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Organic matter matters at SPot North Field Walk - 6 June

4 July 2019

There were more than 50 visitors to Strategic Potato (SPot) Farm North for the first field walk of the season at RJ & AE Godfrey’s Eastoft Grange Farm.

The growers and agronomists in attendance were introduced to three the trials and demonstrations running at the North Lincolnshire site this season.

The trials and demonstrations:

  • Irrigation
  • Pre-emergence weed control
  • Organic matter

Technical Report

Pre-emergence weed control

  • What: Pre-emergence weed control experiment. Joe Martin AHDB
  • Contractor: Eurofins Agrosciences. AHDB contact: Kathryn Hales
  • Water rate: 200l/ha, 4 replications
  • Date of planting: 15.4.19. Date of application: 2.05.19
  • Weeds: oilseed rape, charlock, knotgrass, bindweed and ivy leaved speedwell.
Treatment Description
1 Untreated control
2 Emerger 1.75l/ha
3 Shotput 0.5kg/ha + Praxim 2.5l/ha
4 Emerger 1.75l/ha + Shotput 0.5kg/ha
5 Emerger 1.75l/ha + Praxim 2.5l/ha
6 Emerger 1.75l/ha + Stomp Aqua 2.0 l/ha
7 Emerger 1.75l/ha + Gamit 0.15l/ha
8 Emerger 1.75l/ha + Praxim 2.5l/ha + Defy 3.0l/ha

The trial so far: Moderate weed levels present in untreated plots. Weed emergence was uniform across the trial. Conditions had been dry the previous week

Treatment 1: Some weed control provided by Emerger alone at 1.75l/ha compared to the untreated, but not sufficient to give commercially acceptable control. The groups felt that this product would be best in mix with other herbicides, based on what was observed at this site.

Treatment 2

Treatment 3

Treatment 4

Treatment 5

Treatment 6

Treatment 7

Treatment 8

Note: The pictures are only taken from one replicate and final results will provide the full story. Best treatments across the trial included Treatment 3 (Shotput + Praxim).

Many visitors on June 6th reported variable re-emergence weed control on their farms this year, in spite of using what they felt was a robust mix of actives. Several growers reported having used or being about to use the post-emergence herbicides Titus (rimsulfuron) or Basagran (bentazone). The AHDB herbicide trial faced the same strong weed challenge in dry conditions.

Irrigation  Dr Mark Stalham NIAB CUF

Tuber initiation was visible on a plant lifted today, 18 days after emergence. From this stage, 3mm across, the tuber is susceptible to Streptomyces scabies. Dr Stalham explained that the exudate which eases the path of the developing tuber is a perfect food for this pathogen, but also for competing beneficial microbes. Moisture from rain or irrigation helps the beneficial organisms to dominate.

Three treatments in the trial field:

  • single use drip tape down each row
  • rain gun
  • boom

In the very flat field, the drip tape run at 0.7 bar fills the 350m length and starts to drip in 4-5 minutes, providing 3.4mm water in 2 hours. Daily application is required for scab prevention in dry conditions.

Mark Stalham took what might be seen as a provocative approach, emphasising the drawbacks of drip irrigation in relation to overhead delivery. He asked the group “In the extreme situation of 19% relative humidity, temperature of 35oC and a 12 mph wind, what proportion of the water leaving a rain gun is lost to evaporation?” Members of the second group made suggestions of 10%, 25% and 50%. In fact, when calculated with help of catch can measurements, the loss is only 4%, about 1mm of a 25mm irrigation.

Since losses from overhead irrigation are not as bad as sometimes thought, the water saving advantage of drip tape appears less striking, while the disadvantages include higher cost, the difficulty of removing the drip take from the crop at the end of the season and waste plastic pipe to dispose of. As a rule of thumb, half of crop roots need to be exposed to irrigation for it to be effective. Where soil contains little clay or organic matter, drip tape must be laid down each crop row for the water to reach sufficient roots.

Some attendees commented that from their own experience they thought drip tape could be cost effective, for example on high-value crops of M.Piper for packing and Mark concurred.

IMAGE: Furrows still wet following 15mm rain gun irrigation on evening of 5.6.19

Above: Furrows still wet following 15mm rain gun irrigation on evening of 5.6.19

Mark also pointed to advantages of booms compared with rain guns. The photograph above shows water lost in furrows and unavailable to plants after rain gun application. Soil infiltration capacity was 8-10mm/hr while it had been applied at a rate of 15mm in 15 minutes (60 mm/hr). The 6mm/hr application rate from a boom would have infiltrated better, but a rain gun run at less than 12mm/hour would have left dry patches if wind conditions were adverse.

Organic Matter. David Clarke NIAB

The SPot demonstration is comparing half the field with added pig manure (34 t/ha) last autumn, with the other half that did not receive it. This is part of longer-term work comparing the effects of manure added at different stages in the rotation.

Organic matter matters! David Clarke told us about an experiment of OSR at Saxundham where the plots that had less organic amendment and therefore lower soil phosphate levels and suffered more severe pigeon damage than the plots receiving manure.

David explained that the organic matter content of the field we were looking at is 5.5%. This relatively high figure is partially explained by applications of pig manure over a long period in addition to crop residues from wheat and peas. He said that in research on land without benefit of manure, returning crop residues to the soil each year for 20 years had increased OM from 1.7% to 2.9%. Additional years led to no further increase.

In NIAB experiments at Morley three cultivation treatments; ploughing, deep non-inversion and shallow non-inversion affected the position of organic matter in the soil, but not total carbon content, after 14 years.

At the Morley site receiving regular additions of 35t/ha of green waste compost was applied for 4 years. Wheat yields showed a maximum yield response of 15%, and the benefit remained for at least 7 years after the final application.

When asked who was adding organic matter to their own land, several attendees said they are chopping and incorporating straw. One made the point that even in 2018 he’d stuck to this practice. Other forms of organic matter are hard to come by in this area. Some mentioned that poultry manure is no longer available because it goes to AD plants and the digestate is only viable to transport a short distance. One grower from near Doncaster uses both FYM and liquid digestate.

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