Soil Health

Micronutrients are elements that are essential for plant growth, but are only required in small quantities. They include zinc, manganese, iron, copper, and several others. There is at least a small amount of these elements present in all soils, and often there is no need to add them to achieve healthy plant growth. However, there are two general cases in which it is helpful to add them: 1) when other soil components interact to make a micronutrient unavailable for plant uptake; or 2) when plant yields are very high (due to optimum management of macronutrients and mitigation of common crop growth constraints) so that large plants are using up the small amount of micronutrients available in the soil.

For irrigated rice systems, zinc is the most common micronutrient deficiency while iron is the most common micronutrient toxicity. This is because flooding the soil causes biochemical changes that make zinc less available, while iron becomes more available to rice plants. It is possible to partially mitigate both of these micronutrient problems by carefully allowing the soil water level to go about 10 cm below the soil level for a short amount of time (5-10 days) prior to re-flooding. Another strategy to deal with these micronutrient problems is to breed varieties that are tolerant of their constraints.

A third strategy to deal with zinc deficiency is to add zinc-containing fertilizers to the soil. However, it is very difficult for rice growers to identify or predict zinc deficiency in their fields because it tends to be very specific to the site and the season. Because zinc fertilizer is much more expensive per kilogram than NPKS fertilizers, it is not profitable for growers to apply zinc if they are not sure it is necessary. Also, some of the same biochemical processes that cause soil zinc to become less plant-available after flooding also occur with applied zinc fertilizers. In other words, a grower may apply a zinc-containing fertilizer to a rice field without having any effect because the zinc from the fertilizer turned in to an unavailable form before the plant could use it. Our research is focused on helping growers identify when it is necessary to add zinc and to provide recommendations about the best way to apply it so that it stays available to the rice plants.

Zinc is also an important micronutrient for humans. Read more about our work on high-zinc rice varieties and how we help improve human nutrition.