Cereals processing technology

92 Cereals processing technology
5.3.4 Photoperiod
The photoperiod represents the duration of the light period between sunrise and
sunset. It is a major factor influencing the development of the rice plant,
especially its flowering characteristics. Photoperiod-sensitive cultivars flower
when the decreasing day length reaches a critical point. Day length also exerts a
large effect on the growth duration of rice cultivars, depending upon their
photoperiod sensitivity. The response is seen largely through changes in the
basic vegetative growth pattern, especially the duration of the reproductive
phase. Photoperiod sensitivity (the critical day length required for flowering)
varies greatly, some cultivars being referred to as nonseasonal or neutral, others
as weakly photoperiod sensitive, and others as strongly photoperiod-sensitive.
5.3.5 Solar radiation
Solar radiation and sunshine hours are important climatic determinants in rice
production. Young seedlings have a comparatively low solar radiation requirement.
Light becomes progressively more important through the vegetative and
reproductive phases, reaching maximum importance at the heading stage. The
need for solar energy is most critical from panicle differentiation to about ten
days before maturity. Rice yields are strongly correlated with total solar
radiation between thirty and forty-five days before harvest. The amount of
sunlight a crop receives depends on solar radiation intensity, day length, cloud
cover, and mutual shading by the plants in a population.
5.3.6 Weed pests
Weeds are universal competitors of rice, competing for moisture, light, and plant
nutrients. Weeds also create problems in harvesting, drying, and cleaning, and
reduce the quality and marketability of the crop. Insects pests such as
leafhoppers and stemborers also live on weeds as alternate hosts and directly
attack the rice crop. Water management is often impeded when weeds block
irrigation systems, slowing drainage.
There are over 30,000 weed species regarded as serious rice pests in the
world. Of these, 30 species are very damaging and some 88 species are noxious.
Since rice is grown under such a wide range of climatic conditions, soil types,
and crop rotations, it is not possible to identify the most damaging species.
Echinochloa crusgalli, E. colonum, Cyperus rotundus, Rottboellia cochinchinensis,
and Imperata cylindrica are serious weed pests in most upland rice areas
of the world. 8 The most common means of weed control in tropical areas is hand
weeding, usually with a short-handled hoe. Without satisfactory weed control,
upland rice yields are severely restricted.
5.3.7 Rice culture and production methodology
Based on land and water management practices, ricelands are classified as either
lowland (wetland preparation of fields) or upland (dryland preparation of fields).