WHAT IS THE IMPORTANCE TO KNOW ABOUT 'DAY LENGTH' IN AGRICULTURE?
The length of the day (roughly from sunrise to sunset) varies with the seasons and with of Latitude. In Malaysia as a Tropical Country the sun arise fo 12 hours everyday throughtout the years except during monsoon seasons. I would like to talk about the importance of day length based on my reading from few books by Longman. Seasonal variation is the greatest at high lalitudes and least at he equator like Malaysia, Indonesia and Central America. Our day length is constant all year round so that we able to grow parrenial, short term crop and herbaceous crop all year round. The rubber, oil palm, tropical fruits, leafy vegetables, fruit vegetables, paddy, grain corn and many other food crop are producing in hugh volume.
In the nothern hemisphere the longest day is 21 June and the shortest day is 22 December (The summer and the winter solstices) when the sun is frurhest north and south of the equator. I never been imagined of having such experience on that particular place in my life. The opposite seasonal variation of a day-length occurs in the southers hemisphere. On the vernal and autumnal equinoxes (20 March and 22 or 23 September) the sun is overhead the equator in its passage north and south, and everywhere the days are 12 hours long. Those are extreme high latitudes near the poles the length of the days varies from 24 hours in the mid-summer to 0 hours in the mid-winter, while in the equator it was 12 hours all year round. What a great creation of Allah in this nature of the world. The greatest seasonal variation at the highest latitudes within the tropics of Cancer and Capricorn is from winter days of about 9 hours to summer days of about 15 hours to make it 24 hours a day.
Back to our main discussion on the importance of knowing the mportance pf day-length to agriculture. Many temperate crops are reproductively long-day plants, but tropical crops are either apparently insensitive to day-length (For example groundnuts, corn, oil palm, annual cottons, cocoa, some varieties of rice and some grain legumes), while others flowers or produce tubers only in response to short or shorthening days (for example , some shorgums, pearl millet cultivars, some rice, some potatoes and some grain legumes). I notice this crop during 4 credit hours lectures in university way back in 1998. Eventhough I do talk about the importance of the day-length , we must also understand the important of teh length of the night which is physiologigally important in photoperiodism. It related to the flowering process of the crops.
As I remember during my lecture, cultivars of photosensitive crops, whether they are temperate or tropical have day-length requirements for infloresence initiation and flowering which tend to ensure that the flower able to produce fruits. In Malaysia the long-day with dry condition in january to February induce the tropical fruits such as Durian (Durio zibethinus), Rambutan (Nephelium spp), Duku (Lansium domesticum), Mangoesteen (Mangostana indica), Cempedak (Artocarpus chempeden) and many other fruit crops to flowering in April or May every year.