#44 - Oct 2020 - Garden Stuff - © - Sandy Lang - slang@xtra.co.nz
MINERAL NUTRITIONOctober/November: Mid, late spring. Everything’s growing so fast…!
Soil nutrients: Plants need three main soil nutrients – the ‘macronutrients’, nitrogen (N), phosphorous (P) and potassium (K). Plants must also have much smaller amounts of a host of other ‘micronutrients’.
Nutrient status: Eastbourne soils are sandy and their ability to retain soil nutrients is low. It’s difficult to maintain adequate levels of all soil nutrients. Specific mineral nutrient deficiencies are common here.
Nutrient loss: Along with a naturally low nutrient status, our soils also lose nutrients every time we remove plant material from the garden - as food or as green waste. They also lose nutrients every time it rains heavily or is overwatered. The percolating water washes dissolved soil nutrients deep down (leaching) to below the rootzone. If soil nutrients are deficient a plant grows slowly and is weak and disease prone. For healthy plant growth, soil nutrient levels must be continually topped up…
Nutrient deficiency: The leaves of a nutrient-deficient plant are often discoloured. Experts can identify some nutrient deficiencies by looking at the leaves - non-expert diagnosis is unreliable. Commercial growers do expensive leaf analyses to identify soil nutrient deficiencies. In the garden it’s easier to apply a general fertiliser containing the full range of macro- and micronutrients. This will fix any nutrient deficiencies. It doesn’t much matter if some of the nutrients added were not particularly deficient. Our soils are unlikely to be overly high in any of them.
Fertiliser application: With a low-retention soil, it’s best to apply fertilisers ‘little and often’ to keep plants fed and to minimise leaching.
Chemical vs organic fertilisers: The nutrients in an ‘organic’ fertiliser are the same as those in a ‘chemical’ fertiliser. Whatever the source, K is always K and P is always P etc. The difference is, an organic fertiliser is usually derived from plant/animal remains while a chemical fertiliser is mined from a mineral deposit (but these minerals deposits are often derived from ancient plant/animal remains).
The problem with chemical fertilisers: It’s not the use of chemical fertilisers that’s the problem with some intensive agricultural systems but the too-heavy use of chemical fertilisers – especially on light soils. For the home garden, organic fertilisers are usually more expensive than chemical ones and the amounts of nutrients they contain are often very variable. Quality control is difficult in a product derived from a variable biological source.___________________________________