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Potassium and Phosphorus Nutrition in Rice.

Michael Aide [*]

Abstract: Rice (Oryza sativa L.) is one of the world's premier food crops and is an important commodity in the Lower Mississippi River Valley. Successful production requires a consideration of soil fertility, particularly N, P, and K. Potassium and P soil fertility investigations are relatively rare compared with those of N. The objective of this investigation was to evaluate the P and K soil requirements for rice. The research was conducted at the Missouri Rice Research Farm in Dunklin County, Missouri. The experimental design consisted of four rates of K and two rates of P in a four replicated randomized block design. The rice variety 'Lamont' was planted in 1996 and 1997 and fertilized with potash at 0,1 2 and 3 times the soil test recommendations and superphosphate at 0 and 1 times the soil test recommendations. The yield components (population, panicle density, spike development, and yield) and elemental concentrations of rice tissues were performed to assess agronomic performance. Phosphorus did not inf luence any of the yield components, including yield. Potassium at twice the recommended rate significantly increased the yield and was justified when compared to the cost of the additional potash. The yield advantage was attributed to increases in the tillering capacity of the rice plant and spikelet production. Based on these results, soil K recommendations in Missouri for rice may need to be adjusted upward.

Rice (Oryza sativa L.) is a freely tillering annual grass presenting a highly branched and shallow root system with a panicle inflorescence. Extensive aerenchyma tissues in the cortex permit the rice plant to persist in very poorly drained soils. Ecotypes of rice include indica, japonica and javanica (Smith, 1995).

Potassium (K) has a critical role in plant physiology. In rice, K provides regulatory control over such processes as transpiration, starch synthesis, sucrose translocation, respiration, and lipid synthesis (Tisdale et al., 1985). Proper K nutrition in rice promotes tillering, panicle development, spikelet fertility, plant uptake of N and P, leaf area and leaf longevity, disease resistance, root elongation and thickness, and culm (stem) thickness and strength (Fugiwara, 1965; Ishizuka and Tanaka,1960; Noguchi and Sugawara, 1966).

The effect of the K fertility status of soil on the agronomic performance of rice has been reviewed (DeDatta and Mikkelsen, 1985; Ishizuka, 1965; Mengel et al., 1976; Mengel and Kirkby, 1982; Patnaik and Abichandani, 1970). The interaction of K with N (Mengel et al., 1976), Mg (Mengel and Kirkby, 1982), and with Fe, Mg and Ca (Tanaka and Tadano, 1972) shows that K root uptake patterns are complex and not always easily predictable. Ishizuka (1965) showed that K uptake follows a sigmoidal curve, with the uptake of K paralleling the accumulation of dry matter from emergence to anthesis; after which, K uptake slows dramatically. During seed development, transfers of K from leaf sheaths largely account for the K accumulation in the seed, explaining the often observed decline in K leaf tissue concentrations, particularly after anthesis. Yoshida (1981) and Mikkelsen (1983) provide estimates of critical K levels in rice leaf tissue as a function of plant growth and development.

Phosphorus (P) is of equal importance to plant physiology, being a necessary constituent of ATP, nucleic acids, phospholipids, phosphosugars, and many other important biochemical compounds (Tisdale et al., 1985). The effect of P fertility on the agronomic performance of rice has been reviewed (Davide, 1965; Ishizuka, 1971; Nelson, 1980; Olsen, 1958; Sims and Place, 1968; Terman and Allen, 1970; Thompson et al., 1962). Proper P nutrition in rice increases the leaf number and leaf blade length, increases the number of panicles per plant and the number of seeds per panicle (Nelson, 1980; Teo, Beyrouty et al., 1992). The reduced tillering capacity for rice planted in a P impoverished soil is usually the greatest factor responsible for reduced yields. Flooding rice soils generally moderates the pH towards a neutral condition, thus promoting the soil P availability (Nelson, 1980; Fageria, Zimmermann et al., 1995; Fageria and Baligar, 1999).

Materials and Methods

The study area is the Missouri Rice Research Farm in Dunklin County, Missouri. The region's climate is humid continental, with a mean daily summer temperature of 26[degrees]C (79[degrees]F). The soil is a member of the Crowley series (fine, montmorillonitic, thermic Typic Albaqualfs) that has recently been land graded.

The experimental design was a replicated randomized block design with treatments involving K and P. The K treatment levels were 0 (control) 33 (30), 67 (60), and 100 (90) kg [K.sub.2]O/ha (lbs [K.sub.2]O/acre), whereas the P treatment levels were 0, and 56 (50) kg [P.sub.2][O.sub.5]/ha (lbs [P.sub.2][O.sub.5]/acre). All possible combinations of P and K were performed and each treatment was replicated four times. Plot dimensions were 3.07 by 6.15 m (10 by 20 ft). Soil testing was performed before planting by dividing the study area into two areas and randomly selecting cores, which were then blended to obtain a composite sample for each area. After harvest, each treatment plot was sampled by blending four cores.

The rice variety 'Lamont' was planted in late-May in 1996 and 1997. Phosphorus and K applications consisted of concentrated superphosphate (0-46-0) (monocalcium phosphate) and potash (0-0-60) (KCI) applied surface broadcast immediately after planting. Nitrogen fertilization consisted of 134 kg N/ha (120 lbs. N/acre) of urea applied immediately prior to flood with two 34 kg N/ha (30 lbs N/acre) urea applications at mid-season. Weed control consisted of 7 liters of Stain (proponil)/ha followed by a second application prior to flood establishment.

Tissue analysis occurred in late-June and late-July (1996) and in mid-July and late-August (1997). Tissue samples consisted of 10 recently mature leaves selected from 10 randomly selected plants within each treatment plot. Nitrogen was determined by a C-N analyzer. Calcium, S, 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. Nitrogen, 5, P, K, Ca, and Mg are expressed as percent of dry weight, whereas Fe, Mn, Cu and Zn are expressed as mg / kg-dry weight (ppm). Field measurements involved tiller counts, the number of panicles per row, the number of spikelets per panicle, the percentage of fertile spikelets, seed weight, dry matter accumulation, and yield. In-field counts (tiller counts, the number of panicles per row) consisted of two replications using a 3 meter transect within the row, whereas the number of spikelets per panicle, the percentage of fertile spikelets, seed weight, dry matter accumulation were determined using 10 selected plants with counting-weighing. Tillering was estimated just prior to panicle initiation in 1996 and at harvest in 1997. Additionally, in 1997, the panicle density was estimated at harvest. Harvest (15 Oct 96 and 30 Oct 97) was by plot combine, followed by seed moisture determination. After harvest, each harvested area of each plot was independently measured for length and width. Data analysis involved analysis of variance and regression analysis using routines contained in Quatro-Pro.

Results and Discussion

Soil Analysis: Soil analysis revealed that the test area was strongly deficient in both P and K. Typical P levels were less than 11 kg [P.sub.2][O.sub.5]/ha (10 lbs [P.sub.2][O.sub.5]/acre), whereas K was generally much less than 67 kg [K.sub.2]O/ha (60 lbs K2O/acre), respectively. Normal P levels would be 45 lbs P/acre, whereas normal K levels are 220 + 5 CEC, having units of lbs K/acre (approximately 320 lbs K/acre). Soil [H.sub.p] was 4.9 in 0.5M Ca[Cl.sub.2] and 5.4 in water, each value indicating an acidic soil reaction.

Elemental Analysis of Rice Tissues: Elemental analysis of rice tissues consistently demonstrated that N, S, P, Mg, Ca, Al, B, Na and Mn concentrations were generally not significantly different because of either P or K fertilization in (Table 1). Average mid-July N, S, P, Mg and Ca levels for 1996 were: N (3.6%), S (0.23%), P (0.23%), Mg (0.28%) and Ca (0.38%), whereas average mid-July Fe, Mn, Cu and Zn levels were: Fe (98 mg * kg-1), Mn (860 mg * kg.-1), Cu (5.6 mg * kg-1) and Zn (20.8 mg * kg-1). Average mid-July N, S, P, K, Mg and Ca levels for 1997 were: N (3.5%), S (0.22%), P (0.27%), K (1.45%), Mg (0.26%) and Ca (0.40%), whereas average mid-July Fe, Mn, Cu and Zn levels were: Mn (1511 mg * [kg.sup.-1]) and Cu (12.5 mg * [kg.sup.-1]). In 1996, K fertilization did significantly enhance the mid-July K tissue concentration (Fig. 1). In 1997, Fe and Zn tissue levels were enhanced because of K fertilization (Fig. 2). The elemental concentrations of N, 5, P, K, Mg, and Ca are representative of nutritionally healthy rice (Tisda le et al., 1985). Manganese concentrations are excessive, whereas Zn concentrations are uniformly deficient.

Phosphorus fertilization did reduce Zn tissue concentrations during both sampling periods in 1997 (37.8 versus 31.1 mg [kg.sup.-1] in mid-July and 12.3 versus 9.6 mg [kg.sup.-1] in late-August). All other effects attributed to P were not significant. Because of the lack of P significance, the P treatments on rice yield will not be further discussed.

Agronomic Performance and Yield: Tillering and panicle development are complex responses to the environmental and nutritional status of the study area. The extent of tillering did increase with K fertilization in 1996, but the increase in tillering was not statistically relevant (Table 1). The panicle density in 1997 was significantly increased because of K fertilization (Table 1). Phosphorus fertilization did not significantly influence the panicle density.

Potassium fertilization increased the number of spikelets per panicle in each year (Table 1). Spikelet fertility paralleled total spikelet production and was proportionally greater in 1997, presumably because of more moderate temperatures during anthesis. Phosphorus did not significantly influence panicle development. The rough rice yield was significantly increased because of K fertilization. During both years the application of 67 kg [K.sub.2]O/ha significantly increased rice yields above that of the control and the 33 kg [K.sub.2]O/ha treatment. Phosphorus fertilization did not affect yield.

Regression analysis of exchangeable K (independent variable) with the panicle density or yield (dependent variables) was not meaningful. The coefficients of the independent variable, although positive, were not significantly different from zero. This suggests that the relationships between exchangeable K and either the panicle density or yield were randomly distributed. It is interesting to note that the exchangeable K expression of the K control plots which also received superphosphate were significantly greater than those control K plots which did not receive superphosphate. Zhou and Huang (1995) observed that monoammonium phosphate induced K release from selected Chinese soils. These authors proposed that acidity generation from fertilizer dissolution and the small hydrated radius of the ammonium phosphate permitted the release of K from clay and feldspar. Whether these exchangeable K expressions are a consequence of superphosphate fertilization or simply a result of natural variation may be an important area of future research.

Conclusions and Future Research Needs

Potassium fertilization significantly increased the yield of rice. Yield data suggests that a rate of 67 kg [K.sub.2]O [ha.sup.-1] was superior to a rate of 33 kg [K.sub.2]O [ha.sup.-1]; while a rate of 100 kg [K.sub.2]O [ha.sup.-1] could not be justified. The yield advantage of the 67 kg [K.sub.2]O [ha.sup.-1] rate was attributed to an increase in tillering and spikelet production. Phosphorus fertilization did not significantly increase the rice yield, even though the soil test indicated a need for P.

Future research needs must focus on a reassessment of the K needs of rice and a reappraisal of the standard K soil test levels for rice. Currently, the K needs are adapted from Arkansas and these Arkansas levels were implemented before the dramatic growth of rice culture in the Lower Mississippi River Valley.

(*.) Department of Geosciences, Southeast Missouri State University. Cape Girardeau, MO, 63701. Corresponding author.

Literature Cited

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Fageria, N.K., F.J.P. Zimmermann, and V.C. Baligar. 1995. Lime and phosphorus interactions on growth and nutrient uptake by upland rice, wheat, common bean abd corn in an oxisol. J. Plant Nutr. 18:2519-2532.

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Fujiwara, A. 1965. The specific role of nitrogen, phosphorus, and potassium in the metabolism of the rice plant. P. 93-105. In International Rice Research Institute. The mineral nutrition of the rice plant. John Hopkins Press, Baltimore, Md.

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 Yield components for a K fertility
 trial involving rice.
Treatment Tillers Spikelets / panicle Yield
kg K2O/ha Plant-1 total fertile lbs/a kg/ha
0 4.8a 99a 84a 6620 7410a
33 4.5a 100a 88a 6920 7750a
67 5.1a 104b 83a 7440 8330b
100 5.0a 108c 84a 7660 8580b
0 110a 112a 102a 8398 9405a
33 136b 114b 104b 8522 9545a
67 146b 127b 113b 8911 9980b
100 144b 117b 110b 9041 10125b
[n] Within a column, different letters represent
significant differences (P=0.05%)
[pound] Each number is the mean of four plot samples.
(Treatments involving P fertilizer are omitted)

[Graph omitted]

[Graph omitted]
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Article Details
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Author:Skidmore, Ryan
Publication:Transactions of the Missouri Academy of Science
Article Type:Statistical Data Included
Geographic Code:1U6MS
Date:Jan 1, 1999
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