Soil and crop monitoring in a processing tomato fertigation experiment in a reclaimed saline marsh soil in SW Spain using proximal and remote sensing.

Reclaimed saline marsh areas in SW Spain are characterized by a fragile balance in the rootzone between salt accumulation and leaching. Increasing climate variability and the introduction of new crops and irrigation methods can disrupt this balance, with undesirable environmental and economic consequences. In addition, the decreasing availability of irrigation water and the need to limit fertilizer use in areas vulnerable to nitrate contamination requires the implementation of more sustainable fertigation practices. A field experiment was set up in a commercial processing tomato field in the B-XII irrigation district (Lebrija, Seville) where four fertigation treatments (conventional and sustainable irrigation and fertilization) were compared in a random design with three replicates. Each elemental plot consisted of three tomato rows, each 250 m long and 1.5 m wide. Apparent electric conductivity (ECa) of each treatment was measured weekly using an electromagnetic induction sensor and multiespectral images were obtained on two dates using an UAV. ECa could be linked to the irrigation treatments and showed a strong within-treatment variability in accordance with the local soil characteristics and the depth of the underlying saline water table. The largest NDVI was observed for the sustainable irrigation and fertilization treatment, while the smallest NDVI corresponded to the sustainable fertilization and conventional irrigation treatment. Plants in the latter treatment presented chlorosis due to excessive accumulation of chloride and sodium in the leaves, as a result of root-zone salinization during the irrigation season, resulting in a strong decline in tomato yield (~60%) for this treatment. Overall, tomato yield showed a strong correlation with NDVI (R≈0.90). Our results suggest that more sustainable fertigation practices can be implemented in salinization-prone agricultural areas without increasing the risk of topsoil salinization or loss of crop productivity.

Acknowledgement

This work is funded by the Spanish State Agency for Research through grant PID2019-104136RR-C21/AEI/10.13039/501100011033, and by IFAPA/FEDER through grant AVA2019.018. Additionally, this work is also funded through PhD grant PRE2020-095133 by the Spanish State Agency for Research, and co-funded by the European Social Fund.