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,
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
2 Expected values are from Midwest Laboratories (Omaha,
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
Buchholz, D.D. 1987. Soil test interpretations and recommendations
handbook. University of Missouri, College of Agriculture. Columbia,
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.