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Production Papers

Grain Yield and Milling Quality Response of Two Rice Cultivars to Top-Dress Nitrogen Application Timings

^a Delta Research and Extension Center, Mississippi State Univ., P.O. Box 197, Stoneville, MS 38776
^b Dep. of Agric. Information Science and Education, Mississippi State Univ., 130 Lloyd Ricks, Mississippi State, MS 39762

^* Corresponding author (twalker{at}drec.msstate.edu)

Received for publication November 9, 2005.

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY REFERENCES

 
Combinations of two vegetative N application schemes (single pre-flood [SPF]) and two-way split [2WS]) and five top-dress (TD) N timings (internode elongation [IE], IE+7, 14, 21, and 28 d) were tested for ‘Cocodrie’ and ‘Wells’ rice. When averaged across TD timings, the average grain yield for Cocodrie was 9142 kg ha^–1 when the SPF scheme was used, compared with 8736 kg ha^–1 for the 2WS scheme. Whole and total milled rice percentage showed a quadratic response to TD timing and was greatest when the TD application was made at IE+28 d for Cocodrie; however, only the early vegetative N application scheme affected the net return, which, when averaged across TD timings, was $75 ha^–1 greater when the SPF scheme was used. When N was top-dressed at the IE timing, whole milled rice was 52.9% with the SPF scheme, compared with 49.8% with the 2WS scheme. In addition, where the SPF scheme was used, whole milled rice responded quadratically to TD timing compared with linearly when the 2WS scheme was used. Sensitivity analyses indicated that at three N prices ($0.16, $0.33, and $0.48 kg^–1), the relative difference in net returns among treatment combinations were not changed. Rice grain yields for semi-dwarf cultivars respond more favorably to a higher percentage of the total N being applied pre-flood. Growers should implement N fertilizer practices that produce the highest economic grain yield, which for Cocodrie is to use the SPF vegetative N application scheme regardless of the TD N timing.

Abbreviations: DREC, Mississippi State University Delta Research and Extension Center • IE, internode elongation • SPF, single pre-flood • TD, top-dress • 2WS, two-way split

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY REFERENCES

 
IN midsouthern USA rice production, the amount of N and the incidence of application are greater than any other nutrient (Norman et al., 2003). Rate and timing of N are critical for optimum rice grain yield. Nitrogen increases plant height, panicle number, leaf size, spikelet number, and number of filled spikelets (Dobermann and Fairhurst, 2000), ultimately determining the yield potential of a rice plant. Panicle number is influenced by the number of tillers that develop during the vegetative stage, whereas spikelet number and number of filled spikelets are determined in the reproductive stage (DeDatta, 1981). Jones and Snyder (1987) and Counce (1987) have documented the compensatory relationship where the number of panicles and the number of filled spikelets are often inversely related. Fageria and Baligar (1999) also found this to be true in Brazil.

No suitable soil test method has been established and implemented for determining the N-supplying capacity for soils used to produce rice (Dobermann and Fairhurst, 2000). Instead, numerous N rate and application timing studies have been and continually are conducted on experiment stations and farms to determine N recommendations for the various cultivars that are grown in the rice-producing states.

Most of the rice in Mississippi is produced in a dry-seeded, delayed-flood cultural system in which the permanent flood is not established until the rice is 15 to 20 cm tall. In the southern USA, optimum N fertilizer use efficiency has been achieved by applying at least 50% of the total N pre-flood (PF) and applying the remaining N within the interval beginning with internode elongation (IE) to 10 d after IE of 1.25 cm (Brandon et al., 1982; Mengel and Wilson, 1988; Wilson et al., 1989; Wilson et al., 1998). However, recent work in Arkansas has shown that some new cultivars produce yields that are comparable, and sometimes greater, when a single pre-flood application is made as opposed to a two- or three-way split of the total applied N (Norman et al., 2000a).

Nitrogen uptake and grain response for conventional and semi-dwarf cultivars produced in the southern USA have been thoroughly documented in recent years (Bollich et al., 1994; Bufogle et al., 1997; Norman et al., 1992; Wilson et al., 1989); however, most of the literature for rice grown in the southern USA is limited to pre-plant, pre-flood, and early reproductive applications of N. Bollich et al. (1994) and Wilson et al. (1998) reported that semi-dwarf rice grain yields were affected largely by the PF N application and minimally by IE N applications. Wilson et al. (1998) also observed that the proper rate of PF N increased the uptake efficiency of N fertilizer top-dressed during the early reproductive stages of growth.

Data published from rice-growing regions outside the USA have reported top-dress (TD) applications of N during the latter stages of reproductive growth, which include the boot and early heading stages, have increased rough and whole-grain rice yield (Perez et al., 1996; Wopereis-Pura et al., 2002). Although hybrid rice is grown on large hectarage in Asia (Yuan, 2004; Food and Agriculture Organization, 2004), its adoption in the USA is in its infancy. In studies conducted in Mississippi, rice hybrids often benefit in rough and whole grain rice yield when N is top-dressed at the panicle emergence (early heading) growth stage (Walker, 2005).

Cocodrie, a semi-dwarf, long-grain cultivar (Louisiana State University, 2005), and Wells, a short-stature, long-grain cultivar (Louisiana State University, 2005), were planted to 68% and 5% of the hectarage in Mississippi, respectively, in 2003 and 2004 (Kanter et al., 2004, 2005). Although Wells is not a popular cultivar in Mississippi, it was planted on approximately 33% of the hectarage in the southern USA in 2003, whereas Cocodrie was planted on approximately 36% of the hectarage (Kanter et al., 2004; Louisiana State University, 2004; Texas A&M University, 2004; University of Arkansas, 2004; University of Missouri, 2004). Because there are minimal data showing the response of currently grown rice cultivars to heading applications of N, an experiment was conducted to evaluate TD N timings for the cultivars Cocodrie and Wells. The objectives of this study were (i) to determine the grain yield and milling yield of two early vegetative N application schemes and five TD N timings and (ii) to determine the most economical N application program with respect to N cost, application cost, grain yield, and milling premiums or discounts.

	MATERIALS AND METHODS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY REFERENCES

 
Agronomics
Separate experiments to determine the grain yield and milling quality response of two rice cultivars to different N application schemes were conducted in 2003 on a producer's field (Richard) near Greenville, MS, and in 2004 and 2005 at the Mississippi State University Delta Research and Extension Center (DREC) near Stoneville, MS. The soil at Richard and at DREC was Sharkey clay (very-fine, smectitic, thermic Chromic Epiaquerts). Soil pH (1:1 water) for Richard, DREC04, and DREC05 was 7.0, 8.0, and 8.0, respectively, and contained 15, 22, and 24 g kg^–1 organic matter, respectively.

The experiment sites were in 1:2 rice and soybean [Glycine max (L.) Merr.] rotation. Field preparation each site year consisted of fall disking and two passes in opposite directions with a triple K equipped with rolling baskets and S-tine harrows set to operate at a 6-cm depth. Experiment sites were left fallow during the winter of each year. Emerged vegetation was controlled using glyphosate [N-(phosphonomethyl) glycine] at 840 g ae ha^–1 4 to 5 wk before seeding. Wells and Cocodrie rice were planted on 6 May 2003, 16 Apr. 2004, and 4 May 2005 and emerged on 21 May 2003, 25 Apr. 2004, and 11 May 2005, respectively. The response of these two cultivars to vegetative N application scheme and TD timing were tested in separate experiments, but experiments were conducted concurrently and adjacent to each other. At Richard and DREC04, a custom-manufactured small plot drill equipped with Sunflower (Sunflower Manufacturing, Beloit, KS) double-disk openers was used to plant eight rows spaced 20 cm apart. At DREC05, a modified Great Plains 1520 (Great Plains Manufacturing, Salina, KS) with double disk openers was used to plant eight rows spaced 20 cm apart. Both drills were calibrated to deliver 430 seeds m^–2. After emergence and before flooding, 1.3 m alleys were created between replications using a Bush Hog RTS 50 (Bush Hog, L.L.C., Selma, AL) roto-tiller leaving plots that were 4.9 m in length. Immediately after planting, clomazone [2-(2-chlorophenyl) methyl-4,4-dimethyl-3-isoxazolidinone] at 560 g ai ha^–1 plus quinclorac (3,7-dichloro-8-quinolinecarboxylic acid) at 560 g ai ha^–1 was applied to provide grass and broadleaf weed control. Before flooding, propanil [N-(3,4-dichlorophenyl)propanamide] at 3.4 kg ai ha^–1 plus halosulfuron-methyl[3-chloro-5-[[[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]-1-methyl-1H-pyrazole-4-carboxylicacid] at 56 g ai ha^–1 was applied to maintain weed control. Surface irrigation occurred within 3 d after seeding and at the 3- to 4-leaf rice stage at each experimental site. The Richard site was treated with lambda cyhalothrin [1(S*), 3(Z)]-(±)-cyano-(3-phenoxyphenyl)methyl-3-(2-chloro-3,3,3-trifluoro-1-propenyl)-2,2-dimethylcyclopropanecarboxylate at 36 g ai ha^–1 1 d after permanent flood establishment, whereas DREC04 and DREC05 were planted with seed treated with fipronil [5-amino-1-(2,6-dichloro-4-(trifluoromethyl)phenyl)-4-((1,R,S))-trifluromethyl) sulfinyl)-1-H-pyrazole-3-carbonitrile] at 56 g ai ha^–1 for control of rice water weevil (Lissorhoptrus oryzophilus). A permanent flood was achieved on 19 Jun. 2003, 26 May 2004, and 8 Jun. 2005 for Richard, DREC04, and DREC05, respectively, which corresponded to the 5- to 6-leaf rice growth stage. Standard agronomic and pest management practices were used during the growing season to optimize rice grain yield (Miller and Street, 2000).

The experiment design for all site years was an RCB with four replications. The treatment structure for each site year was a factorial that consisted of two levels vegetative N and five levels of TD N (Table 1). All levels of TD N were applied in the reproductive growth stage. Levels of vegetative N included a single application (single pre-flood [SPF]) of 153 kg N ha^–1 applied to rice within 2 d of permanent flood establishment and a split application (two-way split [2WS]), whereby 101 kg N ha^–1 was applied within 2 d of permanent flood establishment and the balance of 52 kg N ha^–1 was applied 7 d after permanent flood establishment. The five levels of TD N consisted of 52 kg N ha^–1 applied at the beginning of IE and 7, 14, 21, or 28 d after IE, which corresponded to 21, 28, 35, 42, and 49 d after permanent flood establishment. Pre-flood N treatments were weighed individually and applied to dry soil with a custom manufactured self-propelled fertilizer distributor equipped with a Hege belted cone delivery system (Wintersteiger, Salt Lake City, UT) and a zero-max adjustable drive (Zero-Max, Plymouth, MN). Top-dress N applications were weighed and broadcasted by hand into the flood. Urea (46% N) was the N source for all applications.

Economics
Estimates of expenses and returns were developed for each experimental unit. The Mississippi State Budget Generator (MSBG) (Laughlin and Spurlock, 2003), a program used to calculate the Mississippi State University and other universities' annual enterprise planning budgets, was used to estimate expenses. Many expenses are associated with rice production; however, for this analysis, only expenses incurred with N fertilizer treatments were considered; all other expenses are assumed constant across experimental units. All N was valued at $0.33 kg^–1, which was based on 2005 urea prices. A $7.59 ha^–1 expense was calculated for ground application of N and was charged to each experimental unit for the pre-flood N application. This calculation was based on the assumption that a 180-HP tractor and a 5-ton spreader buggy were used. Based on the MSBG, the charge for aerial application costs were $0.109 kg^–1 of fertilizer product. For treatments containing the 2WS application method, 226 kg urea ha^–1 was applied by air and encompassed an aerial application expense of $24.64 ha^–1, whereas treatments containing the SPF application method required 113 kg urea ha^–1 applied by air and encompassed an application expense of $12.32 ha^–1.

The value kg^–1 of rice for each experimental unit was calculated based on the USDA loan rate of $0.047 kg^–1 for whole grain and $0.024 kg^–1 for broken grain. This is equivalent to $0.032 kg^–1 for 55% whole milled rice and 70% total milled rice, which is considered the base milling grade. Average gross returns per experimental unit were calculated by multiplying value kg^–1 by grain yield. A net return was calculated for each experimental unit by subtracting the expenses incurred due to N treatments from the gross return. Additionally, N prices were allowed to vary over three selected prices to determine the sensitivity of treatments to varying N price levels. Prices were chosen based on previous, current, and possible future N prices.

Statistics
Grain yield, milling quality, and net return data were combined over site years for ANOVA and tested for main effects and interactions using a mixed model approach (SAS Institute, 2003). Variances were allowed or not allowed to vary across years for all parameters by selecting the best fit model using Akaike's Information Criterion (Littell et al., 1996). Vegetative N application scheme and TD timing were considered fixed effects. Site year, replications, and any interactions between these factors were considered random effects as suggested by Carmer et al. (1989) and were included in the ANOVA so that broader inferences could be made concerning treatment effects. Orthogonal contrasts were performed using the SAS procedures to evaluate possible linear or quadratic trends with TD timing. Each cultivar was analyzed separately. An interaction among vegetative N application scheme and TD timing occurred for whole milled rice in Wells. The slice option in SAS (SAS Institute, 2003) was used to determine the levels of simple effects that contributed to the interaction. Means were separated using Fisher's LSD, and a significance level of 0.05 was used for statistical tests.

	RESULTS AND DISCUSSION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY REFERENCES

 
Agronomics
For Cocodrie, vegetative N application scheme affected grain yields, and TD timing affected the percent of whole and total milled rice (Table 2). Grain yields were greater when the SPF method was used compared with the 2WS method. Whole milled and total milled rice showed a quadratic response to TD timing. Both milling quality parameters decreased with increasing time after IE until IE+28. Twenty-eight days after the beginning of IE corresponds to the late boot growth stage, which is approximately the time just before the panicle emerges from the sheath. Researchers have reported that semi-dwarf cultivars produced in the midsouthern USA have produced yields equal to and/or greater when 75 to 100% of the total N is applied PF (Mengel and Wilson, 1988; Norman et al., 2000a; Wilson et al., 1998; Slaton et al., 2003). For the cultivar Wells, grain and total milling were not affected by the main effects or interactions among the main effects (Table 2); however, an interaction among the vegetative N application scheme and TD timing was observed for whole milled rice (Table 3). Tests of sliced effects indicated that whole milled rice when measured at the IE TD timing was different between the vegetative N application scheme. When N was top-dressed at IE, whole milled rice was 3.1% greater for the SPF scheme compared with 2WS (Table 3). Within the SPF scheme, whole milled rice responded quadratically to TD timing where the percentages were highest at the IE and IE+28 d timings. However, within the 2WS application scheme, whole milled rice responded linearly to TD timing and produced the greatest percentage at IE+28 d.

Average milling yields for Cocodrie were within the range reported by Linscombe et al. (2000); however, the whole milled rice percentages for Wells reported by Moldenhauer (2001) were approximately 10% greater than what was measured in this study. Based on Moldenhauer (2001) and Linscombe et al. (2000), the genetic potential for whole milled rice for Cocodrie and Wells are similar. Grain weights for Cocodrie and Wells are also similar (Linscombe et al., 2000; Moldenhauer, 2001; Kanter et al., 2006); however, Wells produces a longer, narrower grain compared with Cocodrie's shorter, wider grain (Linscombe et al., 2000; Moldenhauer, 2001). It can be implied from these data that greater fissuring could have been caused in Wells because of the grain shape. Furthermore, TD N timings did not allow Wells rice to overcome the fissuring that occurred in these studies. The data seem to suggest that whole milled rice for cultivars that have a smaller length to width ratio may be affected more by the timing of TD N application. Further investigation is needed to verify this hypothesis.

Economics
For the cultivar Cocodrie, net return was affected only by the vegetative N application scheme. When averaged across TD timings, a $75.34 ha^–1 greater net return was obtained with the SPF N application scheme (Table 2). It can be concluded from these results that the increased value kg^–1 that resulted from increased milling yield at the IE+28 TD timing was not substantial enough to affect the net return. Net return for Wells was not affected by the vegetative N application scheme, TD timing, or an interaction among the two (Table 2). Nitrogen has recently experienced significant price increases. The results in Table 2 were based on average N prices for the 2005 growing season; however, N prices have been volatile in recent years. It is uncertain whether prices will return to previous levels or continue to increase. Table 4 shows the net returns for the data summarized in Table 2 at three selected prices ($0.165, $0.331, and $0.496 kg^–1). The lower and higher prices are representative of previous and potential future prices, respectively. Relative differences were not changed by altering N prices over the selected range (Table 4).

	SUMMARY

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY REFERENCES

	ACKNOWLEDGMENTS

 
This research was funded in part by the Mississippi Rice Promotion Board. We thank Mr. Scott Lanford for providing technical assistance.

	NOTES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY REFERENCES

 
Contribution of the Mississippi Agric. and For. Exp. Stn. Publication J-10834. This research was funded in part by the Mississippi Rice Promotion Board.

	REFERENCES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY REFERENCES

 

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