More pasture the answer

 High-fertility grass/legume pasture is also an excellent quality feed. As Dr John Roche, principal scientist at DairyNZ has written, “high quality pasture is high in energy, has good quality protein relative to cow requirements, adequate amounts of fermentable and physically effective fibre and reasonable mineral and vitamin levels.”

Of course, depending on season and cow condition, there is a role to play for supplementary feed, i.e. when it becomes substitution feed – replacing pasture – and waste and risk creep into the system. So pasture should be prioritised in good times or in bad and good soil fertility is a key to stimulating and maintaining that pasture growth and quality. 

When it comes to deciding on how much of which fertiliser to put where, it pays to make an informed choice, knowing where you stand before figuring out the implications of any change. 

Withdrawals can potentially be made from a farm’s soil nutrient ‘bank’; when it comes to phosphate levels, you must consider all the essential nutrients, as well as soil pH, rather than purely P. It pays to soil test strategically. For example, if living with current Olsen P levels is being contemplated, not applying a product like potassic superphosphate could lead to potassium and/or sulphur deficiency which may have a marked effect on production. 

Your nutrient advisor should have the tools to evaluate the effect of withholding an application of P in respect of Olsen P levels and pasture productivity. If and when a change in fertiliser policy is being contemplated, in order to get the most effective use of your expenditure, soil testing all your paddocks will give you a much clearer picture of what nutrients are required in which paddocks. Invariably you will find paddocks which could have less of one or more nutrients applied this year without any loss in pasture production and quality. Conversely, there will be underperforming paddocks which will require more than maintenance fertiliser to get the best out of the pasture. 

Negatively impacting on next year’s production through inappropriate changes to their fertiliser programme could eventually deliver a double whammy if dairy farmers are scrambling to make up for lost ground this season. 

Putting every blade of pasture to optimum use means good utilisation practices, but also tracking pasture performance and reviewing residuals relentlessly. There are four ways to capture pasture performance data that can be married up with soil fertility data to give insight on soil nutrient needs: where to invest, where to maintain and potentially where to cut back.

Direct observation 

Walking the paddock with a qualified nutrient advisor is a valuable start to the fact gathering. Another pair of eyes can help scan for the evenness of pasture growth and colour, urine patch contrasts and the pasture’s recovery after grazing. 

Soil testing 

Howard de Klerk writing in the Southland Demonstration Farm’s October update said, “spending the money on all paddock sampling was adequately rewarded by efficient use of fertiliser.” Taking as many tests as possible on many carefully selected transects will highlight in-paddock variability which can lead to the right nutrients applied at the right rates to the paddocks that require them. 

Pasture quality testing 

A plant with more chlorophyll will reflect more near-infrared energy than an unhealthy plant. So analysing a plant’s spectrum of absorption and reflection in visible and in infrared wavelengths can provide information about its health and productivity. In its herbage analysis, ARL uses near-infrared spectroscopy to reveal the nutritional value of the pasture being grown. 

Pasture quantity testing 

Devices like a C-Dax pasture meter can capture dry matter data and highlight those areas that need more attention. The laser scanning tow-behind device takes 18,500 readings per 500m compared to the 250 of a rising plate meter. 

• Dr Ants Roberts is Ravensdown chief scientific officer.