Best Use of Limited Supplies: Phosphate & Potash Fertilisers

Fine-tuning your P fertiliser decisions can use a soil specific approach to P management assessing the relationship between differing soils capacity to regulate your PK recommendations for your area (see the regional Technical Notes listed).
Grain P and K analyses after harvest of winter wheat can provide more accurate estimates of crop phosphate and potash offtakes than the typical values in FAS TN 715-718, 2020. This information also complements soil analyses for P and K. AHDB-funded research on P nutrition has shown that the critical level of grain P in winter wheat is 0.32%. Grain P contents repeatedly below this level indicate crop P uptake was deficient enough to reduce grain yield. If soil conditions are satisfactory but a field repeatedly shows grain P deficiency, available soil P should be increased for future crops. Grain samples must be representative of fields or areas from where routine soil analyses are taken.
Care should be taken to avoid building up crop-available phosphate above the target soil P Status. Recent research has shown that phosphate transfer from soil to surface water increases as soil P Status increases. Much of this transfer is due to the loss of crop-available phosphate through land runoff.
For cereal-based arable rotations, the target soil P Status is lower moderate (M-) on low and moderate P-fixing soils and upper-moderate (M+) on high P-fixing soils. The target soil P Status is M+ for rotations including potatoes and P responsive vegetable crops.
For cereal-based arable rotations, the target soil K Status is lower moderate (M-) on all soils and upper-moderate (M+) for rotations including potatoes and vegetable crops.
Adjustments to P and K fertiliser recommendations can be made to build up or run down to the new target soil PK Status by following FAS TN715-718s.

- PLANET Scotland, a free to download and use software tool designed for Scottish farmers and consultants, can be used to plan and manage nutrient use on individual fields.(http://planet4farmers.co.uk).