Management of rice production systems to increase productivity

3.1.4. Improved Water Management System – Repeated Wetting and Drying
Many irrigation systems do not maintain adequate drainage
mechanisms. Drainage canals are rarely cleaned, and because farmers believe
that rice does best if water is supplied in abundance, they do not see a need for
a drainage system except at harvest time. This practice is not only wasteful,
but it also leads to leaching of soluble nutrients, inhibits or changes soil
microbial finally activities, slows down mineralization and nutrient release
from the soil complexes. Celton and Marquette (1972) reported that good
water control on Madagascar Tananarive Plains resulted in rice yield increases
of 155 to 261%. In 1993 the Madagascar’s Agricultural Extension Ministry
reported similar increases in rice yield due to water control. Bhuiyan et al.,
(1994) reported yields of 6.7T and 7.4T in the Philippines under soils saturated
throughout the growing period for wet‐seeded and transplanted rice,
respectively.
3.1.5. Influence of Repeated Wetting and Drying on Soil Microbial Activity
……...and Nitrogen Mineralization
Worldwide nitrogen is the most limiting nutrient to rice production;
therefore increased nitrogen use efficiency will translate into yield increase. In
spite of extensive research and advances in fertilizer management, rice in the
lowlands generally utilizes less than 40% of applied N, mainly because of N
losses that occur via NH3 volatilization from the floodwater after NH3
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