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April 15, 1999
To the Butte County Rice Industry:
Nitrogen Management in Akitakomachi
In response to increased grower interest in growing premium quality Japanese varieties of rice, research was conducted over the last three years to determine the optimal rate and time of nitrogen fertilization. Proper nitrogen management is one of the key components of producing high quality Akitakomachi rice. Below, I present a summary of the research results. If you would like more detail or some information on Koshihikari, please give me a call at (530) 538-7201.
Bear in mind that these results should be considered in the context of your farming operation. They are not absolute under all conditions. Consider such factors as field history and the inherent productivity of a field (yield potential) when designing a fertility management program.
Akitakomachi (Akita) was fertilized with quantities of nitrogen ranging from 0 to 120 lb N/acre. The nitrogen was applied either all preplant or split applications applied at various stages of growth. Split applications were applied at mid-tiller, panicle initiation, pollen meiosis, heading, and post heading. Among these split treatments only preplant and preplant/panicle initiation were useful. Results pertaining to only those treatments are presented. Potassium and phosphorus were managed normally.
Nitrogen Fertilization. The top three yielding treatments (1996 & 1997 average) were 80-0-0, 100-0-0, and 50-50-0, producing 6488, 6339, and 6145 lb/a, respectively (Table 1). However, the 80 and 100 lb N/acre preplant plots consistently lodged earlier than the other treatments. Early lodging may reduce rice quality. Quality concerns are extremely important if the rice is for export to Japan.
Yields were down in 1998, reducing the yields when considered as a 3-year average (Table 1). Interestingly, Akita responded differently in 1998 to N treatments, where the split application treatments produced the highest yields and the all preplant N the lowest. Results from 1996 and 1997 may be more applicable to this year because of the relatively open spring we are having thus far.
 
Table 1. Yield of Akitakomachi grown at different rates and application times of nitrogen. Treatments indicate the amount of N (lb/a as ammonium sulfate) applied at preplant, panicle initiation (PI), or heading (H). For example, 50-50-0 represents 50 lb N preplant, 50 lb N at PI, and 0 lb N at H.
Treatment 96-97 Avg Rank 3-yr Avg Rank
80-0-0 6488 1 5963 3
100-0-0 6339 2 5983 2
50-50-0 6145 3 6029 1
40-40-0 5935 4 5723 5
60-0-0 5922 5 5627 8
50-0-50 5806 6 5792 4
40-20-0 5685 7 5647 7
40-0-40 5606 8 5677 6
40-0-0 5544 9 5615 9
40-0-20 5393 10 5560 10
20-20-0 5294 11 5329 12
20-0-20 5245 12 5441 11
Taste Scores. Yield is not the only consideration. The Japanese market demands certain grain quality characteristics. Among the factors which can affect the marketability of rice in Japan are taste scores, fissuring, and odor. Taste scores for white rice are a function of protein, amylose, and moisture content. For brown rice, fatty acid content is an additional factor. Generally, taste scores of 75 or better are required. Taste scores for the high yield treatments ranged from a low of 69 in 1998 to a high of 83 in 1996 (Table 2).
Table 2. Taste scores for Akitakomachi grown at different rates and times of nitrogen application in 1996 (experiments a & b), 1997, and 1998.
Treatment 96a 96b 97 98 Average
80-0-07581776976
100-0-07880776776
50-50-07679796976
40-40-07981777076
60-0-07883776977
The lower taste scores in 1998 were attributable to higher grain protein and moisture content at harvest. Protein content is negatively correlated to taste scores. In that, increasing protein results in decreasing taste scores. Thus, managing nitrogen to keep grain protein low is key. Drying techniques can also influence taste scores and other quality parameters.
Leaf Nitrogen. Good yields and taste scores were observed when the leaf tissue N content was around 2.5% at panicle initiation. If you decide to top dress based on leaf tissue N content, Table 3 can be used as a guideline when using either the Minolta chlorophyll meter or the Fuji color chart.
Table 3. Estimating leaf nitrogen content in Akitakomachi using a Minolta chlorophyll meter or Fuji color chart.
Chlorophyll meter value
 
262728293031323334353637
% N1.92.02.12.32.42.52.62.72.82.92.93.0
Color Chart Panel
 1234567
% N1.62.02.52.93.33.74.0
Harvest Moisture. Designed experiments to determine optimal harvest moisture content for head rice yields will be conducted this summer. Field samples harvested at various moisture contents at the RES (raw data provided by K. McKenzie) indicate that head rice yields peak at 23%. Timely harvest is critical. Harvesting too wet results in low taste scores and too dry in fissured kernels. Preliminary observations indicate the optimal harvest moisture is a narrow window of opportunity.
Prepared by: Cass Mutters

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Modified: 3 May 1999 Comments to jayoung@ucdavis.edu