The intensity of leaf green color can be an alternative to estimate the N concentration because of the relationship between chlorophyll level and N in leaf tissue. The objective of the work was to assess green index of the zoysiagrass from the digital imaging analysis and the use of chlorophyll meter to predict the nitrogen nutritional status in sewage sludge fertilized areas. The experiment was carried out on a commercial property of zoysiagrass, located in the county of Itapetininga, State of São Paulo. The experimental design was completely randomized, with five sewage sludge doses: 0, 10, 20, 30 and 40 Mg ha-1, on dry basis (equal to 0, 100, 200, 300 and 400 kg ha-¹) of N available and four replications. The N concentration and green hue intensity were evaluated by using chlorophyll meter (GHI) and by the digital image analysis (G, H and DGCI) at 45th, 105th and the 165th days after sewage sludge application. The intensity values were correlated with the N concentration in the leaf blade and with the soil cover rate determined in the same season. The application of sewage sludge doses increased the green rates and the N concentration in the Zoysia grass leaves. The N concentration leaf can help the nitrogen top-dressed application because it has high correlation with the soil cover rate. The hue (H) obtained with the digital image and green hue intensity (GHI) obtained with the chlorophyll meter are correlated with N concentration and with the soil cover rate and can serve as an index to assist in the recommendation of nitrogen fertilization.
Zoysia japonica Steud; digital image; chlorophyll meter; green color index
