Mar13

IRRI agronomy challenge: a little bit more nitrogen

Author // Dr. Achim Dobermann Categories // Achim Dobermann's blog

March 10

 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.

Achim assesses if the crop neads more nitrogen
by using the IRRI Leaf Color Chart.

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So far we have applied about 130 kg N/ha, but it is always difficult to know whether that is enough or it 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.

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About the Author

Dr. Achim Dobermann

Dr. Achim Dobermann

Achim is a soil scientist and agronomist with 25 years experience working in Asia, North America and Europe. He is recognized internationally as an authority on science and technology for food security and sustainable management of the world's major cereal cropping systems. He has authored or co-authored over 250 scientific papers and two books on nutrients in rice and has received numerous awards from various academic, government and industry organizations. He is a Fellow of the American Society of Agronomy and a Fellow of the Soil Science Society of America.

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