Fertile discussion

By: Steve McAulay

There are a lot of opinions about fertilizer requirements. Many people believe natural is good and artificial is bad. I am a simple person. When I put fertilizer on my garden the vegetables grow well and look better than store bought vegetables. When I don’t put any fertilizer on the vegetables, they are small, have funny colours and don’t look particularly appetizing. I put fertilizer on my garden.

Lifestyle block farmers frequently ask, “Should I be fertilizing my paddocks?” The simple answer is actually a question, “Do you run short of grass in August and September?” If the answer is “yes” then the next question I ask is, “Can you reduce the number of animals you are trying to feed?” Farming is a balance between supply and demand. If the supply of feed is low, can you reduce the demand? For example, by moving animals off the property or having fewer animals over winter.

Many lifestyle farmers do struggle to have enough grass to feed their animals in August and September, when the soil temperature is the lowest. Soil reactions and microbial growth is slowest when the ground is cold and when the ground is dry. This is one of the reasons south-facing land doesn’t grow as well as north-facing land. North-facing land receives more direct sunlight. When fertilizer is required, the first product to apply is normally lime, which counters the effects of aluminum. Aluminum is present at low levels in almost all soils in New Zealand. At low pH levels, the aluminium becomes more water soluble. Aluminium is toxic to plant roots. For best plant health, the soil pH should be greater than 5.6. A soil test has a usual accuracy of +/- 0.2 pH. Hence, usual recommendations are for a soil pH above 5.8.

When finances are tight, always manage soil pH first (with lime application) then add other fertilizers. In New Zealand, the main nutrients applied after lime are: nitrogen(N), phosphate (P), potassium (K) and sulphur (S). They are frequently recorded on fertilizer bags as N, P, K, S. The most frequently used fertilizers after lime are superphosphate 10 K and urea. Superphosphate 10K provides 7.2 per cent phosphate, 10 per cent potassium and 8.4 per cent sulphur. Urea is 46 per cent nitrogen. As with most things, quantity of fertilizer is the important factor – specifically the quantity of the elements applied. For example, applying 500 kg/ha superphosphate 10K will provide 36kg of phosphate per hectare. Recording the quantity of each element and the seasonal timing of the application will help determine fertilizer application success.

Thinking that you are doing well and can boast that you apply the right fertilizer doesn’t mean a lot. Knowing the amount of fertilizer applied is true fertilizer knowledge.

Stephen McAulay, CEO and head vet, Wellsford Vet Clinic


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