Yellowing of wheat may be attributed due to many reasons. Dr O. P. Chaudhary, Head of Dept of Soil Science of Punjab Agricultural University reveal that following may be the possible reasons for the yellowing of wheat crop,
Manganese deficiency
Oxygen deficiency in root zone
Sulphur deficiency
1. Manganese deficiency:
Manganese deficiency generally appears in light soils under intensive cropping especially in rice-wheat rotation. Wheat and barseem crop show manganese deficiency symptoms when grown on soils having less than 3.5 kg available manganese per acre.
The wheat crop gives yellowish appearance after first irrigation. The symptoms appear on the middle leaves as interveinal chlorosis with light greyish yellow to pinkish brown or buff coloured specks of variable size.
The manganese deficiency can be corrected by spraying 0.5% solution of manganese sulphate (1 kg manganese sulphate in 200 litres of water per acre). Generally three to four sprays are required. Give spray at weekly interval on sunny day. Manganese sulphate should be sprayed only as its soil application is not profitable.
2. Oxygen deficiency in root zone:
In heavy soils, which have lower infiltration rate, water does not percolate below root zone after heavy irrigation or rain. This results in oxygen deficiency in the root zone. The roots are not able to work properly resulting in yellowing of crop. All the plants show yellowing of leaves from tips towards base.
In such conditions, remove the water from field and on field capacity, broadcast small quantity of urea for recovery of crop.
3. Sulphur deficiency:
Wheat crop suffers from sulphur deficiency when sown in sandy soils. The deficiency is more severe when the winter rains continue for a long time in the early growth period.
The symptoms first appear on the younger leaves with fading of the normal green colour. The topmost leaves become light yellow except for the tip, while the lower leaves retain green colour for a longer time.
Apply 100 kg of gypsum per acre to meet the sulphur requirement of the crop. Gypsum is best and cheapest source for supplying sulphur to crops.
Source: http://web.pau.edu
