Extinction coefficient and interception efficiency of the photosynthetic photon flux density in cherry tomato under levels of nitrogen in greenhouse conditions

Cherry tomato (Perinha Água Branca cultivar) was cultivated under organic management in greenhouse conditions set up in the municipality of Seropédica, Rio de Janeiro state, Southeastern Brazil. The crop was subjected to different nitrogen doses (N) ranging from 0 to 400% based on the reference value for the crop (100 kg ha-1) applied by means of dairy cattle wastewater. In order to estimate the extinction coefficient (k) and interception efficiency (Ԑint), weekly measurements of the photosynthetic photon flux density (PPFD) were performed below (PPFDb) and above the canopy (PPFDa) and the Leaf Area Index (LAI) was estimated. The extinction coefficient k for each treatment was obtained based on the model proposed by Monsi and Saeki. Ԑint was estimated by the quotient between PPFD absorbed by the canopy (PPFDabs = PPFDa – PPFDb) and PPFDa. Statistical tests were applied to k and Ԑint to evaluate the distribution of data (Kolmorogov-Smirnov) and their significance (Kruskal-Wallis), considering the treatments applied. No statistically significant differences were observed for k (p<0.05), which indicated canopy structure uniformity. The median k value was 0.792. Similar to k, Ԑint showed no statistically significant differences (p<0.05) between treatments; however, the highest interception efficiency was achieved by treatment with 300% N (Ԑint = 0.825), which coincided with the highest leaf area index and the lowest by treatment with 100% N (Ԑint = 0.521). The nitrogen did not interfere in the plant canopy architecture; however, it provided greater leaf area index to plants submitted to nitrogen doses two and three times above that recommended for the crop. Treatment with three times the recommended nitrogen dose reached in a shorter time interval the maximum efficiency value