Abstract
This research aimed to examine the effect of soil improvement based on leonardite on the intensity of photosynthesis and the lycopene content of tomatoes. Seven landraces of Hungarian and Slovakian origin were tested at two sites (Site-1, Site-2) under field conditions in the temperate continental climate of Central Europe. The treatments: (i) NPK nutrition (43.5:30:30 kg/ha NPK), and (ii) HUMAC Agro (HA), with the same nutrition and a soil-applied humic preparation from HUMAC Agro at a dose of 1,500.00 kg/ha. The lycopene content averaged 285.94 mg/kg and ranged from 6.18 to 658.54 mg/kg. The content was mainly influenced by the landraces (F-ratio 70,856.00, P-value 0.00), followed by the treatments (F-ratio 20,189.00, P-value 0.00), then by the sites (F-ratio 16,291.00, P-value 0.00), and finally by the replications (F-ratio 17.62, P-value 0.00). Lycopene orders, by: (i) land-races ‘Cegléd’ < ‘Zemplínsky’ < ‘Máriapócs’ < ‘Fadd’ < ‘Tolna’ ≤ ‘Mátrafüredi’ < ‘Gyöngyös’ (10.83 < 181.47 < 233.85 < 329.36 < 411.93 ≤ 413.293 < 420.85 mg/kg); (ii) treatments HA < NPK (254.96 < 316.92 mg/kg); and (iii) Site-2 < Site-1 (258.11 < 313.77 mg/kg). A phenomenon of harmonising effect of the humic amendment was observed, as the lycopene content changed from the extreme values to the medium values at both sites. Photosynthetic rate (PR) was monitored on Site-1 under two sequences: (i) TS (sequence temperature 20.3 – 41.7°C at constant FAR of 608 mmol/m2/s) and (ii) LS (sequence light/photosynthetically active radiation, FAR 0 – 1,304.00 mmol/m2/s at constant temperature 38.2°C). In both sequences, the higher PR was found in NPK (30.753 and 12.589 mmol/m2/s; LS vs. TS) compared to HA (22.347 and 9.271 mmol/m2/s). This indicates a climatic anti-stress effect of the humic treatment, which is probably related to the better-known effect of humic amendments on plant root improvement.