Information from 1996 Missouri Rice Research Update.

Potassium and Phosphorus Nutrition in Rice 1

Michael Aide and Jennifer Picker 2


Proper potassium (K) nutrition in rice promotes: (1) tillering, (2) panicle development, (3) spikelet fertility, (4) nutrient uptake of nitrogen and phosphorus, (5) leaf area and leaf longevity, (6) disease resistance, (7) root elongation and thickness, (8) and culm (stem) thickness and strength. Deficiencies of K are exhibited by (1) dark green leaves with brown spots along the midvein, which eventually coalesce across the entire leaf, (2) decreased culm thickness, and (3) decreased lignification portion of the K is returned to the land after harvest.

Phosphorus (P) deficiency symptoms appear in the lower part of the plant and results in (1) decreased leaf number, (2) decreased leaf blade length, (3) reduced panicles/plant, (4) reduced seeds per panicle, and (5) reduced filled seeds/panicle. The reduced tillering capacity for rice planted in an P impoverished soil is usually greatest factor responsible for reduced yields. Flooding rice soils generally moderates the pH towards a neutral pH condition, thus promoting the availability of soil P.

Materials and Methods:

The experiment was conducted at the Missouri Rice Farm in Dunklin county, MO. Lemont was planted in late-May, followed by population estimates after emergence. Nitrogen fertilization consisted of 120 lbs N/a as urea immediately prior to flood and two 30 lbs N/a treatments at midseason. Weed control consisted of 3 quarts of Stam (proponil)/a followed by a second application prior to flood.

Tissue analysis occurred in late-June and late-July. Nitrogen and sulfur were determined by a C-N-S analyzer. Calcium, Mg, Al, P, K, Zn, B, Fe, Mn, Cu, Na were determined by inductively coupled plasma emission spectroscopy after acid digestion of ground plant tissues. Field measurements involved tiller counts, the number of spikelets/panicle, the percentage of fertile spikelets, seed weight, and yield. Tiller counts were obtained at midseason to estimate the number of panicles/plant and were determined by sampling 10 random plants. Spikelet counts were determined by selecting 20 random plants and sub-selecting 10 average panicles for seed counting. Harvest (15 Oct 96) was by plot combine, followed by seed moisture determination. Data analysis involved analysis of variance, regression analysis, and correlation analysis using Quattro-Pro.


Soil sampling revealed that the test areas was strongly deficient in P and K, however, considerable variability did exist across the block design. Typical P and K levels were less than 10 and 60 lbs P2O5 and K2O/a, respectively. Soil pH was 4.9 and 5.4 in CaCl2 and water respectively. Rice leaf tissue elemental concentrations demonstrate that N, S, Mg,

Table 1. Tissue concentrations for a K x P rice fertility trial.

Treatment   N    S    P    K    Mg    Ca    Fe    Mn    Cu    Zn
lbs K2O/a ------------  %  -------------    ---------  %  ------
   0      3.9  0.23 0.23 0.94 0.28  0.38   101    873   4.6   22
  30      3.6  0.23 0.24 1.03 0.30  0.39   100    879   6.4   22
  60      3.6  0.22 0.22 0.98 0.27  0.37    95    844   5.8   19
  90      3.6  0.22 0.22 1.03 0.27  0.37    95    878   5.6   20
Expected  3.2  0.25 0.33 1.65 0.13  0.29   120    105   6.0  190

1 Potassium (K) tissue concentrations at 30,60, and 90 lbs K2O/a were significantly higher than control at 5% level of probability. Nitrogen, S, P, Mg, Ca, Fe, Mn, Cu and Zn were not significantly different. 2 Expected values are from Midwest Laboratories (Omaha, Nebraska).

Table 2. Yield components for a P x K experiment involving rice.

Treatment     Tillers     # Spikelets/panicle        Yield
lbs K2O/a        #       total        fertile    lbs/a    kg/ha
   0           4.8a       99a           84a       6620    7410a
  30           4.5a      100a           88a       6920    7750a
  60           5.1a      104b           83a       7440    8330b
  90           5.0a      108c           84a       7660    8580b 

1Within a column, different letters represent significant differences at the 5% level of probability. 2Means are pooled across phosphorus treatments.

Ca, Fe, and Cu closely approximated the expected values for rice. These elements, however, did not demonstrate significant differences because of the P and K fertilization treatments. Additionally, P levels in leaf tissues did not show significant differences because of P or K fertilization. Additionally, all P leaf tissue levels were slightly deficient, suggesting an impoverished soil. Zinc showed a strong uniformly excessive concentrations across all treatments. Potassium fertilization did slightly elevate K tissue concentrations above that of the control.

Analysis of the elemental concentrations of rice tissue, the extent of tillering, the number of spikelets/panicle, and yield showed no differences because of phosphorus fertilization. Table 2 presents the mean values for tillering, panicle development and yield for the K treatments pooled across all P treatments. Potassium did not significantly affect tillering, likely attributed to the extremely low initial Pl and K levels in the soil. Potassium promoted panicle development and rice yield, especially at the highest K rate.

At $7.00/cwt, the difference in yield between the 30 and 60 lbs K2O/a treatments equates to a return to grower of $40.60. The cost of the additional potash (0-0-60) is $2.16/a, thus a net return to the grower is $38.44.


Phosphorus fertilization at 50 lbs P2O5/a did not significantly affect either the rice leaf tissue P concentration, tillering panicle development, or yield. Potassium fertilization at 60 and 90 lbs K2O/a significantly increased panicle development and yield. The Missouri Soil Test Recommendation Handbook (Buchholz, 1987) recommends 20 lbs K2O/a, thus additional efforts need to be focused on potassium fertilization rates for rice in Southeastern Missouri.


Buchholz, D.D. 1987. Soil test interpretations and recommendations handbook. University of Missouri, College of Agriculture. Columbia, Missouri.

DeDatta, S.K., and D.S. Mikkelsen. 1985. Potassium nutrition in rice. p. 665-699. In R.D. Munson. Potassium in agriculture. American Society Agronomy, Madison, WI.

Nelson, L.E. 1980. Phosphorus nutrition in cotton, peanuts, rice, sugarcane, and tobacco. p. 693-736. In F.E. Khasawneh, E.C. Sample, and E.J. Kamprath. The role of phosphorus in agriculture.

(1) I wish to acknowledge the Missouri Rice Research and Merchandising Council for financial support; and Steven Hefner, University of Missouri Delta Center for field supervision of this project.
(2)Soil Scientist and Graduate Student, Southeast Missouri State University

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