Information from 2000 Missouri Rice Research Update, February 2001.

Boron Fertilization of Rice

David Dunn and Sarah Jones

Abstract:
Boron fertilizer treatments were applied to a rice field that the soil tested low for boron. Soil and foliar applications were compared on Kaybonnett rice. Boron treatments increased rice yields, on average, 8 to 25 bushels per acre. The greatest rice yield was obtained with a 0.5 lb/a foliar application at first tiller growth stage.

Introduction:
Boron is an essential plant nutrient. Its functions in rice plants are involved in cell growth and development of the flower. Boron is very water-soluble. As such it is mobile in soil-water solutions. Current University of Missouri soil test recommendations for rice are to apply 0.5 lb/a boron application when less that .25 ppm of boron is found in the soil. Soil samples collected at the Missouri Rice Research Farm in 1998 were found to contain between .02 and .35 ppm boron.

Materials and Methods:
In this two year study, a location at the Missouri Rice Research Farm that tested low in soil boron (0.19 ppm average) was used to conduct this evaluation. Kaybonnett rice was drill seeded at a rate of 75 lb/a. Weeds were controlled with propanil applications, at 3 lb./acre when the grass had 2-3 leaves and then reapplied approximately 14 days later, shortly before flood establishment (Stam 3+3 program). No insect control was necessary. In this study four Boron application rates, .25, .50, .75, and 1.0 lb B/a, were compared to an untreated check. Two application methods, preplant soil applied and preflood (first tiller) foliar spray, were evaluated for each boron rate. Soil samples were collected prior to flooding from each plot receiving preplant boron.

These soil samples were tested for plant available boron. Each plot was mechanically harvested and the yield recorded.

Results:
All boron applications increased rice yields over the untreated check (Table 1). In 1999, the foliar applications produced higher yields than soil applied boron. The average for all four boron treatments in an application type was also greater in the foliar in the first year of the project. In 2000, the soil application for the same rate of fertilizer was greater. The same is also true for the 2000 average for the four treatments. The two year average, however, showed the soil applications produced greater yields for the same boron application rate. The 0.5 lb B/a for both soil and foliar applications (170bu/acre) showed the greatest increase compared to the untreated check (145 bu/acre)

Table 1.  Average rough rice yields for boron 
treatments in 1999 and 2000 for the rice variety 
Kaybonnett.

lb. B/a      Application   Average rough rice 
             type          yields (bu/a)
---------------------------------------------
                         1999    2000    Mean
0                        146     144     145
0.25         Soil        150     165     158
0.5          Soil        151     189     170
0.75         Soil        150     173     162
1.0          Soil        147     185     166
---------------------------------------------
Average      Soil        150     178     164
---------------------------------------------
0.25         Foliar      151     169     160
0.5          Foliar      160     180     170
0.75         Foliar      149     157     153
1.0          Foliar      151     154     153
---------------------------------------------
average      Foliar      153     165     159
---------------------------------------------

Soil applications of boron increased plant available soil test levels (Table 2). The magnitude of this increase was not consistent with the application rate.


Table 2.  Average soil test B levels for 
preplant soil applied treatments.


lb B/a  Application   Soil Test B in ppm
------------------------------------------
                      1999    2000    Mean
0                     0.17    0.21    0.19
0.25    Soil          0.24    0.30    0.27
0.5     Soil          0.43    0.33    0.38
0.75    Soil          0.37    0.42    0.40
1.0     Soil          0.49    0.54    0.52

Conclusion:
Rice yields can be increased with boron applications. On the two year average, maximum yields were obtained when the University of Missouri recommended rate (0.5 lb B/a) of boron was applied. In 1999, the foliar application was better than the soil. While in 2000, soil applications were better than the foliar. But for the two year average, the soil is on top. Producers should consider testing soils for boron and applying boron when the soil test B levels are found to be less than 0.25 ppm.

Take Home Message:
Next year the plan is to try mixing the Boron into the Stam 3+3 program, so as to eliminate an extra trip around the field. Also, for those who decide to use the soil application of Boron, the fertilizer Granubor will cost approximately $2.50/lb. The foliar application, Solubor, will cost about $3.00/lb.

Acknowledgement:
We would like to thank the Missouri Rice Research and Merchandising Council for their generous and continuing support for this project.

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