What is “priming” and how does it affect your soil?

Priming is currently a hot topic as it affects whether the fertilizer you are using is effective. For instance, when you prime a pump, the water you add allows the pump to start pumping water. If there is not enough water, you just wasted the priming water.

This is exactly what happens in your soil. When the microbes in the soil are fed nutrients “primed”, by the plant or amendment, it wakes them up and they start growing. But, whether they can continue to grow depends on the continual supply of nutrients. If there is enough balanced organic matter in the soil, they are fine. If not, the microbes will work hard to harvest some of the stored carbon, nitrogen and phosphorus in the soil. And instead of storing carbon in the soil, their labors will produce CO2.

A key point is “balanced” nutrition available in the fresh organic matter which is most available to microbes. Like us, if microbes do not have access to one of the key nutrients, e.g. N, P, S, K, Mg, Mn, B, etc. they cannot thrive. Clive Kirby’s group in Australia has demonstrated that by balancing the ratio of key nutrients in fertilizer regimens to bring the ratio of fresh organic matter to a C:N:P:S ratio of 10,000:261:32:48 they increased yield and substantially increased the stored soil carbon.

Source: Coonan, E.C., Kirkby, C.A., Kirkegaard, J.A., Richardson, A., Amidy, M. and Strong, C., 2020. Microorganisms and nutrient stoichiometry as mediators of soil organic matter dynamics. NUTRIENT CYCLING IN AGROECOSYSTEMS, 117(3), pp.273-298.