Robin Boom Agronomic Advisory Services

It’s interesting the conversations one can have in a single day. I’ve just returned from a field day organised by the Auckland branch of the NZ Institute of Agricultural and Horticultural Science held on an organic dairy farm I’ve provided soil fertility advice on for more than two decades.

This particular client got interested in organics due to family health issues, which were attributed to using agricultural chemicals and for more than 30 years – and has taken a holistic approach to farming.

What was noticeable for all of the rural professionals present was the high clover component in the pastures, and soil test figures show relatively good fertility from the use of Reactive Phosphate Rock fertilisers along with sulphur, potassium, trace minerals, lime and organic chicken manure.

Initially, biodynamics was tried but this alone depleted soil fertility and long-term earthworm numbers declined. Now biodynamic preps are no longer used and earthworm numbers are starting to build up again.

High milk prices

At this field day there were Fonterra and DairyNZ staff as well as some members of corporate dairy groups considering organics on some of their farms with the attractive high prices currently being paid for organic milk.

Talking to one of these corporate dairy representatives, he informed me they’re currently applying about 180 kg/ha of nitrogen/ha on their upper North Island farms, which I thought was far too high. He considered it low compared to what their South Island farms get – two to three times this amount.

No wonder the country has environmental problems and the finger is being pointed at dairying. Next the Dairy NZ consultant entered our conversation and he too thought 180 kg/ha of N was quite the norm. I told them both I sometimes tell my clients off if they are using more than 100 kg/ha N. Conversely, I had one of my dairy farmer clients recently inform me that when he told his local Dairy NZ discussion group he was using only 60 kg/ha N the consulting officer told him off and said he should be using at least 150 kg/ha N to get the most out of his farm.

Not sustainable

Applying large amounts of nitrogen is not sustainable, is environmentally destructive, has deleterious effects on soil health and is economically questionable. There is no doubt that applying nitrogen can make the grass look deep green. But if there is a lack of sunshine, like there has been this last month with all of the rain, the grass is high in nitrates and crude protein and low in sugars and structural carbohydrates – and it comes straight out the back end of the cow as liquid faeces. Talking to one client whose cows were doing 2.2 kilograms of milksolids each back in early September and whose Milk Urea Nitrogen levels were about 16 at the time, after applying a whole lot of urea around the farm – at the advice of his consultant – has doubled his MUN levels to about 30. And the cows are only doing 1.8 kg/ms in early October, even though more grass is on offer.

There is a known direct correlation with MUN levels in the milk and the nitrogen concentration in urine, which is the main contribution of nitrogen getting into ground water and waterways generally.

Another problem with artificial nitrogen is it makes grasses more competitive, which can choke out clovers and can also make clovers “lazy” so they don’t fix their own nitrogen from the atmosphere.

Get clovers right

Cows also milk better and animals fatten better on clovers than they do grasses, so the fertiliser budget should focus on getting clovers right in pastures first which fix nitrogen for free. If you haven’t got much clover in your pastures, then something is likely to be out of balance in your soil or there is too much nitrogen being used.

This brings us back to the main reason this organic farm had a good clover sward making up at least 30 per cent of the pasture mix – a balanced soil and the fact no nitrogen had been used for more than two decades.

If you’re going to use nitrogen, the best time to actually apply it is late-spring going into summer, when plants want to go to seed and are growing rapidly.

Applying nitrogen then produces more leaf rather than stalk; and because plants are growing rapidly and soils are not saturated, more of it gets taken up by plants rather than being lost into the environment.

Also if there is a surplus of grass, paddocks can be shut up to make hay or silage. Ideally, effluent paddocks should be the ones used for silage – even though they may be close to the cowshed, as the surplus nutrients being applied to these from effluent can then be redistributed around the farm when the harvested supplements are being fed out.

It also saves on the fertiliser bill because there is no need for additional fertiliser to replace what is being harvested, since these paddocks usually have surplus nutrients to begin with.

ROBIN BOOM, CPAg, member of the Institute of Professional Soil Scientists. Phone him on 0274448764.