Base Saturation Explained

Under our current system of soil fertility, we are being encouraged to under-fertilise. This state has existed for many years, but the degree of under fertilising is getting worse. Applying so called maintenance levels of nutrients is not even ensuring soil fertility is static; it is declining.

Base saturation is simply the percentage of exchangeable cations. Cations are the positively charged soil fertility elements. Base saturation is used to identify and measure the % of each cation to determine the soils’ available relative mineral makeup.

Total Exchange Capacity is the sum of the total exchangeable cations. A light soil (eg. Volcanic) having a smaller sum than heavy, alluvial silt loam.

The balance of cations determines soil structure, nutrient holding capacity, and fertiliser requirement for optimum production. Economic decisions can then easily be made to prioritise fertiliser applications.

Some cations are: calcium, magnesium, potassium, sodium, manganese, cobalt, copper, iron, zinc, hydrogen, and ammonium.

What we try to achieve (according to a Perry Agricultural Lab test), is calcium to be about 68%, magnesium 10-12%, potassium 2-5%, sodium 0.5-3%, hydrogen 10-15%, and other bases to be about 5%. Don’t try to fit these numbers around another test; it won’t work.

If the cation balance is close to this ideal, we will get good soil structure, moisture movement and retention, drainage, and maximum crop and pasture production and quality. All elements work together synergistically without antagonism, with pH being ideally constructed. Pasture and crop palatability and consequently, animal performance will all excel.


When calcium is present in the correct amount with other cations, the soil is at its most productive and efficient state. If calcium is deficient other cations, eg. Potassium will dominate the herbage to the detriment of animal health. If Ca is in excess, soil will drain and dry out faster. Phosphorus, trace elements and, magnesium availability will be low. Crops and pastures may show clinical symptoms of magnesium, iron, manganese and zinc deficiency. An application of ferrous sulphate will help.


Magnesium excess is not common in NZ. However, too much or too little in the soil results in too little Mg in the plant. Nitrogen efficiency is also affected, taking more N to achieve the same result. Soils stick to machinery when wet and set hard when dry. They take more horse power to work. It is far more common to find Mg deficiency in the soil, particularly as a result of over liming. Dolomite is the best material to build Magnesium; Dunite (serpentine) and mag oxide do not achieve the same results as they release the magnesium too slowly.


If potassium dominates, pasture palatability will be poor. Stock will require salt to compensate or metabolic problems will develop. Leaf carbohydrate can also break down, leading to lower yields. High K suppresses manganese, cobalt and magnesium. Potassium causes the most angst among farmers who are reluctant to apply it. The dilemma they have is high potassium in the herbage, while at the same time it is low in the soil. Most farmers are used to potassium chloride; however potassium sulphate should be used instead. Low soil potassium leads to lower pasture production. Keep calcium, magnesium soil levels up, and high plant potassium will not be such an issue. Some areas of NSW have very high potassium, but growers following this system manage to grow high yielding crops by getting Ca, Mg and Na to the correct levels. The soil under those crops is as hard as concrete.


Sodium percentage must always be lower than potassium. We find in a surprising number of cases, it is the other way around. That situation leads to excess sodium uptake. Plant cell walls can then burst on hot days, leading to dehydration and plant death. Perhaps that situation arises if farmers neglect the potassium, but apply sodium to raise pasture palatability. That is attacking the problem from the wrong end and will never solve it. Always try to solve a problem by removing the cause, not by removing symptoms. If K and Na together exceed 10%, or if Na is higher than K, manganese uptake will be blocked.


The above four cations influence pH. The closer they are to balance, the closer the pH will be to the optimum, being what it should be. Say that is 6.4; however, a 6.4 pH may be obtained by cations out of balance. For this reason, never use fertiliser to change pH. Only add it to change the proportion of the nutrients. pH should be the result of your fertiliser programme, not the cause of it.

Why use the Base Saturation percentages?

They give a logical explanation of your soil.

They give a total blue print of your soil.

They allow you to solve problems.

Farmers can relate data results to both good and problem areas.

No prior knowledge of nutrient levels in the soil is required.

The principles apply to all soils, plants and animals.

They give outstanding yields and quality of both plants and animals.

Practical considerations

In the short term, balancing the BS can be an expensive exercise. The alternative is to put on fertiliser to get your crop or pasture through the season. Remember, chemical agriculture is a self-serving, input-driven system. You are advised to apply an unbalanced fertiliser to an unbalanced soil to sustain a state of imbalance, which will then require constant chemical intervention. After 20 years of doing that, the chances are you will be no better of in year 20, than you were in year one. Many farmers are complaining they are worse off.

Balancing will require extra fertiliser. For some, the way to approach that is do a portion of the farm at a time. Hill farmers need to look at their flats first. Other farmers need to consider their silage paddocks, crop paddocks or parts of the property not doing so well. Over time your farm performance will increase, while eventually, your fertiliser applications will decrease. The point at which the fertiliser spend will decrease, depends on how long it takes to reach that balanced plateau. Once there, it is plain sailing down the other side.

The system we use at Kiwi Fertiliser is proven all over the world. This system has produced a world record yield of wheat in Germany; best quantity and quality wheat in NZ; 37-42t+/ha maize silage in USA; best quality and quantity raspberries; best quality and quantity bananas in Guatemala and South Africa; the best performing horse stables in South Africa; 20t+/ha of Lucerne all over the world, and growers being paid US$19/kg for their high yielding grapes by wineries in California, to name just a few successes.






Want real fertility results on your farm? Contact us today and request a soil audit.

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