The application of conservation agriculture techniques to cereal crops in the semiarid zones of Navarre - 57% of the surface area given over to crop cultivation in Navarre, is most profitable for conventional agriculture and improves the quality of the soil, apart from contributing to the sustainability of the environment. This was the conclusion of the agricultural engineer, Mª José Imaz Gurruchaga in her PhD thesis recently defended at the Public University of Navarra.
The study was entitled, "Determination and selection of indicators of soil quality for the evaluation of systems in Conservation Agriculture in cereal crops in the semiarid zones of Navarre".
Greater retention of water
Conservation agriculture takes on board those farming systems that reduce or do away with tilling and soil preparation, apart from maintaining part of the surface of the soil covered with the stubble from the previous harvest. This reduction in tillage gives rise to a consolidation and restructurisation of the soil that positively affects its capacity to function.
In the no-till systems the presence of straw on the soil surface and the reduction in tillage create conditions of greater water runoff, reduction of losses through evaporation and increase in capacity of water retention available for the plants, giving rise to enhancement in the efficacy in the conservation of soil water. Moreover, this system also has a positive effect on the control of soil erosion, given that the soil is always covered by plant residue from the previous harvest and, thus, the impact of the rain on the soil is less.
Specifically, it should be pointed out that in the trials undertaken, the non-tillage system, followed by the minimum tillage (a superficial tillage to 15 centimetres depth without turnover), demonstrated a humidity content greater than that of traditional tillage - tillage to 30 centimetres depth and with turnover of soil.
Less cost and greater quality
Moreover, on reducing the tillage work, the costs of production are also cut, particularly the costs of fuel, without negatively affecting the average production of the crop. Between no-till and minimum tillage, the author holds that the minimum tillage system is of greater environmental interest, given that it does not require any additional application of herbicides.
It has also been shown that the reduction in tillage has contributed to an improvement in soil quality. In the trials undertaken, the researchers explain, there was an improvement observed in the physical and chemical properties of the soil and an enhancement in the stability of the surface soil aggregates was also noted. Likewise, the activity of the worm population increased, one of the main indicators of soil quality.
As regards the sustainability of the environment, it is precisely the systems for soil suggested by conservation tillage which are the most effective tools in this sphere, reducing, as it does, fuel consumption and favouring the capture of carbon in the soil due to the increase of organic material in its content.
Ten years of Conservation Agriculture
This study was carried out by comparing the efficacy of four tillage systems on dry region cereal agricultural soil, in the mid, semiarid, region of Navarre, over a period of ten years (1994 to 2004). The treatments studied were two systems of conservation tillage, minimum till and no-till, traditional tillage method, and treatment that combined no-till with burning off stubble.
This last technique was included in the trials because, apart from being common practice in the area, it was deemed suitable for problems of weed control, diseases and the management of crop residues.
With this research it was shown that not tilling the soil affects the quality of the soil more than burning off stubble. The burning off of stubble carried out on untilled soil mainly affected those aspects related to the quality of the organic material and, for now, it has not been seen to affect the physical properties of the soil or worm population activity.