P & K – Is now the time to take advantage of low prices and build up soil reserves?
We recently saw the release of the annual Soil Nutrient Status Summary 2012 – 2013. The report from NRM shows average P, K and Mg indices collated from soils sampled throughout the year and trends from the last 19 years. The results show clearly that despite 18 months of extreme weather, soils tested have held up better than expected. There is clear evidence that quantities applied have gradually declined over the years while trends in mean soil P, K and Mg have generally remained static. This implies that farmers are doing the right thing by trying to maintain soils at target indices. The problem we see with reports like this is that there is no such thing as an ‘average’ farm, a large data set tends to hide the extremes. Although encouraging to see that generally there has been no real effect of the poor weather, it is important to ensure that your unit is following the trend.
The term P and K ‘holiday’ has been used over the past few years to describe the practice of not applying nutrients to save money, a tactic which potentially runs down indices. In years when prices exceeded £500 per tonne for both P and K products it could be argued there was little choice. It may be time to rethink this strategy in a period of lower input costs.
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 over react 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 significant price falls over the last 12 months, nearing the lows of 2009 and 2010, 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?