Fertiliser following first cut

Published 24 April 15

The application of nutrient following first cut needs to be a priority on a grassland farm during the week following cutting. Which nutrient to use depends on the availability of slurry and how much to apply depends on the next use for the crop, says Chris Coxon, from the Farm Consultancy Group.

One consistent recommendation is the use of sulphur, as it is required for effective uptake of nitrogen in the plant. An application of 40kg per cut of silage is now standard and deficiencies in grazing pastures can also show from mid-season onwards, meaning that even purely grazed fields will benefit from at least one 40kg application of sulphur per season.

Where the field is to be used for grazing, an application of around 40kg Nitrogen along with a similar rate of sulphur will set the field up to re-enter a grazing rotation. 

The use of slurry, ideally through a trailing shoe or injector to limit plant contamination, is best used for fields that are destined for a second cut. This should be used in conjunction with bagged fertiliser to ensure that the correct amount of nutrient is used. The ratio of nitrogen:phosphorus in slurry is 3:1, whereas the ratio in the crop is 7:1. Therefore, an application of slurry should be ‘topped up’ with an application from a bag.  

The balancing of slurry use should also involve the use of soil testing. For soils that have an index of two or greater, the total amount of phosphorus and/or potash should be accounted for. Soils with an index below two can be balanced by accounting for the available proportion of nutrients, which are 50% of the total phosphate and 90% of the total potash.

For a dairy farm with soil indices of two for phosphorus and two and above for potash, and an annual nitrogen requirement of 280kg nitrogen/ha, a typical recommendation for second cut is highlighted in the table below (Using RB209 data for a 7,500 litre yield, 2.2t concentrate/cow/yr, 2.2 LU/ha).

 

Crop Requirement

Nutrient from 40m3/ha Slurry

4% dry matter

Bagged Fertiliser

Total

Available

Nitrogen

98

84

34 (40% av.)

60

Phosphorus

25

36

36

0

Potassium

90

112

112

0

Sulphur

40

Maintenance only amount in slurry

40

There should be a three to four day gap between slurry and bagged fertiliser applications to limit any denitrification from the interaction with the moisture in slurry, nutrient and bagged fertiliser.

Getting the correct nutrient balance requires careful consideration. As there is no such thing as an ‘average recommendation’, there is good value in using soil tests and slurry analysis alongside a FACTS qualified advisor to ensure nutrient use is balanced.