Soilless USDA-organic cultivation of tomato with ‘Natural nitrogen’ : a comparison study between ‘Natural nitrogen’ and organic nitrogen

In a USDA-organic soilless cultivation of tomato organic nitrogen is used as N fertiliser, which needs to be converted to crop available nitrogen by microorganisms around the plant roots. VitalFluid developed a technology that produces nitrogen fertilisers in a natural way in a reactor, using only air, water and electricity (‘Natural nitrogen’; HNO3). Implementation of this nutrient source in a USDA organic soilless nutrient solution is investigated in a cultivation trial. A comparison is made between this ‘natural nitrogen’ nutrient solution and a standard USDA organic nutrient solution (reference). The trial has shown that ‘Natural nitrogen’ can be implemented in a nutrient solution and has advantages over organic nitrogen sources. In the reference treatment, the microbial conversion of organic N had a slow start, so that NaNO3 needed to be applied to have enough readily available nitrogen for the crop to grow. This made it impossible to recirculate drain water in the reference treatment due to increased sodium levels (less K available), whereas the treatment with ‘Natural nitrogen’ could recirculate all drain water. Product quality and productivity of the crop were good in the ‘Natural nitrogen’ treatment, but due to the difficult start of the reference could not be compared to this reference treatment. It is also shown that ‘Natural nitrogen’ as source of N in USDA organic cultivation opens the way to adopting a closed-looped irrigation system. The technology can therefore enlarge the resource use efficiency (RUE) of such a system.