Fertiliser application rate and mineral content of grass

_{It is advisable to have fresh grass analysed for mineral content, as well as analysing grass silage later in the year.}

The information below was provided to us by SRUC colleagues Mary Young and David Lawson and is particularly relevant just now given the hard choices farmers are making as a result of massive increase in fertiliser price.

SRUC’s Dr David Lawson reported interesting findings in a trial measuring the effect of nitrogen application and timing on the productivity and quality of a pure perennial ryegrass sward in Aberdeenshire. The data from 2017 to 2020 shows there is a positive correlation between fertiliser application rate and ryegrass mineral content. Contrary to the belief that increasing grass yield would therefore dilute the mineral content of the grass sward.

It is important to highlight these results are based on a ryegrass sward that does not contain clover or herbal leys. However, this information is particularly important this year where rates of fertiliser application may be reduced, which not only has implications on the yield but also the reduced mineral and trace element content of the grass.

The trials results from 2017 to 2020 are very similar, the graphs below are compiled from the 2020 data. The percentages show the percentage reduction in mineral content when the half rate of 60kg N/ha are applied compared to the full rate level of 120kg N/ha. Of particular note, the Mg content of grass was reduced by 34%, Ca content by 32%, P content by 20% and Cu content by 31%.

Major Minerals:

Trace Elements:

As a valuable source of minerals to livestock it would be advisable to have fresh grass analysed and later in the year to analyse grass silage for mineral content. This will allow for proactive decisions and provision of suitable mineral supplementation to be made if necessary to ensure the animals requirements for minerals are being met.

Posted by SRUC Veterinary Services on 16/03/2022