Plants get their carbon from the atmosphere – this process is called photosynthesis. Legumes, of which clover is one, get their nitrogen from the atmosphere, a process referred to as nitrogen fixation. Grasses do not fix nitrogen and hence are reliant on soil nitrogen, which comes from either free clover nitrogen or fertiliser nitrogen. Plants take up water and this is their source of hydrogen and oxygen. That is four out of the 10 taken care of.
New Zealand is fortunate that most of its soils have plenty of manganese, iron, zinc, copper and chloride. They do not need to be added to our soils to make plants grow, but some zinc is used to protect animals against facial eczema. Iron and chloride deficiencies are unknown in New Zealand, manganese deficiency has been induced by over-liming (pH > 6.8) and copper is sometimes required on peat soils. That leaves two unaccounted for.
There is heaps of calcium in our soils and for this reason calcium deficiency in pastures is unheard-of. The reason for this is that our soils are geologically young – they have not had the calcium weathered out of them. In any case many are of sedimentary origin and hence rich in calcium to begin with and we add lots of calcium inadvertently to our soils in lime (40% calcium) and super (20% calcium). So, only one left.
Boron is not required on clover-based pastures, only on brassica crops and where white clover is grown for seed.
Now you understand why our industry is focused mainly on delivering nitrogen, phosphorus, potassium and sulphur, and sometimes magnesium and molybdenum. That is where the nutrient action is in terms of the fertility of NZ soils. Other countries, and especially in the tropics, have very different priorities.
Some caveats are required. Calcium and magnesium deficiencies can occur in lactating cows but this is a consequence of hormonal imbalances, which occur particularly around calving time, and not necessarily due to low soil calcium and magnesium levels. Sodium is not an essential nutrient for pasture plants but it is required on a few crops like fodder beet and sometimes added to in fertiliser to get the pasture sodium levels above the critical level (> 0.1%) for lactating cows.
This occurs in NZ only in interior regions far from the sea where soil Na levels are not maintained by salt spray. For the same reason we add selenium and cobalt which are not essential plant nutrients but are required for animal health.
The so-called Albrecht soil testing system, with its emphasis on base saturation ratios, is in vogue at present in what I refer to as the anti-science brigade. If you are selling calcium-based products this system is a god-send, because invariably it will tell you the calcium-base saturation is lower than the ideal. Do yourself a favour and ignore this nonsense – it is pseudoscience.
One final thought. A plant can grow only as fast as the most limiting nutrient. Get all the soil nutrients into the respective optimal ranges to grow a healthy, vigorous clover-based pasture.
- For more information go to www.agknowledge.co.nz
NZ is fortunate that most of its soils have plenty of manganese, iron, zinc, copper and chloride.
