Abstract
Frost in the uplands of northeast India frequently damages maize, leading to poor yields or even complete crop failure. We studied the feasibility of using reflectance spectra from a handheld radiometer and a camera on board a drone at 80 m above the crop to assess physiological changes, differential responses of crop to nutrient managements (N, P, and NPK) and also predicted the likely losses of grain yield caused by one night’s frost damage in 90-day-old maize crop in Meghalaya, northeast India. A portable single-beam field spectroradiometer (model SVC-HR-1024) was used to measure radiation in the range of 350 to 2500 nm with varying bandwidth at 1 m above the crop. All measurements (both before and after frost) were made strictly between 11:00 and 13:00 h, when the sun was almost overhead. Similarly, a Parrot Sequoia multispectral camera sensing in four wavebands was mounted underneath a drone (DJI Matrix 600 model). We compared the measured spectra with those recorded on the same crop before the frost and also measured several biochemical constituents in the leaves on the two occasions for comparison. The frost damage increased the reflectance in the photosynthetically active visible and infrared regions with a strong peak at 2100 nm while it caused a sharp decline in the near-infrared (between 720 and 1350 nm) and shift in the red edge. It caused a decrease in the normalized difference vegetation index as measured by the radiometer from an average of 0.36 to 0.13 and a decrease from 0.5 to 0.31 as measured from the drone. The yield in frosted year was on average 870 kg ha − 1 less than in the previous frost-free year on the same plots. Frost injury reduced leaf pigments (chlorophyll and carotenoids), nitrogen, and grain yield by a greater magnitude in P-stressed and NPK-deficient maize crops over N-stressed and stress-free (with NPK) plants. Spectral reflectance and vegetation indices also varied significantly. We could also assess quantitatively the crop’s loss of photosynthetic potential from the hyperspectral reflectance measurements and from the low-flying drone. The latter technology should enable farmers to monitor and assess frost damage immediately and to predict the likely losses of yield.
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Claims 12
Claim · model-written summary
Frost increased reflectance in visible and infrared regions with a strong peak at 2100 nm.
- Treatment
- frost damagee0
- Outcome
- reflectance in the photosynthetically active visible and infrared regionse0
- Direction
- increasede0
- Value
- 2100 nme0
Zea maysNot reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The frost damage increased the reflectance in the photosynthetically active visible and infrared regions with a strong peak at 2100 nm”
t0“maize”
Claim · model-written summary
Frost sharply decreased near-infrared reflectance and shifted the red edge.
Not reportedTreatmentComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“it caused a sharp decline in the near-infrared (between 720 and 1350 nm) and shift in the red edge.”
t0“maize”
Claim · model-written summary
Radiometer NDVI decreased from 0.36 to 0.13 after frost.
- Outcome
- normalized difference vegetation index as measured by the radiometere0
- Direction
- decreasee0
- Value
- 0.36 to 0.13e0
Not reportedTreatmentComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“It caused a decrease in the normalized difference vegetation index as measured by the radiometer from an average of 0.36 to 0.13”
t0“maize”
Claim · model-written summary
Drone NDVI decreased from 0.5 to 0.31 after frost.
Not reportedTreatmentComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“a decrease from 0.5 to 0.31 as measured from the drone”
t0“maize”
Claim · model-written summary
Yield in the frosted year averaged 870 kg ha − 1 less than in the prior frost-free year.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The yield in frosted year was on average 870 kg ha − 1 less than in the previous frost-free year on the same plots.”
t0“maize”
Claim · model-written summary
Frost injury reduced leaf pigments more in P-stressed and NPK-deficient maize than in N-stressed and NPK-fed plants.
- Treatment
- Frost injurye0
- Outcome
- leaf pigments (chlorophyll and carotenoids)e0
- Direction
- reducede0
- Qualifier
- P-stressed and NPK-deficiente0
- Comparator
- N-stressed and stress-free (with NPK) plantse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Frost injury reduced leaf pigments (chlorophyll and carotenoids), nitrogen, and grain yield by a greater magnitude in P-stressed and NPK-deficient maize crops over N-stressed and stress-free (with NPK) plants.”
Claim · model-written summary
Frost injury reduced leaf nitrogen more in P-stressed and NPK-deficient maize.
- Treatment
- Frost injurye0
- Outcome
- nitrogene0
- Direction
- reducede0
- Comparator
- N-stressed and stress-free (with NPK) plantse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Frost injury reduced leaf pigments (chlorophyll and carotenoids), nitrogen, and grain yield by a greater magnitude in P-stressed and NPK-deficient maize crops over N-stressed and stress-free (with NPK) plants.”
Claim · model-written summary
Frost injury reduced grain yield more in P-stressed and NPK-deficient maize.
- Treatment
- Frost injurye0
- Outcome
- grain yielde0
- Direction
- reducede0
- Comparator
- N-stressed and stress-free (with NPK) plantse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Frost injury reduced leaf pigments (chlorophyll and carotenoids), nitrogen, and grain yield by a greater magnitude in P-stressed and NPK-deficient maize crops over N-stressed and stress-free (with NPK) plants.”
Claim · model-written summary
Spectral reflectance and vegetation indices varied significantly after frost.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Spectral reflectance and vegetation indices also varied significantly.”
t0“maize”
Claim · model-written summary
Hyperspectral reflectance measurements quantitatively assessed lost photosynthetic potential.
Not reportedValue
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“assess quantitatively the crop’s loss of photosynthetic potential from the hyperspectral reflectance measurements”
t0“maize”
Claim · model-written summary
Low-flying drone measurements quantitatively assessed lost photosynthetic potential.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“assess quantitatively the crop’s loss of photosynthetic potential from the hyperspectral reflectance measurements and from the low-flying drone.”
t0“maize”
Claim · model-written summary
The authors suggest drone monitoring to assess frost damage immediately and predict yield losses.
- Outcome
- monitor and assess frost damage immediately and to predict the likely losses of yielde0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The latter technology should enable farmers to monitor and assess frost damage immediately and to predict the likely losses of yield.”
t0“maize”
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