N levels can be used for fertiliser mass balance calculations to inform in-season N management decisions for the crop.
  • The mass balance calculation for a side-dressing decision is: N FertSD = [Crop NTotal – Crop NSD]
  • Soil Min NSD – Soil Org N mineralised. Information about the potential crop demand and the soil nitrogen supply is required.
  • The mass balance calculation can either verify the fertiliser plans for the crop are correct, or support less fertiliser being applied, e.g.at site 2 in this trial. It can also indicate that more fertiliser should be applied to reach the potential crop yield.

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