Boron Deficiency in Rice
This deficiency can affect rice throughout its growth cycle but symptoms usually appear first on young leaves. The tips of the emerging leaves turn white and rolled, and occasionally become necrotic. In severe cases, growing points become brittle and die. Plant growth is stunted, new tillers continue to emerge but the stems are thinner and flexible. When infected at panicle initiation stage, the plants fail to produce fertile panicles. Boron deficiency has a serious impact on crop productivity. Both the rice grains quantity and quality is lower. Because they contain less starch, grains become stickier than usual after cooking.
Boron deficiency affects the structure and integrity of the cell. Boron deficiency is not very common in rice, but it can occur if the right conditions are met. Highly weathered soils, acid soils and sandy soils are especially prone to boron deficiency as well as soils derived from igneous rocks or from marine sediments. High organic content and liming also affect the availability of boron negatively. The uptake of boron by plants is determined by the soil pH and its concentration in the soil. The micronutrient is not very mobile, this is why the first symptoms usually appear on forming leaves. Boron deficiency is more likely in plants suffering from a water deficit. However, wetting and drying cycles increase the amount of boron fixation. In saline soils, boron helps plants to cope with salt stress.
A compost mix of animal manure and leaves is ideal to provide plants with organic matter and nutrients such as sulfur and boron. This is a long-term approach to remedy boron deficiency.
To avoid deficiencies, apply boron in soluble forms (borax) for rapid treatment (0.5−3 kg/ha), if possible before planting. It can also be used as foliar spray during vegetative rice growth. It is not recommended to mix borax or other boron sources with ammonium fertilizers. In the field, sources of boron that last in the soil (e.g., colemanite) can be applied at intervals of 2−3 years. The rate will depend on the type of soil, 2-3 kg/ha in silty and clayey soils and 3-5 kg/ha in sandy soils. In rotation systems with wheat, the boron applied to wheat can alleviate boron deficiency in the subsequent rice crop.