Using Deep Convolutional Neural Networks for Image-Based Diagnosis of Nutrient Deficiencies in Rice

Table 2

Symptoms of nutrient deficiencies in rice plants throughout the growing period.

Class	Typical symptoms
Full	Leaves are green, generally with no mottling or spots.
−N	First appear in the lower leaves of the main stem and then gradually develop in the upper part. Leaves turn from green to yellow starting at the tip and extending along the midrib to the base of the leaf in a Λ shape until the whole leaf is chlorotic and yellow.
−P	First appear in the lower leaves of the main stem and then gradually develop in the upper part. Lower leaves are dark green, and then old leaves become yellow. In severe cases, the lower leaves are longitudinally curled with cyan or brown spots.
−K	First appear in old leaves and then gradually extend to new leaves, leaf tips, and leaf stems. Basal leaves gradually turn yellow or yellowish brown from the tip, along the edge, to the base of the leaf. Reddish brown or dark brown rust spots of varying sizes emerge. In severe cases, spots form plaques and spots appear on the sheath. Later, the tip of the leaf gradually turns red and brown, and the discoloration gradually spreads from the lower leaves to the upper leaves.
−Ca	Present on new and upper leaves. The tips of the fresh leaves turn white, curl, and shrink. In particularly severe cases, the growth point is necrotic. The upper leaf tip and leaf margin are yellow.
−Mg	First appear in the lower, old leaves, which become chlorotic, while the veins remain green with clear yellow-green stripes. Discoloration starts at the leaf tips and then extends to the middle and rear parts.
−S	First appear in young leaves, which turn yellow. In severe cases, old leaves turn yellow and even white. New leaves are green and yellow, and their tips are scorched. There are also water-soaked round brown spots.
−Mn	Manifest in middle and upper leaves, which become chlorotic and yellowish. The veins remain green, causing a great color difference between them and the rest of the leaves. Gray or white spots appear in severe cases.
−Fe	Appear only in new leaves, while old leaves remain healthy. Young leaves are chlorotic, yellow, and white, but the veins stay green.
−Zn	Appear in both new and old leaves. The bases of fresh leaves become chlorotic and white. Irregular brown spots appear on both sides of the middle and lower leaves. In severe cases, the brown spots extend to the leaf sheaths, which turn red and brown from the tip of the leaves, generally appearing from the lower leaves to the upper leaves.
−Si	Appear on lower leaves as brown spots.