Wednesday, 17 December 2014

Pasture assessment the key to optimising nutrient investment


Dairy farmers searching for efficiencies in their operation know that home-grown, fully-utilised pasture has always been the most cost effective feed. 

Even before the current downturn, many farmers were not only looking at “output ratios” such as milk solids per cow, but also at “feed efficiency” ratios, such as the cost of producing a megajoule of metabolisable energy per kg of dry matter.

High-fertility grass/legume pasture is also an excellent quality feed. As Dr John Roche, Principal Scientist at Dairy NZ 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 along with reasonable mineral and vitamin levels.”

Of course, depending on season and cow condition, supplementary feed has a role to play. It’s when supplementary feed becomes substitution feed i.e., replacing pasture, that 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 definitely pays to make an informed choice. It’s all about 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 with potentially significant effects on production.

Your nutrient advisor should have the tools to evaluate what withholding an application of P might mean in terms 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 on the farm will give you a much clearer picture of what nutrients are required in which paddocks.

Invariably you will find that there will be numbers of paddocks that 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 that 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.

Dr Ants Roberts is Chief Scientific Officer at Ravensdown.

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 real 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 more than adequately rewarded by efficient use of fertiliser.” Taking as many tests as possible on multiple, carefully-selected transects will highlight between-paddock variability which can lead to the right nutrients applied at the right rates to the paddocks that require them. A laboratory like Ravensdown’s ARL can turn soil tests around quickly and make them available on an interactive map. If you’ve already got lots of soil test data, make sure you put it to use!

Pasture quality testing
A plant with more chlorophyll will absorb more near-infrared energy than an unhealthy plant. So analysing a plant’s spectrum of both 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 mineral composition also helps to fine tune nutrient requirements advice.

Pasture quantity testing
Devices like a C-Dax Pasture Meter can capture real 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. Whichever method you choose, frequent checking on growth will allow for a more accurate feed budgeting forecast, and help identify poorly performing pastures which, at best, may just need soil fertility correction or, at worst, have ‘run out’ and will need renewal.

We all know the dairy industry is cyclical, so putting your information to use and growing the same or more pasture will stand you in good stead when the inevitable bounce-back comes.​