An estimation of tomato transpiration for effective fertigation management system using integrated solar radiation and vapor pressure deficit

Tomatoes (cv. "Momotaro Fight") were grown in a bag culture with a drip irrigation system using coconut coir as a substrate. An efficient fertigation management system using integrated solar radiation and vapor pressure deficit (VPD) were conducted in order to confirm the efficiency of the system and to obtain the data of transpiration rate (E). With this system nutrients and water were supplied when the cumulative solar radiation (CSR) reached a value of 1 MJ m², setting the supply volume (per 1 plant^-1 MJ^-1 m²) was gradually increased depending on the growth stages. The E value of tomato was measured using a weighing lysimeter. The E data obtained from the V-100 treatment which was associated with the highest water and nitrate use efficiency, were used to perform linear regression equation for the estimation of E value relating either VPD and/or CSR. The linear regression equation of E value fitted moderately well with both VPD and CSR. Therefore, a more suitable fertigation system could be developed based on the estimation of the E value with VPD and CSR values. Moreover, the linear regression equation obtained could be applied for developing fertigation management system in tomato bag culture under wide range of greenhouse conditions.