Limiting the Impact of Harvesting and Optimizing Straw Management
Harvesting is a key link in the success of future sowings and the agricultural system in general: the preparation for the next crop starts in the combine harvester. In CA, harvesting is the first step of no-till farming.
Control traffic in the field as much as possible
Ideally, for a good soil structure, half of the volume is occupied by porosity. The pressure exerted by machinery passes in the fields creates a phenomenon called compaction, which corresponds to the reduction of this porosity volume. This directly affects the infiltration capacity of water and air, the ease of root penetration and exploration in the soil, as well as the functioning of biological activity.
To reduce the compacted surface area in the field, one can consider:
- Keeping trucks out of the field;
- Trying to unload while stopped at the edge of the field rather than on the move;
- Not turning in the middle of the field;
- The transfer vehicle must follow the same tracks as the combine harvester;
- Establishing a transport plan for the refueler/trailers and sticking to it. In this context, Controlled Traffic Farming is an interesting approach (see below).
Reduce soil pressure during operations
Surface compaction (<10 cm), accentuated by successive machinery passes in the fields, is all the more present when the tire is narrow and the pressure exerted is high. Deep compaction does not increase with successive passes but rather depends on soil moisture at the time of passage and the total weight of the machine: the heavier the weight, the deeper the compaction in the soil.
Visually, there is a tendency to want to make only one pass to reduce the presence of ruts on the surface. However, in terms of impact on soil structure, it may be wiser to make several passes with a lighter load, for example by avoiding filling the hopper and/or the refueler to their maximum capacity, because deep compaction is more difficult to correct than surface compaction.
Regarding tires, wide radial tires at low pressure allow better weight distribution and reduce soil stress, especially under wet conditions. Indeed, a radial tire has a wider and flatter footprint that cushions better than a bias-ply tire.
Also, central tire inflation is a technology that allows quick adjustment of tire pressure depending on the farming operation to be performed, on the road or in the fields. Used wisely, it reduces soil pressure and compaction. However, this option remains costly and must be well mastered.
Controlled Traffic Farming: to reduce the compacted surface
From a certain tool width (>6 meters), Controlled Traffic Farming (CTF) can be considered. Used on a large scale since the late 1990s in Australia, this technique limits the compacted area caused by machinery passes.
The idea is to define permanent traffic lanes in the fields using wide working widths and narrow tires to minimize the machine traffic area. It appears that CTF reduces soil compaction to only 15% of the surface, thus potentially less overall yield loss related to this issue.
This technique requires having tools with widths that are multiples of each other (4.5m/9m/18m or 3m/6m/12m). Changing the entire equipment fleet to implement CTF across all crops would represent a prohibitively high cost at once. Therefore, it requires a global reflection upstream, to be implemented gradually as equipment is renewed.
Keep straw on the soil to feed biological activity and improve structural stability
Crop residues are considered not as green waste but rather as key elements of farm productivity.
Straw is an eco-fuel for soil microfauna and flora. The degradation and mineralization processes feed a whole chain of organisms whose result is the improvement of soil structural stability thanks to the production of glomalin ("soil glue") which allows aggregation and organization of soil particles.
Once the straw is digested, lignin accumulates in the soil and contributes to humification (accumulation of stable organic matter), which has longer-term physical soil properties.
Manage straw according to equipment constraints: disc seeder or tine seeder
The cutting height of the straw and the ability to distribute and chop residues influence the subsequent process when straw is not removed and one wishes to direct seed a cover crop or a crop into the straw.
Disc seeders provide better seed-soil contact in the absence of lodged straw, or if the straw is standing, or if the straw is dry and cuts well. Thus, if equipped with a disc seeder, it is preferable to cut the straw as high as possible to avoid too many residues on the soil. The ideal is the stripper header, which removes the ears while leaving almost all the straw above the soil. A stripper header costs more than a normal cutter bar but allows better work rate because not all the straw passes through the machine.
Conversely, coarser chopping is a good alternative if equipped with a tine seeder or if soil work is planned post-harvest with tools that tend to clog. Coarse chopping can be considered if the soil has good biological activity.
Collect fine straw: an interesting lever for weed control
Fine straw consists of plant residues rejected by the combine harvester during grain cleaning at harvest (wheat, barley, oilseed rape). They are composed of straw pieces, grain husks, and weed seeds.
The primary benefit of this technique is to avoid returning weed seeds to the soil and thus reduce weed pressure over time.
A trial conducted by Arvalis from 2014 to 2018 demonstrated a significant effect of this practice on weed pressure. This trial was conducted on a no-till plot with a high presence of ryegrass resistant (>40 ryegrass/m2 at harvest) and studied a modality "fine straw collected and exported" versus "fine straw spread in the field". The first year, the technique allowed recovery of 70% of ryegrass seeds that had not fallen to the ground before harvest. Little effect was observed on weed cover in the short term due to the seed bank already present in the soil. However, a reduction in ryegrass pressure of about 40% was observed the following year and a 20% yield increase after 3 years, all other things being equal. Visible effects are therefore more medium to long term.
Establish cover crops to stabilize soil structure and improve porosity
Surface compaction (<20 cm) can be corrected by shallow tillage, unlike deep compaction (>20-30 cm) which cannot be mechanically corrected. The presence of roots in the soil and the action of earthworms can recreate porosity if present long enough in the field, but this takes more time.
Moreover, the porosity created by soil biology is the most resistant to pressure. Macropores created by plowing are poorly connected and poorly resist hazards and machinery pressure. Conversely, the microporosity favored by conservation practices is more resilient and facilitates root exploration.
Sources
7 key points for harvesting in a living soil approach, AgroLeague
