Abstract
The effects of lower nitrogen (N, 4 me·L−1 NO3-N) concentration on growth, fruit yield, and yellow-shoulder (YS) disorder of tomatoes (Solanum lycopersicum L.) were investigated at EC 0.9 dS·m−1 (N, 6 me·L−1 NO3-N) combined with potassium (K) supplementation. Tomatoes ‘CF Momotaro York’ were grown in extremely low-volume substrate (ELVS) combined with low-node-order pinching and high-density planting (LN&HD). An experiment with five nutrient solution treatments of Enshi formula nutrient solution at EC 0.6 and EC 0.9 dS·m−1, EC 0.6+KNO3 (in which 1 me·L−1 KNO3 was added to EC 0.6 dS·m−1), EC 0.6/0.9 (nutrient solution ranging from EC 0.6 to EC 0.9 during fruit enlargement and ripening stages) and EC 0.9+P+K (P and K concentrations increased to 4.6 and 5.8 me·L−1 in EC 0.9) was conducted. Tomatoes were grown in 250 mL pots filled with granular rock wool combined with LN&HD from Feb. 10 to May 29, 2012. The fertigation system of high frequency and small volume was based on integrated solar radiation level. Total yield and YS index at EC 0.6+KNO3 almost reached those at EC 0.9, but they were still significantly lower than those at EC 0.9+P+K. YS index decreased significantly when K concentration increased by 1 me·L−1 (2 to 3 me·L−1). The results suggest the possibility of increasing the yield when a lower-N (5.3 me·L−1) nutrient solution is applied in the ELVS culture system, if P and K concentrations are further modified to enhance the uptake. Shoot fresh weight at EC 0.6/0.9 was significantly lower than at EC 0.9, but there was no significant difference in total yield between EC 0.9 and EC 0.6/0.9. Total yield increased with increasing NO3-N uptake per plant (R2 = 0.98, P < 0.01) and YS incidence of fruit decreased with increasing K uptake per plant (R2 = 0.92, P < 0.05) during the entire growing period.
