Improvement of irrigation water productivity through water deficit and biostimulation in pepper under greenhouse conditions

The south-east of Spain faces a complex water scarcity scenario. Even though those regions have a high agricultural activity due to the advanced production system that has been developed. As it is important to optimize the use of water, from an economy, environmental and social point of view in these regions, it is needed to combine all available tools, including the technological and agnomical ones. Regulated deficit irrigation (RDI) techniques have been proved to be an efficient method of saving water in woody crops. Our hypothesis is that, as these RDI would cause a higher water stress in horticultural crops, that could be faced by biostimulation, as one of biostimulants claims is to improve the plant tolerance to abiotic stress, leading them to obtain a higher yield. This study aims to evaluate the effect of different strategies that combine the application of seaweed and microbials biostimulants with deficit irrigation programmes on the production parameters and soil quality in pepper (Capsicum annum sp.) under commercial greenhouse conditions.

With this aim two trials were carried out in commercial greenhouses (U & V), each one with two treatments:  i) irrigation according to Farmer criteria and ii) a combined treatment of RDI and the same biostimulation programme, that consisted of two application of Bacillus paralicheniformis after transplant via fertigation and four biweekly applications of Ascophillum nodosum extracts via fertigation and foliar spray. In each greenhouse, RDI was applied in different phenological stages,  from the onset of blooming to harvest in U trial or during the harvest in V trial.

The irrigation was reduced approximately 600 m³ ha^-1, implying a 12% savings respect to the Farmer irrigation schedule. The pepper yield had not been negatively affected, increasing the water productivity when RDI is combined with biostimulation. It is worth noting that when a water stress was applied, flowering and fruit setting seems to be promoted in biostimulated treatment, leading to a higher yield that non-biostimulated. Globally, the yield improvement has been due to a higher harvest of 1^st quality fruits.

This combined treatment has also improved the soil enzymatic activity in both greenhouses, suggesting that nutrients in the soil will become more available to plants when those are biostimulated.

Thus, the combined action of biostimulation under different strategies of irrigation reduction have been proved to be a useful strategy to improve agricultural sustainability, as it has increased the water productivity of the crop and the microbiological activity in the soil.