P & K – Is now the time to take advantage of low prices and build up soil reserves?
With autumn crop establishment in peoples mind it’s a good time to think about P and K.
It is important to maintain the soil indices around the target levels of 2 or 2+ for K depending on soil type. This is the best way to maintain the soil’s ability to stay flexible and buffer the effects of prolonged adverse weather conditions. It’s also important not to overreact in periods of bad weather, remember phosphate and potash do not leach. Extreme weather will erode some soils, on certain clay soils releasing K into the available ‘pool’. Heavy rain can increase leaching of nitrates and sulphur and other mobile nutrients causing soils to acidify, so more likely to have an adverse effect on pH than indices levels. Not forgetting pH is a function of nutrient availability. Research has shown that waterlogged soils sometimes become less acidic whilst they are saturated through processes of soil chemistry but return to a level lower than before this event so soil testing and liming should be considered vital after periods of extreme weather.
It may seem obvious that applying more than maintenance in a dressing will build up indices levels, but the reality is less clear. For example, in clay soils, it is extremely difficult to build up P and K indices after depleting them, sometimes taking up to 10 years to return to target K levels. As a rough guide it is suggested that a total application rate to move P from Index 1 to 2 is 850kg per hectare TSP. Not a practical choice for most farmers but now may be the time to strongly consider using low P and K prices to begin the process of correcting indices back to target levels. The converse of this argument is potentially the interesting part. If it theoretically takes 400kg extra p2o5 to move up index, then the removal of this will have a similar effect which at an of take of 50-60kg/ha would potentially take 8 years.
The RB209 states ‘experimental evidence shows that applying the maintenance dressing of P and K fertilisers to soils at index 0 or 1, even with the suggested addition for build up, will rarely increase the yield of many arable crops to that achieved on index 2 soils given the maintenance dressing alone’. Maintaining correct P and K base levels is also the only way to ensure full efficiency from Nitrogen inputs. A simple calculation of previous year’s yield to understand rotational balances will also save time and money.
Phosphate and Potash markets have seen price falls over the last 12 months, nearing the lows of 2009 and 2010 for phosphate and 2016 for potash, primarily due to lack of recent demand. Many believe the world market price is on a cycle depending on commensurate crop prices. Along with cash flow, affordability is a critical indicator of demand. So, as drilling finishes and we move towards calculating P and K requirements for application a number of questions should be asked.
- When did I last do soil testing and can I access soil analyses from previous years?
- When did I last do a pH test?
- Look at rotational balances – now yield is known, can I calculate remaining soil P and K?
- Have I taken P and K holidays in the past few years?
- As product demand increases, will prices increase?
- Is now the time to take advantage of lower P and K prices to build up my soil indices to target levels?
The importance of Organic manures has been drilled into people over the last decade, and more people are relying on these alone to provide the necessary P and K to maintain soil indexes. This is an ideal strategy but it is important to remember that slurry and FYM vary from farm to farm, due to diet and ironically K status of the farm, low K indexes tend to produce organic manures with lower K as do diets with maize silage. So it is really important to get a slurry test to check that you are covering what you are taking off.
So key messages for autumn reseeds and cereal plantings are soil test and check the organic manures you are applying and change your fertiliser plan accordingly.
We have a full offering of Autumn Grade PK products and granular limes, ranging from standard products to bespoke soil conditioning products containing additional calcium, sulphur, magnesium and trace elements.
The Feedsweet range is a blend of Gafsa rock phosphate, Polysulphate and Muriate of Potash blended into 4 new grades with a high ratio of calcium, sulphur, magnesium and valuable trace elements. Elements that traditional water soluble PK’s cannot offer.