Assessment of soil health indicators in a regional strategy for climate change adaptation in agricultural land in Navarre (Spain).

Due to expected climate change effects, and with the aim of improving the resilience of the region of Navarra (N Spain), the Life Nadapta project has developed different studies on diverse knowledge fields. One of them is related to agriculture, more specifically to soil heath and the capability of improving its resilience through different agricultural managements.

These managements are conservation agriculture, organic amendments and crop rotation and the goal of this work was to assess the effect of these practices on three previously defined soil quality indicators (bulk density, water holding capacity and organic carbon storage).

To measure the effect of this practices over the agricultural soils of Navarra, previously a zonification process took place, considering the agroclimatic distribution and different bioregions. As result of this, the region of Navarra was split into 12 zones. Subsequently, for each zone, the more representative agricultural soil managements were selected in a network of more than 150 agricultural plots. On these, paired comparisons on plots with on the same soil unit and contrasting management were conducted to determine the effect of the selected management strategies on soil health.

Result of an extensive plot selection, 11 plots were chosen out of the 150 in the network to continue the study several years after the first assessment, comparing the effect of a conventional management with the adaptative ones on soil health indicators.

In addition, to account for all aspects of the sustainability of these managements in real life, the study took into consideration the economic yield and cost of each management strategy in these 11 plots.  

The groups of plots that showed significant differences in bulk density between adaptive and conventional management were those located in study zone 3 (semi-arid transition area). The plot under conservation agriculture management displayed higher values than the conventional one and the plot with organic amendments obtained a lower density.

Regarding carbon concentration, the same plot under conservation agriculture mentioned above performed worse than its conventional equivalent. On the other hand, in study area 1 (arid Mediterranean), the plot with organic amendments achieved a higher concentration than the conventional plot.

Finally, no differences were observed in any of the groups of plots studied, in terms of the water retention capacity indicator.

The economical balances showed that not all situations leading to improved soil quality resulted in a better economical behavior, which suggests that improving soil resilience may induce additional costs to producers.

Our results offer a first approximation of actual changes in agricultural fields when adaptive strategies are adopted at the regional level.