Do you ever feel there just aren’t enough hours in the day? How about enough days in the growing season for your home-grown tomatoes? The use of fertilizer may extend the growing season for tomato plants grown in a high-tunnel, a greenhouse like structure heated by solar radiation (Figure 1).
|High-tunnel (Photo: Jenna Meeks)|
The normalized differential vegetation index (NDVI), calculated using two wavelengths, red in the visible region and infrared in the invisible region, is used as a proxy for plant vigor. Therefore, NDVI is a tool to determine if fertilized tomato plants are healthier than unfertilized plants as the normal growing season comes to an end.
I studied the effect of four fertilizer treatments: a) Control (no fertilizer); b) 200 pounds of nitrogen as NPK fertilizer; c) a substitution of 75% of the N requirement with compost and; and d) a substitution of 25% of the N requirement with compost. Reflectance values were recorded from each plant four times with an Alta II Reflectance Spectrometer and the data were analyzed in Microsoft Excel.
The control plot displayed a lower NDVI than the fertilizer treatments, suggesting fertilized plants maintain their health for a longer period than unfertilized plants (Figure 2). The treatments with compost showed higher vigor than the control plot for half of the sampling dates, yet the 200lb N treatment was consistently higher than the control. These analyses are helpful to growers as they develop their fertilizer plan and crop rotations in their high-tunnels.