The Effect of Phosphorus Fertilizer Rate and Application Time on Rice Growth and Yield

Transcription

1 RICE CULTURE The Effect of Phosphorus Fertilizer Rate and Application Time on Rice Growth and Yield N.A. Slaton, J. McGee, R.J. Norman, R.E. DeLong, and C.E. Wilson, Jr. ABSTRACT Three studies have been conducted since 2001 to examine rice growth, nutrition, and yield response to phosphorus (P) application rate and time. The three sites represent high-ph silt loam soils (>7.5) with a range of Mehlich 3-extractable P (8 to 41 mg P/ kg). The objective of this research was to measure rice biomass and tissue-p concentration during the growing season and rice grain yield response as affected by P- fertilizer application time and rate. In 2002, P fertilizer was applied at rates of 0, 25, 50, and 100 lb P 2 O 5 /acre before rice emergence, preflood, midseason, and at the late boot stage in a study conducted in a Cross County, AR, rice field and at the Pine Tree Branch Experiment Station (PTBS). Significant yield responses were only observed in the 2001 study (Slaton et al., 2002b). However, tissue-p concentrations have tended to increase as P-fertilizer application during vegetative growth was delayed from the time of seeding until the 5-leaf stage at two of three sites. This provides solid evidence that P application time is critical for efficient plant uptake of applied P fertilizer on P-deficient soils. Until soil chemical properties are accurately correlated with tissue-p concentrations, growers should continue to apply P based on current soil-test recommendations at the time that best suits their crop management system. INTRODUCTION Phosphorus deficiency of rice seldom occurs in the dry-seeded delayed-flood management system used to produce rice in Arkansas. However, when P deficiency does occur it dramatically reduces early rice growth, delays development, and results in significant yield losses. We have previously reported that the time of P fertilizer 321

2 AAES Research Series 504 application affects rice response to P fertilization (Slaton et al., 2002a, 2002b). Last year we documented that rice uptake of P was more efficient when P fertilizer was applied before flooding rather than before rice emergence on some soils (Slaton et al., 2002a). Two more years of data are needed to support the observations made in 2001 characterizing the seasonal trends of P uptake as affected by P application time. The objectives of this research were to i) measure rice biomass and P uptake during the growing season and ii) measure rice grain yield response as affected by P fertilizer application time and rate. MATERIALS AND METHODS A study was established on the Darryl Schlenker farm near Hickory Ridge, AR, (Cross County, AR) and on the PTBS located near Colt, AR in The soils at the PTBS and Cross County were mapped as a Calhoun silt loam and a DeWitt-Hillemann complex, respectively. Both sites represent soils with high ph but quite different Mehlich 3-extractable P (Table 1). The Cross County field was seeded with the medium-grain rice cultivar Bengal at a rate of 120 lb/acre on 23 April The individual plots were 8 ft wide, consisting of 14 rows with 7-in. drill spacing, and were 16 ft long. At the PTBS, the long-grain cultivar Wells was seeded at a rate of 100 lb/acre on 16 April 2002 in plots that were 9 rows wide with 7-in. drill spacings and 16 ft long. At each site a composite soil sample was taken from the untreated control plot and four other plots selected at random (2 composite samples per replication). Each composite sample consisted of eight 2 cm wide 10-cm (4 in.) deep soil cores. Soil samples were oven-dried, crushed, and placed through a 2-mm sieve. Available soil nutrients (Ca, Mg, Na, K, Fe, Mn, Cu, Zn, and P) were determined by extraction according to the Mehlich 3 procedure (Mehlich, 1984). Selected soil chemical properties, averaged across the eight or ten composite samples, of the study site are listed in Table 1. Based on current University of Arkansas fertilizer recommendations, 60 lb P 2 O 5 /acre was recommended for the PTBS site and 0 lb P 2 O 5 /acre on the Cross County site. Potassium (100 lb KCl/acre) and Zn (1 lb foliar-applied Zn/acre) fertilizers were applied at each location to ensure these nutrients would not be yield-limiting factors. Phosphorus fertilizer (triple super phosphate, ) was applied at rates of 25, 50, and 100 lb P 2 O 5 /acre. Phosphorus fertilizer was broadcast-applied before emergence 1 d after seeding (DAS) (preemergence, PE); 37 DAS at the 5-leaf stage (preflood, PF); 64 DAS at 1.25-in. internode elongation (panicle initiation, PI); and 91 DAS after the flag leaf was fully emerged (late boot, LB). All P fertilizer rates and times of application were compared to an untreated control (NONE or 0 lb P 2 O 5 /acre). The first two P application timings, PE and PF, were made to dry or moist soil conditions. At PI and LB, P applications were made into the flood water. With the exception of P fertilization, the plot management with respect to fertilization, irrigation, and pest control was similar to guidelines recommended by the cooperative extension service for the dry-seeded delayed-flood rice cultural system (Slaton, 2001). 322

3 B.R. Wells Rice Research Studies 2002 Plant samples were taken at selected intervals, approximately every 14 d beginning after the first flooding, during the growing season. Sampling dates are expressed as the number of days after seeding (DAS). Whole-plant biomass from a 3-ft row section of the second inside row was removed at the soil surface. At each sample date, only the treatments that had received P fertilizer and the untreated control were sampled. The untreated control and all P rates of the PE and PF P application times were sampled at all sample dates during the season. All P application times and rates were sampled at 100% heading and maturity. At maturity (the final sample date) panicles were removed at the top node from the straw to estimate partitioning of plant P. Before P-fertilizer application at the PI and LB stages, biomass, tissue-p concentration, and P uptake of these P treatments were assumed similar to those of the untreated control. Plant samples were dried in a forced-draft oven at 60 C until a constant moisture was reached, weighed, ground to pass through a 1.0-mm sieve, and a 0.25 g sub-sample was digested with concentrated HNO 3 and 30% H 2 O 2 as described by Jones and Case (1990). The digests were analyzed for Ca, Mg, Na, K, Fe, Mn, Zn, Cu, P, and S by inductively-coupled atomic-plasma spectroscopy. Total P uptake by rice straw and grain were calculated by multiplying the straw or grain-p concentration by straw or panicle weights. At maturity, a 28-ft 2 area from the middle four rows of each plot was harvested with a small-plot combine for grain yield. Grain moisture ranged from 16 to 20% at harvest. Grain moisture was adjusted to a uniform moisture content of 12% for statistical analysis. Crop removal of P was calculated by multiplying the harvested grain yield by panicle-p concentration. The experiments were arranged in a 3 (P application rate) 4 (time of application) randomized complete block factorial design and were compared to an untreated control. Each treatment was replicated four times at Cross County and five times at the PTBS. Sample time was not statistically evaluated. Locations were analyzed separately. For biomass, straw-p concentration, and P uptake only the P-application times sampled were included in the statistical analysis. Mean separations were performed by Fisher s Protected Least Significant Difference method at a significance level of RESULTS AND DISCUSSION Total Dry Matter and Grain Yield Rice grain yield was not affected by P-application rate or time or the interaction between P rate and application time at either location. Yield means for the main effects are listed in Table 2. Although rice grain yields were not increased or decreased in either of the 2002 studies, the data provide valuable information for the correlation of Mehlich 3 P and other soil chemical properties with rice yield and other growth measurements. We have not measured significant rice yield responses to P fertilization at the PTBS during the past 10 years, so the lack of yield response in this study was not surprising. Although the PTBS site had high ph and low Mehlich 3-extractable P, the soil Ca is relatively lower than most grower fields (Table 1) and suggests that a variable, like soil Ca, other than soil ph may be better correlated for use with Mehlich 3 P for 323

4 AAES Research Series 504 accurate prediction of rice response to P fertilization. Total dry-matter production was not significantly affected by the time of P application at any sample time during the season at the PTBS (data not shown). Time of application significantly affected straw production at maturity (data not shown) with the unfertilized control producing the greatest straw weight. The rate of P application, time of P application, and their interaction did not significantly affect rice yield (Table 2) or dry-matter production (data not shown) at any sample time at the Cross County site. In contrast to the soil at the PTBS, the Cross County site also had high ph but had a very high soil Ca and relatively high Mehlich 3 P (Table 1). Thus, the lack of yield response at this site suggests that Mehlich 3 P may be useful in correlating rice response to P fertilization. Tissue-P Concentration and Content Tissue-P concentrations across time from the Cross County site shows that soil P availability was never limiting on this soil since tissue-p concentrations were high (> 0.25%) and relatively constant for all treatments across all sample dates (data not shown). Total aboveground P content or uptake were not affected by the main effects or their interaction at any sample date. At the PTBS, the time of P application significantly affected tissue-p concentration 48 and 64 DAS (Table 3). Phosphorus fertilizer applications made at PE and PF significantly increased tissue-p concentration above that of the unfertilized control at 48 DAS, but after 48 DAS tissue concentrations for the PE and PF applications were statistically similar. At 64 DAS, only P applied PF resulted in significantly higher tissue P concentrations than the unfertilized control. Tissue-P concentrations at the first two sample dates show that tissue P was low (< 0.20%) but not deficient to the point of limiting grain yield and rice growth. By 77 DAS, tissue-p concentrations were >0.25%, which is the concentration that most rice reaches and maintains by the initiation of reproductive growth on Arkansas soils. The increase in tissue-p concentration during rapid vegetative growth indicates that P availability gradually increased as timing of flooding increased until finally soil-p availability was plentiful for the duration of the season. Tissue-P concentration also increased significantly as P application rate increased at 48 DAS and showed a trend to increase at 64 DAS (Table 4). Phosphorus rate did not affect tissue-p concentration after 64 DAS (reproductive growth), which has also been observed in previous studies. Although total aboveground P content or uptake were not affected by the main effects or their interaction, a trend for increased P uptake with P application occurred (data not shown). SIGNIFICANCE OF FINDINGS 324

5 B.R. Wells Rice Research Studies 2002 Three studies have been conducted since 2001 to examine rice growth, nutrition, and yield response to P-application rate and time. The three sites represent high-ph silt loam soils (>7.5) with a range (8 to 41 mg P/kg) of Mehlich 3-extractable P (PTBS-2002 = low, Cross County = medium, and Cross County = high). Significant growth and yield responses were observed only in the 2001 study (Slaton et al., 2002b). However, tissue-p concentrations have tended to increase as the time of P-fertilizer application during vegetative growth was delayed in two of the three sites. This provides solid evidence that P-application time is critical for efficient plant uptake of applied P fertilizer on P-deficient soils. The data clearly demonstrate that a rather complex (i.e., multiple soil-chemical properties) recommendation will be needed to accurately predict the soils where P fertilization is required to optimize plant growth and yield since plant responses are not fully explained with just Mehlich 3-extractable P and soil ph at these study sites. The most consistent plant-growth variable (other than yield) that may show promise to correlate and eventually calibrate rice response to P fertilization is tissue-p concentration during early vegetative growth. When plant tissue-p concentration is low (< % P), a positive growth and yield response is more likely to occur than when tissue-p concentrations are high. The information from these studies will be most useful when rice response to P fertilization can be predicted more accurately since efficient plant uptake will be critical under these situations. These data will also serve as valuable data points in the correlation process. Until soilchemical properties are accurately correlated with tissue-p concentrations, growers should continue to apply P based on current soil test recommendations at the time that best suits their crop management system. LITERATURE CITED Jones, J.B. and V.W. Case Sampling, handling, and analyzing plant tissue samples. pp In: R.L. Westerman (ed.). Soil testing and plant analysis. 3 rd ed. SSSA Book Series 3. SSSA, Madison, WI. Mehlich, A Mehlich 3 soil test extractant: A modification of Mehlich 2 extractant. Commun. Soil Sci. Plant Anal. 15: Slaton, N.A Rice production handbook. Misc. Publ. No University of Arkansas Cooperative Extension Service, University of Arkansas. Little Rock, AR. Slaton, N.A., J. McGee, R.J. Norman, R.E. DeLong, and C.E. Wilson, Jr. 2002a. The effect of phosphorus fertilizer rate and application time on seasonal phosphorus uptake by rice. In: R.J. Norman and J.-F. Meullenet (eds.). B.R. Wells Rice Research Studies University of Arkansas Agricultural Experiment Station Research Series 495: Fayetteville. Slaton, N.A., C.E. Wilson, Jr., S. Ntamatungiro, and R.J. Norman. 2002b. Rice response to phosphorus application timing. Agron. J. 94:

6 AAES Research Series 504 Table 1. Selected soil chemical properties of two phosphorus-rate and time-of- application studies conducted in Cross County and at the Pine Tree Branch Experiment Station (PTBS) during Soil test data for 2001 listed in Slaton et al. (2002a). Soil Mehlich 3-extractable nutrients z Location ph P K Ca Mg Na S Fe Mn Zn Cu (mg kg -1 ) Cross Co PTBS y z y Values are the average of 8 or 10 composite soil samples. PTBS = Pine Tree Branch Experiment Station. Table 2. Effect of P-fertilizer application time and rate on rice grain yield at two locations in P application Grain yield P application Grain yield time z PTBS y Cross Co. rate x PTBS Cross Co (lb/acre) (lb P 2 O 5 /acre) (lb/acre) None Preemergence Preflood Midseason Late boot LSD (0.05) NS NS LSD(0.05) NS NS P-value P-value C.V., % C.V., % z y x Averaged across application rates. PTBS = Pine Tree Branch Experiment Station. Averaged across application times. 326

7 B.R. Wells Rice Research Studies 2002 Table 3. The effect of P fertilizer time of application, averaged across rates of application, on rice tissue-p concentration during the growing season at the Pine Tree Branch Experiment Station during P application Whole-plant tissue-p concentration by sample date time z 48 DAS y 64 DAS 77 DAS 91 DAS 106 DAS Mat-straw Mat-panicles (% P) None Preemergence Preflood Midseason Late boot LSD (0.05) NS x NS NS NS P-value C.V., % z Averaged across application rates. y DAS = days after seeding. 327

8 Table 4. The effect of P-fertilizer application rate, averaged across times of application, on rice tissue-p concentration during the growing season at the Pine Tree Branch Experiment Station during P application Whole-plant tissue-p concentration by sample date rate 48 DAS z,y 64 DAS y 77 DAS x 91 DAS x 106 DAS w Mat-straw w Mat-panicles w (lb P 2 O 5 /acre) (% P) LSD (0.05) NS v NS NS NS NS NS P-value C.V., % z DAS = days after seeding. y Averaged across the preemergence and preflood application times. x Averaged across the preemergence, preflood, and midseason application times. w Averaged across the preemergence, preflood, midseason, and late boot stage application times. v NS = not signficant. 328