Don't let P and K indices fall

Some tillage farmers will already have been out in the fields over the past two weeks with compound fertiliser on winter barley and oilseed rape, in particular.

As weather allowed, it made sense to get some phosphorus (P) and potassium (K) out on crops and a small amount of nitrogen will keep those crops ticking over.

Early N on winter barley is questionable when it comes to yield benefits so it is important not to go too high with rates. Some oilseed rape crops with a low green leaf area index needed a kick of nitrogen to get them moving.

As fertiliser prices remain at high levels, it is hard to decide what to do in the fields. Last year, growers had bought fertiliser at lower prices in the autumn or had made decisions to cut back, but as grain prices increased, many rethought that strategy and pushed yield.

At that stage, though, some P and K rates had been cut and were not topped up. As hard as it is to pay for fertiliser, farmers should think long and hard before cutting P and K rates.

Of course, before we talk about any fertiliser, we must ensure that soil pH is correct, so that must be the first port of call. Soil pH, P and K are all essential in producing optimum yield and if they are not right, pushing nitrogen will only do so much.

Tillage farmers are generally good at keeping P and K at optimum levels and applying rates to maintain indices. Reducing rates and allowing indices to drop could prove more costly in the long run as it is harder to build P and K levels than it is to maintain them.

Tables 1 to 3 show recommended and compliant P and K levels for different crops. It shows the yields of the crops and the required adjustment to those rates with an increase or decrease in yield.

Organic manures are a brilliant way of helping to improve P and K levels over time on farms. They will not increase indices straight away, but when used as part of a long-term strategy they can play a really important role as they add organic matter to the soil and improve soil biological activity.

Straw incorporation is also a very good way of returning nutrients back to the soil. Once a crop is harvested and straw is sold the P and K in that straw is also sold. However, if you chopped straw last year those nutrients are not going to be immediately available so rates should not be cut dramatically until indices start to improve.