Published online 26 June 2007
Published in Agron J 99:1143-1150 (2007)
DOI: 10.2134/agronj2006.0298
© 2007 American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA
Rice
Planting Date Affects Grain and Milling Yields of Water-Seeded Clearfield Rice
X. Y. Sha* and
S. D. Linscombe
Rice Research Station, Louisiana State Univ. Agricultural Center, Crowley, LA 70578
* Corresponding author (xsha{at}agcenter.lsu.edu)
Received for publication October 25, 2006.
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ABSTRACT
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Planting date affects rice grain and milling yields. However, no such research has been conducted on the imidazolinone-tolerant Clearfield (BASF Corporation, Ludwigshafen, Germany) rice, which has been rapidly adopted in the southern USA since 2003. To investigate the planting date effects on rice grain and milling yields, a field test involving both Clearfield and conventional rice cultivars was water-seeded at 2-wk intervals from late February to early July from 2003–2005 in Crowley, LA. Our results indicated that both Clearfield and conventional rice planted between 1 April and mid April produced the highest grain yield. Grain yield gradually declined at the two subsequent May planting dates, with dramatic reductions occurring thereafter. The pooled grain yields across years and cultivars were 7.94 Mg ha–1 for two April plantings, followed by 6.76 and 6.28 Mg ha–1 for early and mid May plantings, respectively. However, the two delayed plantings in early June and late June or early July produced the lowest grain yields of 4.51 and 3.64 Mg ha–1, respectively. The highest head rice yield of 652 g kg–1 was observed at mid-April planting dates, followed by 638 g kg–1 at mid-May planting dates. However, rice seeded immediately after those two dates had the lowest head rice yields of 606 and 597 g kg–1, respectively, which might be related to the low seedling stand and/or hot and dry weather during late August and early September when the rice headed. Therefore, water seeding of both Clearfield and conventional rice should occur from 1 April to mid-April in southwest Louisiana to maximize both grain and milling yields.
Abbreviations: LSU RRS, Louisiana State University AgCenter's Rice Research Station
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INTRODUCTION
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PLANTING RICE in the optimum period of time is critical to achieve high grain yield and good milling quality. However, optimum rice planting dates are regional and vary with location and genotypes (Bruns and Abbas, 2006; Sha and Linscombe, 2005). In the USA, it was recommended that rice should not be planted until the average air and/or soil temperature reaches 15°C (Street and Bollich, 2003). Rice seeded before the window of optimum dates usually has slow germination and emergence, poor stand establishment, and increased damages from soilborne seedling diseases under cold conditions, as well as lost seeds to birds (black birds, ducks, and geese) that are more concentrated in the early season (Linscombe et al., 1999). Planting rice after the optimum dates can result in higher disease and insect incidence, tropical storm-related lodging, and possible cold damage during heading and the grain filling period resulting in low yields (Groth and Lee, 2003; Thompson et al., 1994).
The introduction of Clearfield rice in 2002 has revolutionized southern USA rice production. Combined with imazethapyr herbicide, Clearfield rice allows for the first time ever selective control of noxious red rice in a commercial rice field (Croughan, 2003). In the first 4 yr since its official release, Clearfield rice has been rapidly adopted by rice growers throughout the southern rice growing states. In 2005, over 240000 ha were planted to Clearfield rice, which is about 17% U.S. rice acreage (Anonymous, 2006).
The market value of rough rice is based, to a large extent, on its milling quality or milling yield (Calderwood et al., 1980). Milling yield includes milled whole grain or head rice and total milled rice (milled whole and broken grains combined). The percentage of rice grains that remain three-fourths their normal length or more after the hulls and bran layer are removed during milling is referred to as head rice yield (Gravois and Helms, 1998).
There is only limited research on rice planting date effect, and most of the research is on transplanted rice (Ghosh et al., 2004). The very limited research that was conducted in the USA involved either traditional tall cultivars or modern cultivars under drill-seeded conditions. In Louisiana, Jodon and McIlrath (1971) studied the planting date effects by using rice cultivars and breeding lines of both long- and medium-grain types seeded at late March, late April, mid May, and mid June. Planting date effects on maturity, plant height, and yield were observed for both long- and medium-grain genotypes. In most tests, April plantings had the highest average grain yields; however, June plantings had the lowest average grain yields. Rice planted at mid-May was taller and had a shorter growing duration than that of late March plantings. Planting date x cultivar interaction for grain yield was also observed.
In Arkansas, Adair (1940), who studied the effect of planting date on grain yield and milling quality, concluded that late April through May was the optimum time for planting rice to achieve both high grain rice and head rice yields. Most of the early and midseason cultivars produced rice of higher milling yield when they matured in late September or early October than when they matured before 15 September. A recent study by Gravois and Helms (1998) with modern cultivars indicated that rice planted in March had low seedling stands, while delayed planting in June resulted in shorter maturity, lower grain yield, but higher head rice yield. Rice cultivars with poor milling had lower and more variable head rice yield when seeded earlier. By analyzing both Arkansas and Louisiana yield data from the studies conducted in 1990s with modern cultivars and from 1960s and 1970s with older cultivars, Slaton et al. (2003) revealed that modern cultivars produced maximum grain yields when planted from 16 February through 28 March at Crowley, LA; and 29 March through 26 April at Stuttgart, AR. Older cultivars grown in 1960s and 1970s had slightly later optimum planting dates.
Even though rice is mainly drill seeded in Arkansas, Missouri, and Mississippi, considerable U.S. rice acreage is water seeded, especially that near the Gulf coast and in California (Street and Bollich, 2003). Water seeding allows rice to be planted on time under extreme wet weather conditions, as well as offers red rice control for non-herbicide-tolerant conventional rice cultivars (Smith, 1981). All previous rice planting date studies were performed on non-herbicide-tolerant conventional cultivars and under drill-seeded conditions. Rice cultivars, especially those with low seedling vigor, may perform differently under water-seeded conditions that normally associate with low O2 levels and constant flooding. Therefore, the objectives of this study were to investigate the planting date effects on grain yield, milling quality, and other agronomic traits of both Clearfield rice (cultivar and hybrid) and conventional rice cultivars under water-seeded conditions.
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MATERIALS AND METHODS
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Field experiments were conducted at the Louisiana State University AgCenter's Rice Research Station at Crowley, LA (LSU RRS), from 2003 to 2005. The soil was a Crowley silt loam (fine, smectitic, hyperthermic Typic Albaqualfs). Each year, between 12 and 15 rice cultivars, hybrids, and breeding lines were planted every 2 wk from late February to late June or early July. Because most rice genotypes, especially breeding lines, varied from year to year, only four commonly grown cultivars or hybrids (Clearfield cultivar CL161, Clearfield hybrid CLXL8, and conventional cultivars Cheniere and Cocodrie) tested in 3 yr were included for the analysis. CL161, released by BASF and LSU RRS in 2002, accounts for the majority of current Clearfield rice acreage, while CLXL8, developed by RiceTec, Inc. (Alvin, TX) in 2003, was the first Clearfield hybrid to be commercialized in the USA. On the other hand, both Cheniere (Linscombe et al., 2006) and Cocodrie (Linscombe et al., 2000) are the predominant conventional long-grain cultivars in the southern USA, especially in Louisiana, Mississippi, and Texas. In 2005, the rice area planted to CL161, Cheniere, and Cocodrie was about 606000 ha, which represented 52.7% of southern U.S. rice acreage (Anonymous, 2006). The detailed genotype information can be found in the following research reports: Linscombe et al. (2003), Linscombe et al. (2004), and Linscombe et al. (2005). A split-plot design was used with planting date as main plot and cultivar as subplot. Main plots were not replicated; however, subplots (cultivars) within each main plot were completely randomized with three replications. The eight planting dates were late February (D1), mid March (D2), early and mid April (D3 and D4), early and mid May (D5 and D6), late May or early June (D7), and mid June or early July (D8). Exact planting dates were listed in Table 1. Seeding rates were 168 kg ha–1 for pure line cultivars and 56 kg ha–1 for hybrids as recommended (Saichuk et al., 2006). Before planting, rice seeds were immersed in the water for 24 h before being drained, then kept moist for another 24 h to sprout. The presprouted seeds were evenly distributed by hand into each plot measuring 1.4 x 4.9 m. At the 3- to 4-leaf stage, the plots were briefly drained for application of fertilizer and herbicides. The rice was fertilized with 164 kg N ha–1 by broadcasting on the dry soil surface. The Clearfield cultivar/hybrid was not treated with imazethapyr herbicide. Instead, they were treated like all conventional cultivars with a common herbicide program that included tank mix of 3.36 kg ha–1 propanil, 3.36 kg ha–1 molinate, and 0.04 kg ha–1 halosulfuron or 0.04 kg ha–1 bensulfuron methyl before the permanent flood. To evaluate the response of these rice genotypes to various pathogens and abiotic stresses, neither fungicides nor plant growth regulators were applied in this study.
The daily maximum and minimum air temperatures and precipitation data were recorded by the weather station at LSU RRS. Because it is very time-consuming to count the seedling stand on broadcasted plots compared with drill-seeded plots, actual stand for each plot (average of two 4-ft2 subsamples) was only counted on four out of eight total planting dates in 2005. Instead, visual emergence, a simple and more practical seedling stand measurement, was visually rated 10 to 14 d after emergence (1- to 2-leaf stage) on a 1-to-9 scale, where 1 = excellent, and 9 = no stand for all planting dates in 2003 and 2005. Pearson's correlation analysis was performed to estimate the correlation coefficient between actual stand counts and visual emergence ratings. For each plot, maturity was recorded as number of days from emergence to 50% heading; and plant height was taken at maturity by averaging the lengths from the soil surface to the tip of the three tallest panicles. Milling samples (0.5 m2 each) were individually hand-harvested at about 180 g kg–1 moisture content from the first two blocks at each planting date. The samples were threshed and dried to 120 g kg–1 moisture content then stored in a cold room that was kept at 20°C for 2 mo before milling. Total milled rice and head rice recovery were estimated from 125 g of cleaned rough rice samples following the procedure described by Adair et al. (1972). After milling samples were taken, all remaining rice plants in each plot were harvested with an Almaco plot combine (Almaco, Nevada, IA), and grain yield was adjusted to 120 g kg–1 moisture content.
Because of the severe blackbird damage, the February planting dates were excluded from analysis. The visual emergence ratings were transformed by the square root of the actual ratings before statistical analysis. This transformation is necessary to minimize the problem associated with small data (<10), when the variance tends to be proportional to the mean (Gomez and Gomez, 1984). The General Linear Model procedure of SAS version 9.0 was used in the data analysis (SAS Institute, Cary, NC). Planting dates were assigned to main plots and Cultivars to subplots. Since main plots (Planting dates) were not repeated in each individual year, Years were treated as replications as that reported by Chen et al. (2003). Planting date means across all cultivars, as well as Cultivar means at a given planting date, were separated by the least square difference (LSD) test at the 0.05 probability level based on the procedures described by Gomez and Gomez (1984).
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RESULTS
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Planting date effects were significant for grain yield, days to 50% heading, plant height, and head rice yield (Table 2). The Cultivars effects were significant for all traits measured except for total milled rice yield. Planting date x Cultivar interaction was not significant for all traits.
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Table 2. Mean squares of grain yield, visual emergence, head rice and total milled rice, days to 50% heading, and plant height of four selected Clearfield and conventional rice cultivars, Crowley, LA, 2003–2005.
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Rice seeded at two April planting dates (D3 and D4) produced the highest grain yield with the means of 7.94 and 7.94 Mg ha–1, respectively (Fig. 1). The mean grain yields of two May planting dates (D5 and D6) were 6.76 and 6.28 Mg ha–1, respectively, which were lower (P < 0.05) than that of two April planting dates. Further grain yield reduction was observed for rice planted in June and July (D7 and D8), with the means of 4.51 and 3.64 Mg ha–1, respectively. Rice seeded at mid March also yielded lower (P < 0.05) than those seeded in April but similar to those seeded in May.
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Fig. 1. Grain yields, visual emergence, days to 50% heading, plant heights, head rice, and total milled rice means of seven planting dates averaged over years and cultivars. Bars with the same letters above are not significantly different based on Fisher's protected LSD. Significance level of P = 0.10 was used for separation of visual emergence and total milled rice means, while P = 0.05 was used for all other traits. Visual emergence is a visual rating of seedling stand at 1- to 2-leaf stage, where 1 = excellent stand and 9 = no stand.
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When averaged over different planting dates and years, Clearfield hybrid CLXL8 had the highest mean grain yield of 7.21 Mg ha–1 among all four rice genotypes followed by 6.00, 5.93, and 5.53 Mg ha–1 for CL161, Cocodrie, and Cheniere, respectively. CLXL8 also had the highest mean grain yields in all planting dates except for the July planting (Fig. 2). Compared with conventional cultivars, Clearfield cultivar CL161 had similar grain yield as Cocodrie but was higher than Cheniere. The yield fluctuation pattern of Clearfield rice across all planting dates was similar to that of conventional rice.
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Fig. 2. Mean grain yields, visual emergence, days to 50% heading, plant heights, head rice, and total milled rice yields of Clearfield rice cultivar CL161, Clearfield hybrid CLXL8, and conventional rice cultivars Cheniere and Cocodrie at seven planting dates, Crowley, LA, 2003–2005. Bars with the same letters above are not significantly different based on Fisher's protected LSD (P = 0.05). Visual emergence is a visual rating of seedling stand at 1- to 2-leaf stage, where 1 = excellent stand and 9 = no stand.
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Planting date affects head rice yields (Fig. 1). When averaged over cultivars and years, D4 produced the highest mean head rice yield among the seven planting dates of 652 g kg–1 followed by D6 of 637 g kg–1. Interestingly, the lowest head rice mean of 597 g kg–1 appeared at D7 that was planted right after D6, while the second lowest mean head rice yield of 606 g kg–1 observed at D5 that was right after D4 that had the highest head rice. Nevertheless, head rice yield improved at D8, which had a mean of 635 g kg–1. When averaged over planting dates and years, Clearfield cultivar CL161 had the highest mean head rice yield of 644 g kg–1 followed by conventional cultivars Cheniere (642 g kg–1) and Cocodrie (636 g kg–1). However, the Clearfield hybrid CLXL8 had the lowest and most variable head rice yield of 584 g kg–1. CLXL8 had the lowest head rice yield in all seven planting dates, while CL161 had the highest head rice yield in D2, D3, D6, and D8 with the conventional cultivars leading on the other three occasions (Fig. 2).
Compared with head rice, total milled rice yield was less affected by planting date and was less variable among the four tested genotypes (Fig. 1 and 2). Total milled rice yield had the similar fluctuation pattern to head rice yield over planting dates. Among the seven planting dates, D4 had the highest total milled rice of 717 g kg–1; while D5 produced the lowest total milled rice yield of 688 g kg–1. The mean total milled rice yields of four genotypes were neither significantly different across planting dates and years nor at different planting dates.
Visual emergence ratings correlated with actual stand counts (r2 = 0.83) for rice water seeded at D2, D4, D6, and D8 planting dates in 2005 (stand count data not shown). The average visual emergence of four rice genotypes was different (P = 0.0611) at seven planting dates (Fig. 1). Rice planted at the two early planting dates (D2 and D3) had better seedling stand than the later ones. However, rice planted at early May (D5) had the worst seedling stand with a visual emergence rating of 6.3 followed by 5.6 for both D4 and D8. The dramatic temperature drops caused by cold fronts in early May of 2004 and 2005 (Fig. 3) may contribute to the lowest seedling stand observed at D5. Clearfield CL161 and CLXL8 had better seedling stand than two conventional cultivars (Fig. 2).
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Fig. 3. Ten-day average maximum (T max) and minimum (T min) air temperatures and 10-d accumulative rainfall from 1 March to 20 October recorded at Rice Research Station, Louisiana State University AgCenter, Crowley, LA, 2003 to 2005.
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The maturity of both Clearfield and conventional rice as measured by number of days from emergence to 50% heading was affected (P = 0.0357) by planting date (Fig. 1). It took about 90 d for the rice planted at or before 2 May (D2–D5) to reach 50% heading. However, the number of days was reduced to 81 and 82 for rice seeded at mid May (D6) and early June (D7) and further reduced to 72 d after early June (D8). CL161 had a later maturity with a mean of 87 d across planting dates and years, while the other three genotypes had a similar maturity of 84 d. However, there was no significant difference on accumulative degree-days (>10°C) from emergence to 50% heading among different planting dates (data not shown).
Planting date also had a significant effect on rice plant height (Fig. 1 and 2). Rice seeded early (D2) and late (D7–D8) during the growing season was significantly (P = 0.0018) shorter than those seeded in April and May (D3–D6). The average plant height of mid-April plantings (D4) was the highest at 98.4 cm followed by 95.2 cm of early May plantings (D5). However, rice planted at early June (D7) had the shortest plants with a mean of 83.2 cm followed by 85.5 cm of D8. Clearfield hybrid CLXL8 was significantly taller than both Clearfield and conventional cultivars.
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DISCUSSION
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Both Clearfield rice (cultivar and hybrid) and non-herbicide-tolerant conventional rice produced the highest grain yield when water seeded the first half of April. Significant grain yield reduction was observed for rice planted in May, while substantial reduction occurred thereafter. Rice seeded at mid March had similar grain yield to those seeded in May but significantly lower than rice planted in April. Similar results on older cultivars were reported in Louisiana by Jodon (1967). Rice seeded at 25 April had the highest mean yield followed by that seeded at 7 April and 11 May, while the 16 June planting had the lowest grain yield for both long- and medium-grain types. Research indicated that the optimum seeding date tended to be earlier for modern cultivars planted in the 1990s than the old cultivars planted in the 1960s at Crowley, LA (Slaton et al., 2003). The earlier optimum planting date may be attributed to the breeding achievements for not only improving yield potential but also reducing growth duration. Even though the optimum planting date varies with region, a similar trend of yield fluctuations was reported in other states. In subtropical southern Florida, Jones and Snyder (1987) demonstrated that rice drill seeded in March yielded higher than plantings in April and May for both traditional tall and modern semidwarf cultivars. In Arkansas, Gravois and Helms (1998) found that rice drill seeded in late April and early May yielded higher than that planted at both earlier and later planting dates.
Several physiological and biological factors may be responsible for the lower grain yield for the rice planted after mid May in this experiment. In Florida, Jones and Snyder (1987) found that late planted rice had less filled grains panicle–1 than early planted rice, which was in coincidence with the lower daily solar radiation and climatic productivity index (from 25 to 0 d before flowering) associated with late planted rice. In Arkansas, Faw and Johnston (1975) reported that the low grain yield of late planted rice was caused by shortened growth period, lower panicle density, and low biomass accumulation at heading. The heavier rice water weevil (Lissorhoptrus oryzophilus Kuschel) infestation observed in late planted rice also contributed to the lower grain yield. Zou et al. (2004) showed that feeding by L. oryzophilus larvae resulted in extensive damage to root system, which, in turn, caused the reduction of tiller number, shoot biomass, and even established stand.
Both Clearfield cultivar CL161 and Clearfield hybrid CLXL8 had similar responses to planting date as compared with conventional cultivars. Bollich et al. (2002) reported that Clearfield rice, especially the first generation cultivars CL121 and CL141, yield lower than leading conventional cultivars, such as Cocodrie. However, the mean grain yield of CL161 in this study was similar to that of Cocodrie but higher than the conventional cultivar Cheniere. The diminishing yield gap between Clearfield and conventional cultivars may have resulted from the intensive breeding effort to incorporate the herbicide resistance into the newer cultivars or breeding lines. In fact, CL161 was developed from a mutant derived from the commercial cultivar Cypress, which had good yield potential and excellent milling quality. On the other hand, heterosis accounts for the outstanding yield advantage of Clearfield hybrid CLXL8 (Virmani, 2003; Walton, 2003).
Rice planted at mid April also produced the highest head rice yield followed by those planted at mid May. Surprisingly, rice water seeded immediately after those two dates had the lowest head rice yields. The unexpected low head rice at early May plantings was probably related to the low seedling stand (Fig. 1). Gravois and Helms (1996) suggested that lower plant stands will produce more secondary and tertiary tillers than normal established stands. Excessive tillering extends the grain filling period of rice, which can cause the mixtures of fully filled mature and partially filled immature rice kernels at harvest. Immature kernels break easily during milling, thus lower the milling yield. However, the low head rice of early June plantings seems related to the hot, sunny, and dry days followed by humid or dewy nights of late August and early September (Fig. 3), when the rice is approaching maturity. Meanwhile, the declining temperature and increased precipitation after late September might contribute to the improved head rice yield for the late June or early July plantings that matured in early October (Fig. 1). Jodon and McIlrath (1971) suggested that rice maturing during extremely hot weather will produce considerable sun-checking (cracking of the rice grain) that will lower the head rice yield. Clearfield cultivar CL161 had the highest head rice yield, while Clearfield hybrid CLXL8 had lowest head rice yield among all four genotypes, which was especially significant for rice planted at mid March and after June 1. Total milled rice yield was similar among the four genotypes, and less affected by planting date.
Visual emergence, which is a measure of the plant stand establishment after emergence, was also affected by planting date for both Clearfield and conventional rice. However, our results were different from those conducted under drill-seeded conditions (Jones and Snyder, 1987; Gravois and Helms, 1998). Rice seeded at mid March and 1 April had better seedling stand than those seeded later. Gravois and Helms (1998) reported that the established plant stands were low only for rice drill seeded at mid March, but satisfactory for the later plantings. The possible explanation of the difference is that the water-seeded rice is more susceptible to the water weevil (Lissorhoptrus oryzophilus Kuschel) damage than is drill-seeded rice (Rice et al., 1999). Thompson et al. (1994) indicated that the rice planted before mid April was more tolerant to the water weevil infestation than later-planted rice. In this study, the heavier water weevil infestation was observed for rice planted after 2 May (data not shown).
The time between seedling emergence and 50% heading was longer for both Clearfield and conventional rice when water seeded before 2 May but declined for the later plantings. The extended maturity for the early seeded rice, as well as the significantly shortened maturity for the late planted rice was related to the accumulation speed of the degree-day units that remains relative constant for a given rice cultivar (Slaton et al., 2003). Clearfield cultivar CL161 matured significantly later than the other genotypes.
Rice plant height was affected by both planting date and genotype. Rice seeded at mid April was the tallest, followed by those seeded at early April and two May planting dates. However, rice planted at mid March and after 1 June was significantly shorter than those seeded at the other dates. The stress on vegetative growth was apparently caused by the cold air and soil temperatures in the early period of rice growing season, as well as the hot and drier weather late in the season. Clearfield hybrid CLXL8 was significantly taller than both Clearfield and conventional cultivars. Lodging susceptibility is one of the shortcomings of hybrid rice, which limits its wide adoption in rice growing area near the Gulf coast (Walton, 2003).
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CONCLUSIONS
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Clearfield rice had similar reactions as conventional rice to planting date. Both Clearfield rice (cultivar and hybrid) and non-Clearfield rice had the highest grain yield when water-seeded from the beginning of April to mid April. Significant grain yield reduction was observed for rice planted in May, while substantial reduction happened thereafter. Rice seeded at mid March had similar grain yield to that seeded in May but significantly lower than rice planted in April. In contrast to drill-seeded conditions, rice water-seeded at mid March and 1 April had better seedling stand than those seeded later. Both Clearfield and conventional rice that was water-seeded before 2 May had a longer growing season than those seeded later. Meanwhile, rice planted at mid March and after 1 June was significantly shorter than those seeded from early April to early May. Rice planted at mid April also produced the highest head rice yield, followed by those planted at mid May. Surprisingly, rice seeded immediately after those two dates had the lowest head rice yield. These low head rice yields were probably related to the poor stand establishment and/or hot and dry weather during late August and early September when the rice headed. The Clearfield cultivar CL161 had higher head rice yield than conventional cultivars. However, the Clearfield hybrid CLXL8 had poor head rice yield, which was especially significant when planted at mid March or delay planted after 1 June.
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NOTES
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Approved for submission by the Director of the Louisiana Agric. Exp. Stn. as Manuscript no. 06-61-0660.
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ABSTRACT
INTRODUCTION
