Are your cows getting enough phosphate?
7 April 2022
For healthy cows, it is important that the roughage contains sufficient nutrients. Too little phosphate, for example, can cause major problems. The condition of the soil and the nutrient content of the manure determine how much nutrients grass can absorb. And thus also how much ends up in the roughage. Analyses of fresh grass, soil and manure provide insight into the uptake and availability of essential nutrients.
'How a farmer lost many cows due to phosphorus deficiency'. Recently, this alarming headline appeared in the newspaper again. Karst Brolsma, researcher at Eurofins Agro, recognizes the problem: "A lack of nutrients does indeed lead to major health problems in cows. The solution is to ensure that the feed contains sufficient nutrients, in this case phosphorus. Whether that is through home grown roughage or whether it has to be brought in from outside the farm can be verified through analysis of soil, manure and grass."
If grass does not absorb enough phosphate, the roughage automatically contains too little phosphate. Often phosphate fixation is one of the underlying problems. The phosphate in the soil is then bound to other elements in the soil. On soils with a low pH there is fixation to iron (Fe) and on soils with a high pH to calcium (Ca). The phosphate is then in the soil, but the crop cannot access it.
For soils with a low pH, some of the phosphate can be made available to the crop by liming. In this way the pH in the soil is increased. The amount of available phosphate then increases.
However, on soils with a high pH, it is not possible to lower the pH. Other solutions must be sought here. The supply of sufficient phosphate is also a challenge. From a legislative point of view less can be supplied with animal manure. It is important to know what is in the manure that can still be used. Therefore carry out an analysis of the manure.
Then distribute the manure over the land as follows. On grasslands with a phosphate state 'low' you use more manure and on grasslands with a phosphate state 'high' you use less manure. In this way the supply of phosphate from the manure can be optimized.
If there are no major differences in phosphate status between plots, it is important to look at nitrogen supply prior to fertilization. Make groups with a difference of at least 50 kg of nitrogen supply from the soil. Then distribute the manure through this grouping.
Uptake by grass
Brolsma says: "The first cut is very important for the final quality of the roughage. In order to determine whether there is a problem with the phosphate absorption of the grass, it is important to have this in sight quickly. After all, the grass silage will only be analyzed a few weeks after ensiling. The sooner you have visibility of a shortage, the sooner you can take measures to optimize fertilization for the next cuts."
"A fresh grass analysis can help you quickly identify a possible deficit from the soil. By analyzing the grass before mowing, the fertilization for cut 2 can still be adjusted," he exclaims.