Before analyzing the results obtained from the timely monitoring of soil moisture, carried out rigorously during time intervals characterized by prolonged absence of rain, it is preferable to clarify its meaning and its link with the quantities of irrigation water.
The soil moisture is nothing more than the amount of water contained in the soil compared to the dry sample and is expressed as a percentage based on the weight of the soil (% by weight) or its volume (% by volume)
The maximum water content that a saturated soil is able to retain with capillary force without the phenomenon of percolation occurring is defined as field water capacity (C.I.C.). However, this water is not totally available to the plant, as the roots are unable to absorb the so-called unavailable water from the micropores. The difference between field capacity and unavailable water appears to be the water capacity of the useful field or useful reserve (RU), corresponding to the maximum amount of water available in the soil for the plant (variable depending on the soil and crop type). In order to avoid water stress for the plant, it would be advisable to irrigate exactly when the easily usable reserve (RFU = 0.4 ÷ 0.6 RU) runs out. Therefore, the decision of the most appropriate time to irrigate and the amount of water needed to be supplied is mainly based on the measurement of soil moisture in order to determine the water needs of the plant..By using the B.R.F. (Bois Rameal Fragmenté, or fresh twigs wood chips) in agriculture the aim is to increase soil protection, reduce the quantities of irrigation water and the resilience of the soil to superficial erosion phenomena and therefore to hydrogeological instability.
Below are some summary considerations relating to soil moisture data, with and without the B.R.F. technique, detected during measurement campaigns carried out on the land of a farm that is the principal of the ATS Progetto RESTORE. These data were acquired during time intervals characterized by prolonged absence of rain and thanks to the use of mobile instrumentation whose technical characteristics are reported in the monitoring sheets in the download section. The total absence of rain is essential to analyze the actual variation in soil moisture influenced only by the amount of irrigation water administered, in order to be able to compare the moisture trend over time of the portions of land with and without branches. In this regard, it should be noted that during the first measurement campaign (period 03.07.2020 – 10.07.2020), carried out on a portion of land cultivated with vegetables, the same amount of water was administered (5.5 l / plant to 48 hour intervals) both to plants grown on the area without branches and to those subjected to experimentation with the BRF technique. The following figure shows the temporal trend of the humidity detected, with an hourly frequency in the range 9:30 – 18:30, on both soils and it is clearly observed that the humidity in the portion of land covered by the chips of fresh twigs tends to grow if subjected to watering every other day. In the area without branches, however, subjected to the same amount of irrigation, however, the humidity always tends to more or less the same average value.
These results lead to an observation, namely that the branch manages to retain water while keeping the soil moist and that by subjecting it to the same irrigation of the soil without branching it tends to increase this humidity rate until it tends to the water capacity of the field of the soil itself.
Following these results, a second experimental measurement campaign was launched aimed at demonstrating the possibility of temporally distancing the irrigation operations on the land covered with twigs. To do this, on the same experimental site on which the first measurement campaign was carried out, the portion of land without BRF continued to be irrigated every other day while the area with the branches was not subjected to any irrigation for the whole interval 12.07.2020 – 17.07.2020. Obviously at the beginning of this second measurement campaign, following the irrigation operations carried out during the previous campaign, the soil with twigs has a high humidity rate which, as shown in the graph in the following figure, tends to decrease over time up to equal, after 5 consecutive days in the absence of irrigation, the values of the soil without branches and subjected to irrigation every 48 hours.
It is demonstrated, with a simple application case, that thanks to the use of the BRF technique it is possible to limit irrigation operations either by spacing them further over time or by simply administering a smaller amount of water than is required by cultivated land without branches.