Boron deficiency-an overshadow for paddy yield

By Awais Ahmad and Muhammad Imran Azeem

RICE IS one of the major staple food crops of Pakistan and presently the area under rice cultivation is almost 2.3 million hectare (M ha). It not only fulfills our domestic requirement but also a good source of foreign exchange. Our national average yield is 2.00 tons per hectare. Although we are producing good quality rice but we are lagging behind major rice producing countries like China and India, etc. in per unit area production. The underlying reasons are low organic matter in the soil, high soil temperature, intensive cultivation and significantly imbalance nutrition. Most of the time, rice growers replenish the soil with necessary macronutrients like nitrogen, potassium, phosphorous neglecting the micronutrients like zinc, boron, etc. that are equally important. Boron, a micronutrient, is of immense importance for rice because of its role in reproductive system and metabolic activities. It is also unique in enhancing the grain quality. It is alarmingly deficient in Pakistani soils where rice is grown (collar tract). We can economically increase the paddy yield up to 30 per cent by the judicious use of boron.

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Pakistan is the 4th largest rice exporter, contributing 30 per cent of Asian rice exports. Average rice production of the world is 4.3 ton/ha while some countries have claimed much higher production. China and India claimed up to 19 ton/ha that is exceedingly high. In Pakistan, rice is mainly grown in North-East Punjab, having areas of Sialkot, Gujranwala, Narowal, Hafizabad, Sheikhopura, Lahore, Okara, etc. During the last decade, Pakistan has witnessed a continuous decline in paddy production.

The rudimentary cause of this decline in paddy yield is the least use of micronutrients although several other factors like wet and dry seasons, low organic matter in the soil, high soil temperature, intensive cultivation, leaching of the nutrients impede the paddy production, too. The aforementioned core regions of rice cultivation follow a rice-wheat cropping system that exhausts the soil. We have to nurture the soil with essential nutrients to harvest maximum yield. Most of the time we fertilize the soil with macronutrient fertilizers like Urea, DAP, Potash. Urea is the most applied fertilizer by the marginal farmers. Though commercial farmers use all the recommended fertilizers, but they are just a small fraction of the farming community. According to an estimate, about 45 per cent of the soils are deficient in Boron where rice is mainly grown.

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Boron is the second most important micro-nutrient for rice after Zinc (Zn). It is important both in vegetative as well as reproductive growth. It is involved in a number of physiological processes including metabolism and translocation of carbohydrates, RNA metabolism, enzymatic activity and respiration. Many processes like pollination, pollen grain germination, pollen tube elongation, fertilization and embryo formation are very sensitive to boron. It enhances the grain quality by increasing the starch contents, quality index, kernel elongation, and bursting upon cooking. It is critically important in the above mentioned processes and even its slight deficiency can seriously limit the paddy yield.

On an average, rice plants suffer 40 per cent male sterility. Boron deficiency increases male sterility and sometimes even the absolute failure of the reproductive organs. The thinner tillers die before the onset of reproductive phase and which survive they fail to produce viable seeds.

Boron is immobile in plants so its deficiency symptoms appear firstly on younger leaves. But it is extremely difficult to visualize boron deficiency symptoms as it is involved in metabolic and physiological processes and its deficiency symptoms dont appear at early plant growth stages.

Rice requires a narrow range of Boron of almost 3-5 kg per hectare as soil application and 200 litres of 1 per cent boron solution as foliar application in case of severe deficiency. Borax, Boric acid, Sodium Borate, Solubor, and Sodium tetra-borate can be used as boron fertilizers. The choice of boron source, rate of application and method should be decided according to the soil analysis report, crop stage, and severity of deficiency.

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Boron deficiency is not only limiting paddy yield but also deteriorating the grain quality as well. This in turn is depreciating our basmati rice in the international market. The government should realize the gravity of the situation and take some concerted steps to eradicate the problem. As most of the rice growers are unaware of the importance of the boron application in rice, agricultural extension department and private input supply companies should use their grey matter in educating the farming community regarding this. There should be site specific boron deficiency mapping in the rice growing regions at district level soil testing laboratories, and if possible at micro level. To convince the farmers to apply boron, adaptive research stations should also conduct demonstration plots. By doing so, we can substantially increase the paddy yield which will bring enormous foreign exchange.

The writers are MS Scholars in the Agricultural Sciences at King Saud University, Riyadh, Saudi Arabia.

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