Zinc-deficient paddy soils: the crop suffers, and so do the people who eat it.
Zinc deficiency is one of the most widespread micronutrient problems in flooded paddy soils. Flooding raises the pH of acid soils and changes soil chemistry in ways that can make zinc less available, and soils that are high in organic matter, bicarbonate or phosphate are especially prone. The agronomic consequence is yield loss. The public health consequence is grain with low zinc content, which contributes to dietary zinc deficiency where rice is the main source of calories. In Malaysian granary areas such as MADA and KADA, soil and plant testing is the way to find out which blocks are affected.
How zinc deficiency shows up
Zinc deficiency in paddy shows as yellowing of young leaves, stunted growth and reduced tillering in the vegetative stage. In severe cases, panicles are small and grain fill is poor. In practice, losses often occur below the threshold of obvious visual symptoms, so the deficiency reduces potential yield without triggering the visible distress that would prompt corrective action.
The human nutrition connection
Zinc in rice grain comes partly from uptake during grain filling and partly from remobilisation of zinc stored in leaves and stems. A crop grown on zinc-deficient soil tends to produce grain that is low in zinc, and milling removes the zinc-rich bran, so populations that rely on polished rice for most of their calories are at higher risk of dietary zinc deficiency.
Agronomic biofortification, applying zinc fertiliser to raise grain zinc, can address the nutritional gap and, on deficient soils, the yield loss as well. In 17 field trials in China, India, Lao PDR, Thailand and Turkey, foliar zinc sprays clearly raised zinc in brown rice, especially when applied after flowering, while soil zinc alone did little for grain zinc. Zinc had little effect on yield at most of those sites, which is why confirming deficiency comes first (Phattarakul et al., 2012).
Agronomic zinc application: what the data shows
Zinc sulphate applied to the soil at land preparation or early tillering is the usual way to correct deficiency for the crop, with the rate set from soil tests and local recommendations. Incorporating it before flooding improves contact with the root zone as the crop establishes. Foliar zinc sulphate is a complementary approach, and sprays after flowering are the more effective route for raising grain zinc.
Soil organic matter also matters for zinc. SoilBoost EA, a humic acid soil conditioner applied at land preparation, adds humic substances that can complex zinc and may help keep it available as soil conditions change after flooding. CSB Organico provides additional organic matter through the growing season.
Start with a test
On soils confirmed as zinc-deficient, zinc application is one of the simpler corrections to make, and the response is most reliable where the deficiency is clear. Confirm soil and plant zinc status by testing first, then weigh the cost of zinc against your own yields and paddy prices.
References
- Phattarakul, N., Rerkasem, B., Li, L. J., Wu, L. H., Zou, C. Q., Ram, H., Sohu, V. S., Kang, B. S., Surek, H., Kalayci, M., Yazici, A., Zhang, F. S., & Cakmak, I. (2012). Biofortification of rice grain with zinc through zinc fertilization in different countries. Plant and Soil, 361, 131-141. https://doi.org/10.1007/s11104-012-1211-x
Related products from Chemiseed
Supporting micronutrient management and paddy soil health:
