Achim Dobermann, deputy director general for research at the International Rice Research Institute (IRRI; http://irri.org ), and Leigh Vial, head of IRRI's experiment station, are conducting a special project, the IRRI Agronomy Challenge, in which they are demonstrating how to grow a productive rice crop in a 25 x 100-meter field on IRRI's research farm.
In this installment, Dr. Dobermann shows how to use the Leaf Color Chart (LCC; http://irri.org/index.php?option=com_k2&view=item&layout=item&id=10980&l... ) in the field to determine if the crop has a proper nitrogen level.
Commentary by Dr. Dobermann:
"63 days after sowing and there's really not a lot more we can do. All major crop management decisions have been made, but I went out this morning to check one more time on the nitrogen status.
So far we have applied about 130 kg N/ha, but it is always difficult to know whether that is enough or may even be too much because so many things affect how much nitrogen is available to the plants and how much they actually need.
I took about 15 Leaf Color Chart (LCC) readings at different places in the field -- a simple tool to check on the greenness of the leaf as an indicator of plant nitrogen status. The readings ranged from 2.5-3 on the 4-panel IRRI LCC, with an average of 2.8. At this stage, a value of 3 or above would be considered sufficient for a direct-seeded semi-dwarf indica variety. Since the average was below three, I decided to apply a small amount of additional nitrogen, about 20 kg/ha.
All in all the whole affair took just a little more than half an hour, so it's really not hard or costly to do, but may make a difference in final yield and profit. The theory is that applying a late nitrogen dose at early heading may delay leaf senescence and enhance grain filling. We'll see about that. Altogether we have applied about 150 kg N/ha, which is a rate that is quite common for an irrigated dry season rice crop in our region."