On-farm reduced irrigation and fertilizer doses, and arbuscular mycorrhizal fungal inoculation improve water productivity in tomato production

Viability of horticultural production requires high yields of high-value products, coupled with optimization of inputs. Rational fertilizer and water use are vital for the economic and environmental sustainability of vegetable production. Microbial resources are also used to increase yield, reduce inputs, and improve product quality. That includes arbuscular mycorrhizal fungi (AMF), symbionts associated with 80% of plant species, including many vegetable crops, such as tomato. To evaluate how AMF inoculation and reduced water and fertilizer affect tomato yield and quality, we carried out three independent experiments in commercial-production medium-technology (growth in soil, plastic cover, and no temperature control) greenhouses in Catalonia, Northern Spain. In the first experiment, AMF inoculation increased fruit number, total yield and improved fruit quality (soluble solids concentration or color) using lower fertilizer doses than those usually adopted on the farm. In a second assay, plants grew under three irrigation regimes: the farm usual regime, a managed-deficit regime (75% of the former), and an optimized dose using weather and plant-growth data. Deficit and optimized irrigation increased tomato yield and fruit size, but not fruit soluble solids concentration or color, and there was no effect of AMF inoculation. In the third experiment, fertigation was reduced by regulating irrigation doses according to soil moisture data. AM-inoculated plants sustained yield levels with 13% lower water and fertilizer rates. Reduced fertigation associated with AMF inoculation resulted in a 1.6% decrease in costs, which corresponds to at least six times the price of available commercial AMF inoculants. In all experiments, AMF inoculation was associated with increased water productivity, the ratio between product yield and the volume of irrigation water. Gains in input use efficiency, not only simple yield increase, should define commercial AMF inoculant use in vegetable production. We argue that researchers should estimate the financial incentive that AMF inoculation incurs so that farmers and inoculant producers have a base to test and adopt AMF inoculation technology.