Salt as a Fertilizer - Useful or Useless?
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 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 feed.
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, increase pasture palatability and utilisation, lessen grass pulling and all in all contribute to extra profit for the farmer.
To grow lots of grass is not necessarily 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.
Salt is important. It plays a central role in almost every cell in the cow body 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 Friesian 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 more recent survey of Waikato dairy farm pasture analyses showed over 99 sites that 58% had less than optimum sodium levels present. 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 the fertilizer programmes.
Again it is ironic that most of the above information comes from government sources like Dr C. W. Holmes, New Zealand’s top dairy lecturer at Massey University; Dr N. D. Grace, author of ‘The Mineral Requirements of the Grazing Ruminant’, and DSIR researcher; and Dr M. Turner of Massey University.
Cows well supplemented with mineralized salt tend to also tend to have glossy coats, a sure sign of health. Flies tend to be much less of a problem for such cows.
Salt and Bloat
Dr Max Turner kicked this off in the early 1980's when investigating the relationship of sodium levels and bloat control.
He initially did this at Massey on trial plots and later repeated them in the Manawatu, Southern Hawkes Bay and Taranaki in farm paddock situations. More recent Ruakura work confirms much of Dr Turners work.
Dr Turner showed that a direct relationship existed between soil and plant sodium levels, that plant uptake of sodium was very similar to potassium and that potassium has a very real antagonistic effect on soil and plant levels.
He also showed that salt did not affect pasture production.
Dr Turner has also suggested a relationship exists between bloat and the potassium and sodium ratio. His earlier work suggested the optimum ratio of potassium to sodium in herbage be less than 20 to 1. Subsequent work suggested the optimum appears to be within the narrower range of 5:1 to 10:1.
Of the same Waikato survey mentioned above, only 16% were in the ideal 5:1 to 10:1 ratio range; 41% were in the 10:1 to 20:1 range and 43% over the 20:1 ratio range with the highest being at a 58:1 ratio.
It is worth mentioning that nitrogen as well as potassium fertilizers can widen this gap.
However none of the trial work done appears to attempt to quantify factors such as pasture palatability, clover imbalance where potassium levels are high, decreased pasture pulling, improved cow temperament or even improved per cow production.
Are these issues important or not?
There are many instances of farmers benefiting immensely from using salt as a fertilizer additive.
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."
There are many other instances out there. Salt is not the only player. Lime, trace elements and RPR fertilizers are playing their part too.
Should dairy farmers be questioning how fertilizer research is being driven?
In 1986 Dr Turner commented "What you are seeing is the way the system is stacked in favour of potash" But his research programme which had lapsed because of an apparent lack of support, had resumed "because the salt orders have started to come in."
By the way, that same display board listed magnesium, zinc and boron as useless fertilizers too, and Ruakura veterinarian Roger Ellison wrote in the December Dairying Today that copper was not effective when applied as a fertilizer! ( - a note to the uninitiated; magnesium, zinc and boron and copper are indeed very important fertilisers where required).
Footnote: Time has moved on, and there is a greater acceptance now that some of the minor and trace elements such as boron, copper and zinc might indeed be important fertilisers. Central to deciding if these fertiliser elements are important is what criteria is used to determine their importance. For example, if the requirement is determined simply by plant response as measured by dry matter production, some of these elements like Sodium in this article may not be considered as important. But this does not acknowledge the nutrient health value for the animal that consumes the plant, (or in turn, the benefit to the consumer of what that animal produces) and how do you measure that? Likewise, should the fertiliser criteria include the nutrient requirements of soil organisms as well of those of the plants growing within the soil? How can this be measured and is it even important? Increasingly these questions are being asked and debated, as they should. As usual, it is often the most academically qualified that seems the quickest to dismiss such thinking and the most reluctant to investigate apparent successes. For example see Bucolic Beauty article.