Food security is an important task to nourish the rapidly growing population of the world. However, increasing food demand and declining water availability are the challenges for food security. Water scarcity is perhaps the foremost limitation for sustainable crop production, rice being the most vulnerable.
During transplanting and crop establishment, the fields remain flooded with 5-10 cm of water. As much water is used for wet soil preparation for rice production and also the huge losses occur by seepage, percolation and evaporation when the soil is flooded, the production of rice by this conventional method requires a large amount of water. To produce 1 kg of rice, it takes 3,000-5,000 L water, which is about 2 to 3 times more than to produce other cereals such as wheat or maize. With continuous decreasing water resources, it is estimated that about 17 Mha of conventional rice producing areas may face “physical water”.
Several water-saving rice production systems, such as alternate wetting and drying and aerobic rice are being propagated worldwide. This approach saves water by eliminating continuous seepage and percolation, reducing evaporation, and eliminating wet-land preparation. Aerobic rice is grown in non-puddled, aerated soil without standing water in the field with supplementary irrigations to cope with water requirements in the soil up to field capacity, thus saves a significant amount of water.
Although water-saving production systems have much potential of saving water but several factors are hindering the wide scale adoption and potential benefits of these systems. Several problems including vulnerability to rice blast, a weak ability of the seedlings to emerge through the soil surface, and low vegetative vigor limit the widespread adoption of aerobic rice. In addition, aerobic rice is more prone to weeds, pests, panicle sterility and lodging problems resulting in substantial yield losses. It is, therefore, necessary to develop apposite management strategies to overcome the above stated problems for maximizing the returns on sustained basis.
Non-saturated soil cultures, as in water saving rice production systems, are known to unfavorably affect not only rice growth but also increase spikelet sterility. Less number of grains per panicle as a result of panicle sterility is one of the main reasons for low yield of aerobic rice. Water act as a heat sink to buffer large fluctuations in temperature and deficiency of it cause floret sterility. Moisture stress which is more common in aerobic culture, during flowering and grain filling increases spikelet sterility about 40 per cent.
Boron (B) is an essential nutrient for plant growth and development. As required in small amounts by plants so called as micronutrient. In plants, B takes part in nucleic acid, carbohydrate, protein, phenol and indole acetic acid metabolisms, cell wall synthesis, membrane integrity and its functioning. Boron is also associated with one or more of the processes of calcium utilization, cell division, flowering and fruiting, carbohydrate and nitrogen metabolism, water relations, and catalyst for certain reactions and its deficiency is more common in crops that are cultivated in soils that have higher amount of free carbonates, high pH and low organic matter.
Boron availability is associated with soil moisture conditions and limited soil water often limits the B availability. Boron deficiency generally appears as soils become dry. In alkaline soils, availability of B under aerobic conditions is reduced as its availability to plants decreases with increasing soil pH, especially above 6.5. Under such conditions, the only possible solution is the application of B in such a way that plant may able to attain it for normal functioning. Boron deficiency not only causes severe reduction in paddy yield but also deteriorates its kernel quality and is identified as one of the most important factors causing sterility in cereals because of poor development of anthers and pollen and failure of pollen germination.
As sterility results in poor grain filling causing severe reduction in yield, with increasing demands for food security the problem becomes more prominent. Solving this dilemma is a challenge for researchers. For efficient uptake of B by the plant, application method plays a vital role. Among different practices, seed priming can be used as an effective physiological strategy. Soil and foliar applications are the most prevalent methods of B addition in the developed world. However, seed treatments, which include seed priming and seed coating, are an attractive, cost-effective, environmental friendly approach to improve the yield of aerobic rice. However, further experimentation is required to find out the exact requirement of different cultivars planted in the various types of the soils to meet the ever increasing requirement of the food across the globe and to make the country self sufficient in its food production sector.
The first author is M.Sc. (Hons.) Agriculture, Agronomy, University of Agriculture Faisalabad, and the second author is Associate Professor, University of Agriculture Faisalabad, Pakistan.