Yield and Quality Response of Rice Cultivars to Preflood and Late-season Nitrogen

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Jason A. Bond, 1373 Caffey Road, Rice Research Station, Louisiana State University AgCenter, Rayne 70578; and Patrick K. Bollich, 2310 Ben Hur Road, Central Research Station, Louisiana State University AgCenter, Baton Rouge 70820

Abstract

Field research was conducted for 2 years on a silt loam soil near Crowley, LA, and a clay soil near Pioneer, LA, to determine the yield and milling effects of different rates of N fertilizer applied prior to flooding and at the booting growth stage on five long-grain rice cultivars. Rice cultivars included Cheniere, Cocodrie, Cypress, Francis, and Wells. Urea N was broadcast on the soil surface prior to flooding (PFN) at 75 and 150 lb/acre, and these applications were followed at the booting growth stage (BN) with N applied at rates of 0, 34, or 68 lb/acre. Preflood N at the 150 lb/acre rate resulted in 1860 and 980 lb/acre greater rough rice yield than the 75 lb/acre rate at the Crowley and Pioneer locations, respectively. The BN application rate had no effect on any parameter examined. Regardless of BN rate, rough rice yields were equivalent at Pioneer and Crowley when the PFN rate was 150 lb/acre; however, rough rice yield was 12% higher at Pioneer than Crowley when PFN rate was 75 lb/acre. Head rice and total milled rice yield percentages were 10 and 3% greater, respectively, at Pioneer than Crowley when PFN rate was 150 lb/acre. An application of N during the booting growth stage did not improve rice grain yield or quality, and rice quality was maximized following PFN rates that maximized rough rice yield.

Introduction

Nitrogen is one of the most yield-limiting nutrients in lowland rice (Oryza sativa L.) production, and proper N management is essential for improving rice grain yields (7). Rice cultivars commonly grown in the United States require and respond to large amounts of N (1,14). Nitrogen use efficiency in a drill-seeded cultural system is optimized when N is applied in a single preflood application (PFN) under optimum conditions and intensive management (1,12). This single PFN application is made to a dry soil when rice is at the four- to five-leaf stage and before permanent flood establishment (1,2). Multiple, or split, applications may be employed to fertilize tall, lodging-prone cultivars or semidwarf cultivars grown on some clay soils requiring high N rates (14). Split applications are also recommended where management is challenging, i.e., permanent flood cannot be established in 5 days, flood could be lost following PFN application and flooding, or rice water weevil (Lissorhoptrus oryzophilus Kuschel) infestations are probable. If split applications are used, 50 to 65% of the total N requirement is applied immediately prior to permanent flood establishment, and the balance is applied at midseason when rice is at the panicle initiation to panicle differentiation growth stages (1,18).

Nitrogen application rate can influence quality characteristics of rice. Positive relations between N rate and head rice yield were observed by Nangju and De Datta (11) and Seetanum and De Datta (16). Application of N fertilizer during the late reproductive (booting) growth stage (BN) may have an effect on rice grain and milling yield, but this response has not been studied extensively. Although N fertilizer application rate and timings have been thoroughly studied in rice, a tremendous amount of time and resources in rice research are still devoted to N fertilizer management. Furthermore, few published reports are available on the effects of BN applications on rice yield and milling quality. The objective of this research was to evaluate the response of five long-grain rice cultivars to different rates of N fertilizer applied prior to flooding and at the booting growth stage.

Two Locations and Five Rice Cultivars

Experiments to determine the rice response of five rice cultivars to N fertilizer application rates and timings were conducted in 2003 and 2004 at the Louisiana State University AgCenter Rice Research Station near Crowley, Louisiana, and at an on-farm site near Pioneer, LA. Soil at Crowley was a Crowley silt loam soil (fine montmorillinitic, thermic Typic Albaqualf), and soil at Pioneer was a Sharkey clay (very-fine, smectitic, thermic Chromic Epiaquerts). The Crowley silt loam is the predominant soil type in the major rice-growing area of southwest Louisiana, while the Sharkey clay is a representative soil type for the rice-growing area of northeast Louisiana.

The long-grain rice cultivars Cheniere, Cocodrie, Cypress, Francis, and Wells were drill-seeded on 15 April 2003 and 24 March 2004 at Crowley, and 21 April 2003 and 20 April 2004 at Pioneer. A seeding rate of 90 lb/acre was seeded at a depth of 0.75 inch at Pioneer and Crowley. All experiments were drill-seeded using a small-plot grain drill. Standard agronomic and pest management practices were implemented throughout the growing season to maximize yields (10). Individual plots consisted of 12 rows measuring 25 ft in length. At Crowley, P and K were applied based on soil test results at planting at a rate of 30 and 60 lb/acre, respectively. Soil tests indicated that no P or K was required at Pioneer. Plots were flooded to an approximate depth of 3 to 5 inches when rice was at the four- to five-leaf stage at both locations. At maturity, plots were drained approximately 2 weeks before harvest. Rice was harvested with a small-plot combine at a moisture content of approximately 20% using an 18- to 24-inch cutting height. Harvest dates were 19 August 2003 and 4 August 2004 at Crowley, and 8 September in both 2003 and 2004 at Pioneer.

Experiments were arranged in a randomized complete block with a factorial arrangement of five rice cultivars, two PFN rates, and three BN rates with four replications. The five long-grain rice cultivars were drill-seeded as previously described. Cheniere, Cocodrie, and Cypress represent semidwarf rice cultivars, while Francis and Wells are conventional height cultivars. Preflood N was applied at rates of 75 or 150 lb/acre as urea broadcast on the soil surface immediately prior to flood establishment. Booting N was applied at rates of 0, 30, or 60 lb/acre as urea broadcast on the soil surface when approximately 5% of the plants in an individual plot had visible panicles.

Days to 50% heading were determined by calculating the time period from seedling emergence until 50% of rice had visible panicles. Lodging was visually estimated prior to harvest on a scale of one (erect) to nine (prostrate). Mature plant height was recorded prior to harvest. When rice grain reached 18 to 20% moisture content, four row lengths of 3.25 ft were harvested to determine head rice and total milled rice yields. These samples were threshed with an Almaco plot thresher and dried to approximately 12% moisture content. Head rice and total milled rice yields were estimated from 125-g samples of cleaned rough rice. Rough rice was hulled and milled using a laboratory miller for 30 s, and size separated with a no. 12 (4.76 mm) screen. Head rice (unbroken kernels) and total milled rice (broken and unbroken kernels) yield percentages were calculated as mass fractions of the original 125-g sample of rough rice. Rough rice yields were determined from harvesting the remaining plot area with a small-plot combine and adjusting to 12% moisture content.

All data were subjected to the Mixed Procedure (SAS Institute Inc., Cary, NC), with years being used as random-effect parameters testing all possible interactions of location, cultivar, preflood N rate, and BN rate. Years, replications (nested within years), and all possible interactions containing these effects were considered random effects; all other variables (location, cultivar, PFN rate, and BN rate) were considered fixed effects. Considering year as an environmental or random effect permits inferences about treatments to be made over a range of environments (5). A similar statistical approach has been successfully used by other researchers (3, 15). Type III Statistics were used to test all possible fixed effects or interactions between the fixed effects and least square means at P ≤ 0.05 were used for mean separation.

Preflood Nitrogen Gives Large Rice Yield and Quality Response

The preflood 150 lb/acre N rate resulted in the highest rough rice yields (Table 1). Averaged across cultivar and BN rate, rough rice yields were 14 and 30% higher at Pioneer and Crowley, respectively, when the PFN rate was 150 lb/acre. The BN applications had no effect on rough rice yield at Pioneer or Crowley (Table 2). Because the main effect of BN rate and all interactions containing BN rate were not significant, these results corroborate earlier findings (1,18) that yield potential is determined by the PFN rate. Bollich et al. (1) and Wilson et al. (18) observed that rough rice yields of semidwarf cultivars were influenced more by the PFN application than by midseason N applications.

Table 1. Effect of location and PFN application rate on rice yield at Crowley and Pioneer, LA in 2003 and 2004.*

PFN rate (lb/acre)	Rough rice yield (lb/acre)		Head rice yield (%)		Total milled rice yield (%)
PFN rate (lb/acre)	Crowley	Pioneer	Crowley	Pioneer	Crowley	Pioneer
75	6130 c	6870 b	60 b	61 b	71 b	71 b
150	7990 a	7850 a	59 b	65 a	70 c	72 a

* Data averaged over cultivar, BN application rate, and two experiments. Means followed by same letter for each parameter are not significantly different at P ≤ 0.05.

Table 2. Effect of location and BN application rate on rice
yield at Crowley and Pioneer, LA in 2003 and 2004.*

BN rate (lb/acre)	Rough rice yield (lb/acre)
BN rate (lb/acre)	Crowley	Pioneer
0	7100 a	7330 a
30	7190 a	7360 a
60	7190 a	7380 a

* Data averaged over cultivar, PFN application rates, and
two experiments. Means followed by same letter are
not significantly different at P ≤ 0.05.

Regardless of location, cultivar, or BN rate, increasing PFN rate from 75 to 150 lb/acre increased mature plant height 9% (Table 3). Mature plant heights, averaged across PFN and BN rates, were greater at Crowley than Pioneer for all cultivars except Wells, for which mature plant heights were equivalent at both locations (Table 4). The higher PFN rate also delayed the number of days to 50% heading by 3 days (Table 3). In Louisiana, a ratoon-crop harvest (grain harvested from tillers originating on the stubble of a previously-harvested crop) is valuable to a producer’s income because the additional harvest increases total production on a given area with a limited amount of additional input. Delays in main-crop maturity and subsequent harvest could lower the potential for a successful ratoon crop.

Table 3. Effect of PFN application rate on agronomic performance.*

PFN rate (lb/acre)	Days to 50% heading (days)	Mature plant height (inches)
75	83 b	31 b
150	86 a	34 a

* Data averaged over location, cultivar, BN application rate, and two
experiments. Means followed by same letter within a column are not
significantly different at P ≤ 0.05.

Table 4. Effect of location and cultivar on agronomic performance and yield at Crowley and Pioneer, LA in 2003 and 2004.*

Cultivar	Mature plant height (inches)		Rough rice yield (lb/acre)		Head rice (%)
Cultivar	Crowley	Pioneer	Crowley	Pioneer	Crowley	Pioneer
Cheniere	33 c	30 d	7200 bcd	7110 cde	63 b		66 a
Cocodrie	34 bc	31 d	7270 bc	7540 b	62 bc		64 ab
Cypress	34 bc	31 d	6850 de	6700 e	66 a		66 a
Francis	36 a	33 c	7230 bcd	8110 a	52 e		60 cd
Wells	35 ab	34 bc	6740 e	7390 bc	53 e		59 d

* Data averaged over PFN and BN application rates, and two experiments. Means followed by same letter for each parameter are not significantly different at P ≤ 0.05.

Rough rice yields averaged across PFN and BN rates were equivalent at Crowley and Pioneer for Cheniere, Cocodrie, and Cypress (Table 4). Rough rice yields of Wells and Francis were greater at Pioneer than Crowley. Westcott et al. (17) reported 38% higher grain yield for the semidwarf long-grain cultivar ‘Lemont’ grown at St. Joseph (Sharkey clay soil) compared with the Crowley location (Crowley silt loam soil). Rough rice yields of the semidwarf cultivars (Cheniere, Cocodrie, and Cypress) in the current research were not dependent on location or soil since rough rice yields were equivalent at Crowley and Pioneer. However, rough rice yields of the conventional height cultivars Francis and Wells were greater at Pioneer compared with Crowley, indicating that soil and plant type are important considerations for rice cultivar selection.

Regardless of BN rate, rough rice yields were equivalent at Crowley and Pioneer when the PFN rate was 150 lb/acre; however, rough rice yield was 12% higher at Pioneer than Crowley when PFN rate was 75 lb/acre (Table 1). Westcott et al. (17) reported higher grain yield at St. Joseph (Sharkey clay soil) compared with the Crowley location (Crowley silt loam soil) regardless of seeding method (water- or drill-seeded) or N application timing (single or split applications). However, Chen et al. (6) reported that rice grown in 1982 at Beaumont (Beaumont clay) responded more to N than rice grown in 1983 at Eagle Lake (Nada sandy loam), but responses were similar for the two locations in other years. They reported that the Nada sandy loam soil had a high native N supply as indicated by the high control yield (4948 lb/acre) but was responsive to N fertilization as well (1360 lb/acre response from 120 lb of N per acre). The response to PFN rate in the current study may have resulted from the cropping sequences used at the experimental sites. Soybean [Glycine max (L.) Merr] residues have a narrow C:N ratio and a high N content (8). Therefore, soybean residue can contribute significant amounts of N to a rice crop the following year through mineralization. The experimental sites at Crowley were left fallow in the year preceding the experiment, while the experimental site at Pioneer contained soybean in the year preceding the experiment. Differences in rough rice yield at the higher PFN rate may have been minimized by residual N in the soil following soybean at the Pioneer site. Residual N in the soil following soybean at Pioneer may also explain the greater rough rice yield at the lower PFN rate at that site.

The cultivars Cheniere, Francis, and Wells produced 5, 15, and 11% greater head rice yield percentages, respectively, when grown at Pioneer compared with Crowley (Table 4). Norman et al. (13) reported that head rice yield percentage of the semidwarf cultivar Cypress was independent of N fertilizer rate and timing, while head rice yield percentage of the conventional height cultivar LaGrue increased with increasing N fertilizer rate. Results of the current research demonstrate that head rice yield percentages of the semidwarf cultivars Cypress and Cocodrie are also independent of location or soil type since head rice yields for these cultivars were equivalent at Crowley and Pioneer. However, similar to observations for rough rice yield, head rice yield percentages of the conventional height cultivars Francis and Wells were greater at Pioneer compared with Crowley. The increase in head rice yield percentage for the semidwarf Cheniere at Pioneer compared with Crowley was relatively small in relation to those observed for Francis and Wells. The head rice yield percentage response of Cheniere to location was an anomaly considering the responses of the other cultivars.

In contrast to rough rice yield, head rice and total milled rice yield percentages were equivalent at Crowley and Pioneer when the PFN rate was 75 lb/acre (Table 1). Head rice and total milled rice yield percentages were 10 and 3% greater, respectively, at Pioneer than Crowley when PFN rate was 150 lb/acre. Even though differences in total milled rice percentage were detected for the PFN rates at Crowley and Pioneer, these differences were very small and probably of little consequence. At Pioneer, head rice yield percentage improved when the PFN rate was increased from 75 to 150 lb/acre. Increasing the PFN rate did not improve head rice yield percentage at Crowley. Other researchers also observed positive head rice yield percentage responses to N application rates (4,11,16).

Norman et al. (13) reported positive head rice and total milled rice yield percentage responses in LaGrue and Cypress to 40 lb of N per acre applied at the booting growth stage in one of two years. Jongkaewwattana et al. (9) concluded that head rice yield percentage was highest when the N fertilizer rate producing maximum grain yield was used. Results of the current research indicated that N fertilizer applied at booting had no effect on head rice and total milled rice yield percentages. Furthermore, rough rice yields were not influenced by N fertilizer applied during booting, and the N fertilizer rate producing the maximum grain yield also produced the highest head rice yield percentage (Table 1).

These results indicate PFN rate is important for semidwarf and conventional height rice cultivars. At Pioneer, supplying 150 lb of N per acre in a preflood application improved rough rice yield, head rice, and total milled rice yield percentages compared with supplying only 75 lb of N per acre. However, at Crowley, increasing the PFN rate only improved rough rice yield and total milled rice yield percentage. An application of N during the booting growth stage did not improve rice grain yield or quality, and rice quality was maximized following PFN rates that maximized rough rice yield. In the area of rice nutrition, early-season management decisions, including site selection, cultivar selection, and PFN management are critical for high yields, and deficiencies in these areas cannot be overcome by N applications during reproductive growth stages.

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