by Roger Martyn
Note : This article was written many years ago, when I was a dairy farm consultant in New Zealand. While Australia is not New Zealand, and many soils in Australia are sodic (although not very many in dairying) , the messages this article contains are just as pertinent to Australian soils as they are to New Zealand’s.
Some years ago, in New Zealand, I attended a Dairy Research field day held at Ruakura No2 Dairy, Hamilton, which included a stand on Autumn Fertilizer issues manned by soil scientists. On the accompanying display board was a list of useful and useless fertilizers. Included in the useless category was salt (sodium chloride). A MAF (Ministry of Agriculture and Fisheries) spokesman said they (MAF soil scientists) were willing to stick their necks out and make these claims. This raised more than one eyebrow among those who attended. The claim that salt is a useless fertilizer is certainly contrary to the findings of many farmers successfully using salt as a fertilizer additive and also contrary to the evidence of well respected researchers, ironically MAF included. Perhaps what they really mean by salt being a useless fertilizer is that it will not make dairy pastures produce any extra feed as measured in dry matter terms. Point taken. There appears to be no research evidence that applying salt will result in increased dry matter production although this says nothing about its improved palatability, utilisation and so on.
Lower Vet Bills
There is, however, overwhelming evidence, both in research and from farmer experience that including salt as a fertilizer additive can help decrease bloat, decrease spring metabolic problems and accompanying vet bills, improve pasture palatability and utilisation, decrease grass pulling (dislodgement) and all in all contribute to extra profit for the farmer.
Growing lots of grass is not necessarily all that difficult. The recipe is simple. Pour on the super, pour on the potash, pour on the urea, and re-sow your pastures every three years, as done at No. 2 Dairy. Sure, this will result is lots of dry matter production, at least initially, but enthusiasm soon wanes as pastures become clumpy, clovers start disappearing, stock are unsettled, spring eczema, grass staggers and bloat become endemic, and the only ones who seem to profit are your vet and the fertilizer company.
It is one thing is to grow grass. It is another to turn it into profit.
Important metabolic regulator
Salt is important. It plays a central role in almost every cell in the cow body and in regulating her blood, digestive and excretion processes.
Salt helps maintain a constant body temperature minimising winter cold stress and summer heat stress.
The requirements for salt of a lactating cow are surprisingly high. A well grown Frisian peaking at 25 litres per day requires the equivalent 45 grams of salt a day (18 grams of sodium) just to match what goes out in her milk. This can increase five fold if she suffers from mastitis. Allowing for other losses (urine and dung) this requirement increases closer to 65 grams of salt.
A healthy cow that has an adequate sodium level will display a 'dewy muzzle' just like this cow.
In pasture terms she needs to be eating pasture with a sodium content of around 0.18% (assuming 15kg dm feed intake and 90% uptake of sodium).
If the sodium levels are low in the pasture, she can utilise her body reserves, but for how long?
It is odds on that the pasture she's eating won't have optimum levels.
Of 250,00 pasture samples analysed at Ruakura over a 23 year period 67% showed less than optimal sodium levels for dairying.
A survey of Waikato New Zealand dairy farm pasture analysing 99 sites showed that 58% had less than optimal sodium levels. The same survey indicated that potassium levels were excessive for 40% of the sites.
There is no question that sodium can be raised in pasture by adding salt to a fertiliser programme. Again it is ironic that most of the above information comes from state funded sources through the likes Dr C. W. Holmes, emeritus lecturer in dairy production at Massey University; Dr N. D. Grace, author of ‘The Mineral Requirements of the Grazing Ruminant’ and DSIR researcher; and Dr Max. Turner another highly respected emeritus soil science lecturer of Massey University yet most contemporary fertiliser advisers and many dairy industry farm extension officers choose to ignore the evidence in favour of high potassium fertiliser inputs.
Cows well supplemented with mineralized salt tend to also tend to have glossy coats, a sure sign of health. Bothersome fly's also tend to be not attracted to such cows.
Success Stories
Wharepuhunga farmer Peter Horn substituted salt for potash in his spring fertilizer. He reports less pasture pulling this autumn, more even grazing of paddocks and he's sure the bloat is less severe this year. He thinks laying off the urea applications may have helped too.
Arapuni farmer Brian Eden had a new grass paddock the cows wouldn't graze.
"The grass was like wire and the stock would stand at the gate and ball at you if you went near them. I would have to move them by mid-day or they wouldn't eat anything."
He applied agricultural salt at a rate of 100 kg/ha and within 5 weeks the cows loved the pasture. The paddock hasn't looked back since.
Roto-o-rangi peatland farmer Gary Borland substituted salt for potash in his spring fertilizer.
"In spring the grass was so 'hard' it was getting stuck between the cows' teeth. Some were getting so bad that the roots of the teeth were starting to show on the gum. I had to clean the grass out when drenching there was so much. The grass is much softer now and this no longer occurs. . I stopped drenching for bloat by Christmas and this is the first Autumn I haven't had to drench.
Pastures are now being grazed more evenly too."
Te Awamutu farmer John Hine reports more even pasture grazing, less bloat, less summer grass presence and improved cow blood test results since adding salt and trace elements to his fertilizers beginning last autumn. "I used to be drenching for bloat twice a day during the autumn, now I'm only drenching once daily."