Arable News

  • Written by: Farmers Guide
  • Posted:

Potash use decline creates crop concern

Thosegrowers who continue to ignore the potash status of their soils could beplacing greater pressure on the nitrogen they are about to apply.


Thatsthe view of Frontier fertiliser manager, Chris Tye, who suggests that whiletheres been great effort taken to get a soils physical structure right, itsfertility is perhaps being compromised.


Hesays that fertiliser statistics for 2012 from the British Survey ofFertiliser Practice, just released by the AIC show that mean use of potashacross arable and grassland stands at a paltry 23kg K2O/ha.


Thatsanother drop on the previous year and is a third lower than the level of potashfertiliser applied ten years ago. 


PAAGanalysis reports also show us that 32% of all arable soils and 43% of grasslandfields based on a mean of soils sampled tested nationally over the last fiveyears – are now deficient in potash.


And, our own analysis data compiled by precisionfarming and nutrient mapping experts SOYL, confirms that the potash status inUK soils is far from ideal, with the number of those with soils in Indices 0 and1 rose again in 2013.


Comingat a time when nitrogen use is fairly static, this suggests that UK farmers arein danger of creating nutrient imbalances in their crops, he says.


MrTye points out that nitrogen use efficiency can only be maintained if potassiumin plants is at optimum levels and the ratios, based on current use, suggestotherwise.


Growersshould also be concerned about the potential loss of potash this winter, hesays.  While cereal and oilseed rape establishmenthas generally been strong and growth vigorous over the mild winter, plants willhave taken up less than a sixth of their total demand, and this will rapidly increasewith the onset of spring growth.


Withthe unprecedented winter rains weve experienced and a record January rainfallfigure, potash, which is normally effectively held in soils, is likely to have beenredistributed deeper in the soil profile, particularly on lighter soils.


ChrisTye points out that while potash prices have strengthened in recent weeks, theyremain at low levels compared to where they have been in recent years and currentlyrepresent good value set against commodity prices, particularly for oilseedrape.


Forthose that took a potash holiday when prices spiked, his message is simple; itis time to replenish the soil bank to ensure sustainable yields going forward.  Six years ago it took around 6kg grain topay for a kg of potash but today it is closer to 3kg.


Whilethere are signs that some growers are realising the need to back better K-useon their crops, and blenders are reporting strong order books through February,farmers who havent ordered already do need to move quickly to get supplies ingood time.


Theindustry could struggle to satisfy orders with delivery also likely to bedifficult over a narrowing logistical period when demand for nitrogen is alsoat a peak, says Mr Tye.


JerryMcHoul of fertiliser supplier, K+S UK & Eire says that growers need to be remindedthat if nitrogen is the fuel and phosphorus the key in the ignition, potash definitelyrepresents the oil in the engine.


Notonly does potash keep nutrients, sugars and fluids pumping around the plant, italso affords a protective role with positive effects on reducing lodging risk,disease susceptibility, drought and both high and low temperature stress.


Withoutsufficient potash, a plant cannot take up and hold onto adequate supplies ofwater or other nutrients, and will suffer both heat and drought stress whichwill curtail yield and also crop quality. 


Ithas a particularly close relationship with nitrogen because when taken up as anegatively charged nitrate form, a positively charged nutrient must match it andfor most crops this is potassium, says Mr McHoul.


Studiesat Rothamsted have shown that the N use efficiency is 79% at K index 2, but just49% in soils at K index 0.  This meansthat in our most seriously K-depleted soils that only half of all applied N isutilised, representing a serious financial and environmental loss.


MrMcHoul says that growers should be aiming on rebuilding the potash status oftheir soils and targeting index 2 as the standard for most arable crops andgrassland, but going even further for high value crops such as vegetables andfruits.


Healso points out that potash use also needs to be balanced alongside that ofmagnesium.  The PAAG surveys show that overone-sixth of the UK arable area is Mg index 1.0 or less that means that largeareas of oilseed rape and of cereals could also be underperforming due to lackof magnesium.


Inour extensive six-year trial programme, applications of magnesium, on these lowindex sites, have increased mean oilseed rape yields by 0.21t/ha, so growers doneed to check soil status for this macronutrient as well.


Wherefarmers have had nutrient holidays theres no better reference point to startwith than a detailed nutrient map.  It isonly through targeted fertiliser application, backed by soil analysis, thatgrowers can raise indices and then maintain them at levels that support highcrop productivity, he suggests.


  • Written by: Farmers Guide
  • Posted:
Prev Story:Focus on robust fungicide use this springNext Story:Beet management in focus at BBRO event