Nitrogen Mineralization Kinetics as a Function of Tillage

Technical articles - National Center for Agroecology - Cost reduction

Does reduced tillage lead to a change in mineralization kinetics at the seasonal or annual scale in a plot? Or more practically, should I fertilize earlier in no-till (NT) to compensate for reduced mineralization?

Cover crops and nitrogen mineralization

It is known that tillage causes a slight mineralization peak. However, if a cover crop is established immediately after, the available nitrogen will be quickly absorbed. Indeed, newly established plants are at a physiological stage where they consume nitrogen. As can be seen here, in this trial in Belgium, where wheat was sown using Conservation tillage following a short intercrop with a previous pea. Establishing a cover crop destroyed on October 1st prevented the loss of 100 kg of nitrogen per hectare during winter.

Regrowth of oilseed rape is also a very good example of an effective cover crop for trapping nitrogen.

The nitrogen trapped in the cover crop will then be released in spring with soil warming. As the link between trapped nitrogen and cover crop biomass is proportional, it is therefore necessary to aim for maximum biomass if we want to limit nitrogen losses during winter.

Relationship between development and nitrogen in aerial parts. Source: CA Nord Pas de Calais.

So the more developed the cover crop, the more nitrogen will be trapped.

Mineralization kinetics

Regarding mineralization kinetics, we will consider two archetypes, wheat and maize. When tilling the soil for wheat in autumn, there is a slight mineralization peak that quickly subsides. If sowing in no-till, there will be no mineralization peak at sowing time. There will be no impact on crop development, as wheat nitrogen needs are low at this stage. Then, wheat nitrogen needs restart at tillering and reach a maximum at the 1 cm ear stage. At this time (February), soils are cold, and the tillage done the previous autumn no longer has an impact. As shown below, there is no difference in nitrogen residue between treatments (Feb. 04). This is why fertilization at the beginning of the cycle should not be changed for wheat whether using tillage or no-till.

Wheat-maize rotation. Boigneville 91. Source: K. Oorts et al. Soil & Tillage Research 94 (2007).

In this other example, conducted this time in Brittany, the observation is the same: there are no significant differences between tillage treatments on the overall nitrogen balance under wheat, between February and July 2015, in the zero nitrogen input treatment.

Nitrogen balance under wheat from February to July 2015, zero nitrogen control. Source: STBFN Project, 2021.

L-M: Plowing and mineral fertilization.

NT-M: No-till and mineral fertilization.

L-PM: Plowing and poultry manure.

NT-PM: No-till and poultry manure.

Spring crops

Regarding spring crops, a spring tillage warms the soil, which triggers mineralization. In a spring crop established in no-till or strip-till, there will therefore be a delay in mineralization early in the cycle due to lack of tillage. Below, treatments with tillage have higher nitrogen residues in June.

However, if we look at the overall balance at the crop scale, there is no difference, the early cycle delay being compensated later in the season.

That is why in NT or strip-till, for spring crops, it is absolutely necessary to localize fertilization at the starter to compensate for the lack of mineralization at crop start.