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Published in Agron J 100:381-386 (2008)
DOI: 10.2134/agrojnl2007.0047
© 2008 American Society of Agronomy
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RICE

Hybrid Rice Response to Nitrogen Fertilization for Midsouthern United States Rice Production

Timothy W. Walkera,*, Jason A. Bonda, Brian V. Ottisb, Patrick D. Gerardc and Dustin L. Harrelld

a Delta Research and Extension Center, Mississippi State Univ, P.O. Box 197 Stoneville, MS 38776
b RiceTec, Inc., 822 Woodruff, Sikeston, MO 63801
c Dep. of Applied Economics and Statistics, Clemson Univ., 291 Barre Hall, Clemson, SC 29634-0313
d LSU AgCenter–Rice Research Station, 1373 Caffey Rd., Rayne, LA 70578. Contribution of the Mississippi Agric. and For. Exp. Stn. Publication J-11164. This research was funded in part by the Mississippi Rice Promotion Board and the Louisiana Rice Research Board

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


   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Limited data representing the southern U.S. production area exists for N nutrition in hybrid rice (Oryza sativa L.) cultivars. Experiments were conducted to evaluate the effects of N fertilizer rates and application timings on grain and whole milled rice yield for ‘XL723’ (RiceTec, Inc., Alvin, TX) as compared with widely grown inbred rice cv. Cocodrie on clay soils and Cheniere on silt loam soils. A factorial arrangement of cultivar, preflood (PF), panicle differentiation (PD), and panicle emergence (PE) N rates were established in Louisiana, Mississippi, and Missouri for a total of three site-years each for clay and silt loam soils. On clay soils, XL723 grain yield increased with increasing PF-N rate reaching 12,332 kg ha–1 at a PF-N rate of 202 kg N ha–1. ‘Cocodrie’ grain yield did not substantially increase with PF-N >151 kg N ha–1. Averaged across cultivars, a PD-N rate of 50 kg N ha–1 increased grain yields by 729 kg ha–1 when 101 kg N ha–1 was applied; however, as PF-N rate increased, the effects of PD-N were not significant. On silt loam soils, grain yields were 327 kg ha–1greater when 151 kg N ha–1 was applied PF compared with 101 kg N ha–1. Furthermore, a PE-N rate of 50 kg N ha–1 increased grain yield by 333 kg ha–1. On clay soils, maximum whole milled rice was obtained when a minimum of 151 kg N ha–1 was applied PF and 50 kg N ha–1 was applied at PE. On silt loam soils, the 101 kg N ha–1 PF rate produced 625 mg g–1 whole milled rice for Cheniere, whereas, the greatest concentration (613 mg g–1) of whole milled rice for XL723 was produced with 202 kg N ha–1. Finally, yield potential was 17 to 20% greater for XL723 compared with the inbred cultivars; however, at equal N rates, whole milled rice was higher with conventional inbred cultivars compared with XL723. Hybrid rice can be used in the southern U.S. rice-growing region to increase rice yield per unit of land area. Preflood N rates on hybrid rice should be equal to or greater than inbred cultivars. For practical implications, N management for hybrid rice should include a PE application to increase yield, whole milled rice, and also decrease the potential for lodging. As straw-strength increases with new rice hybrids, PF-N management should be reevaluated for increased yield potential.

Abbreviations: PD, panicle differentiation • PE, panicle emergence • PF, preflood


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher.

Received for publication February 1, 2007.
   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Over the last half-century, rice has been the source for approximately 18 to 20% of the world's human caloric consumption (Anonymous, 2007a). More specifically, it is considered the main food staple for more than 50% of the world's population (Childs, 2004). When considering the amount of grain used for food, rice produces more food energy per hectare than any other cereal (Eggum, 1979; FAO, 2001; Childs, 2004). The United States only accounts for approximately 1.5% of world rice production; however, it accounts for 14% of the total world exports and is ranked fourth behind Thailand, Vietnam, and India, in 2005 (Childs, 2005). The United States exports more than 40% of its production annually (Childs, 2005). Since 2002, world rice stocks have decreased dramatically while population has increased (Fig. 1 ). Because of the importance of rice for supplying food, there is a demand for higher grain yield per hectare. It has been suggested that by 2025, global rice production must increase by more than 50% from mid-1990 levels to meet that demand (Peng and Yang, 2003). Because of natural resource restraints, much of this increase must come from increased yields (Smith et al., 2007).


Figure 1
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  		Fig. 1. World population growth and world rice stocks to use ratio from 1990 to 2005 (Childs, 2004; Anonymous, 2007b)

 
China began addressing increased production per unit of area in the 1970s with commercialization of hybrid rice developed by Yuan Long Ping (Li and Yuan, 2000). Hybrid rice uses heterosis so that root mass and yield components such as biomass, tillering, panicle length, and spikelet number per panicle are superior to the respective parent lines. Since its inception, hybrid rice typically produces 15 to 25% greater yield when compared with inbred cultivars. Because of the yield advantage gained with hybrids, more than 50% of the current rice production area in China is planted to hybrid rice, and other Asian countries are following China's lead (Li and Yuan, 2000). Hybrid rice in the United States was commercialized by RiceTec, Inc., headquartered in Alvin, TX, in 2000. Based on hectarage by cultivar surveys conducted by the southern U.S. rice-growing states, approximately 100,000 ha of hybrid rice was produced in 2006 (S. D. Linscombe, personal communication, 2007; Texas A&M, 2007; N. W. Buehring, personal communication, 2007; B. Beck, personal communication, 2007; C. E. Wilson, personal communication, 2007). This area represented approximately 10% of the hectarage planted to rice in the midsouthern United States in 2006.

Nitrogen nutrition has been thoroughly researched for inbred cultivars in the United States and is well documented by Norman et al. (2003); however, a review of the literature revealed that very little public information exists (Ottis and Talbert, 2005) for rice hybrids produced in the highly mechanized, high-input, southern U.S. rice production system. The objectives of this research were to evaluate the effects of N rate and time of application on grain yield and whole milled rice of the XL723 hybrid (RiceTec, Inc., Alvin, TX) and compare it with standard southern U.S. inbred cv. Cocodrie (Linscombe et al., 2000) and Cheniere (Linscombe et al., 2006).


   MATERIALS AND METHODS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
An experiment was conducted in 2005 and 2006 in Louisiana, Mississippi, and Missouri to evaluate the response of XL723 to N application rates and timings. The experiment was conducted on Sharkey clay soil (very-fine, smectitic, thermic Chromic Epiaquerts) in Mississippi in 2005 and 2006, and in 2006 in Missouri (Table 1 ). Additionally, the experiment was conducted on Forestdale silt loam (fine, smectitic, thermic Typic Endoaqualfs) in Mississippi in 2005 and 2006 and on Crowley silt loam (fine, smectitic, thermic Typic Albaqualfs) in 2006 in Louisiana. Thus, results were drawn from a total of six site-years.


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  		Table 1. Site description for experiment locations including soil series, soil description, soil pH, and organic matter (OM), dates of emergence and N application for preflood (PF), panicle differentiation (PD), and panicle emergence (PE).

 
Treatments were arranged as a factorial of cultivar, PF-N rate, PD-N rate, and PE-N rate in a randomized complete block design with four replications. Preflood N was applied to dry soil when rice reached the five-leaf stage. The PD growth stage was reached when the length between the two uppermost nodes reached approximately 1 cm. Panicle emergence growth stage was reached when approximately 5% of the panicles were emerged from the sheath. Levels of PF-N were 101, 151, and 202 kg N ha–1; whereas levels of PD- and PE-N were 0 and 50 kg N ha–1. All N treatments were applied as urea (46% N). Zero N plots were included for all site-years and for all cultivars so that response curves could be derived (Fig. 2 and 3 ), which indicate the relative N-supplying capacity of the two soil textures. XL723 was the hybrid cultivar for both clay and silt loam soils; however, Cocodrie was chosen as the comparison inbred cultivar for clay soils and Cheniere was chosen for silt loam soils. This decision was made primarily on the basis of popularity by soil type in 2005 and 2006 for the southern U.S. rice growing region.


Figure 2
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  		Fig. 2. Mean grain yield response to preflood N rate for ‘XL723’ and ‘Cocodrie’ on clay soil. XL723 yield = -0.15x2 + 66.23x +4987. Cocodrie yield = -0.13x2 +52.67x + 4597.

 

Figure 3
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  		Fig. 3. Mean grain yield response to preflood N rate for ‘XL723’ and ‘Cheniere’ on silt loam soil. XL723 yield = -.08x2 + 33.09x +8355. Cheniere yield = -0.07x2 +27.22x + 6972.

 
Plots measuring approximately 8.5 m2 were drill-seeded from late March to early May (Table 1), which corresponds to optimum planting period from southern Louisiana to southern Missouri. Seeds for each plot were individually weighed so that a target of 34 and 95 kg seed ha–1 could be drill-seeded for XL723 and the inbred cultivars, respectively. Rice was grown in an upland condition until it reached the five-leaf growth stage. At this point a flood was established. When rice reached the PD and PE growth stages, N was broadcasted by hand onto each plot. Pest control measures were conducted according to state recommendations (Miller and Street, 2000; Linscombe et al., 1999) as needed to ensure an environment conducive for optimum production and to alleviate variability due to weeds, diseases, or insects.

When rice grain reached 170 to 200 mg g–1 moisture, plots were harvested with a small plot combine. Plot yields were adjusted to a standard of 120 g kg–1 moisture content. Subsamples were collected from each plot so that whole milled rice could be determined (Adair et al., 1972).

Rice grain yield and whole milled rice data were subjected to the Mixed Procedure (Littell et al., 1996; SAS, 2003). Cultivar, PF-N, PD-N, and PE-N were fixed effects, whereas site-year, replications nested within site-year, and all possible interactions containing these effects were considered random effects. Because two soil textures were present, separate analyses were conducted for clay soils and silt loam soils. Considering site-year a random affect allowed inferences to be made over a range of environments. This statistical approach has been used successfully in previous research findings (Carmer et al., 1989; Ottis et al., 2004; Bond et al., 2005; Walker et al., 2006). Type III statistics were used to test fixed effects and interactions among fixed and least square means at the P < 0.05 was used for mean separation.


   RESULTS AND DISCUSSION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Grain Yield
Rice grain yield on clay soils was affected by an interaction among cultivar and PF-N rate (P = 0.0111), as well as the PF-N rate by PD-N rate interaction (P = 0.0251) (Table 2 ). Mean grain yield pooled across PD- and PE-N increased with increasing PF-N rate for XL723, whereas mean grain yield for Cocodrie did not significantly increase when PF-N exceeded 151 kg N ha–1 (Table 3 ). Mean grain yield pooled across cultivar and PE-N for clay soils was significantly increased when 50 kg N ha–1 was applied at PD following a 101 kg N ha–1 application at PF; however, at the two highest PF-N rates, PD-N applications did not increase grain yield (Table 4 ).


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  		Table 2. Significance of the main effects [cultivar (CV), preflood N (PF), panicle differentiation N (PD), and panicle emergence N (PE)] and interactions among the main effects for rice grain yield and whole milled rice pooled across environments for clay and silt loam soils.

 

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  		Table 3. Rice grain yield as affected by an interaction among cultivar and preflood N rate pooled across panicle differentiation and panicle emergence N rate on clay soils.

 

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  		Table 4. Rice grain yield as affected by an interaction among preflood N rate and panicle differentiation N rate pooled across cultivar and panicle emergence N rate on clay soils.

 
Grain yield response to N treatments was also observed on silt loam soils. Cultivar, PF-N, and PE-N individually influenced grain yield (Table 2). Pooled across cultivar, PD-N, and PE-N, grain yield with 151 and 202 kg N ha–1 applied PF was greater than when 101 kg N ha–1 was applied PF (Table 5 ). Additionally, when means were pooled across cultivar, PF- and PD-N, grain yield was greater when 50 kg N ha–1 was applied at PE compared with no N applied at PE.


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  		Table 5. Rice grain yield as affected by preflood N and panicle emergence N on silt loam soils.

 
The higher grain yields at the N rates applied for the hybrid cultivar compared with the inbred cultivar on the clay soils suggest the hybrid used the applied fertilizer N more efficiently (kg N per kg grain) and/or the hybrid absorbed more native soil N. An exact explanation for the greater N efficiency of hybrid rice extends beyond the scope of the current research and is further complicated by PF-N response curves for the hybrid and inbred cultivars on clay and silt loam soils (Fig. 2 and 3). Figure 2 demonstrated that as PF-N rate increased on clay soils, the relative yield response by the hybrid increased when compared with the inbred cultivar. However, the response curves were very similar on silt loam soils except that the hybrid produced greater yields at all N rates. It has been hypothesized that greater root mass and number facilitates greater N absorption by hybrids (Yang et al., 1999). Where PF-N response was different on clay soils compared with silt loam soils, this hypothesis is valid because NH4+ diffusion for clay soils has been determined to be as much as 12 times less per day compared to sandy soils (Trostle et al., 1998). Greater root density in the rhizosphere would theoretically be more competitive for absorption of NH4+ (Bhadraray et al., 2002), and thus may offset differences in NH4+ diffusion.

The interaction among PF-N and PD-N on clay soils demonstrates the importance of N uptake during the vegetative growth stage for both hybrid and inbred cultivars. When an insufficient amount of N was applied PF (101 kg N ha–1), a 7% yield response was obtained when PD-N was applied (Table 4). However, even when PD-N was applied following PF-N at 101 kg N ha–1, yields were still 443 kg ha–1 less than when 151 kg N ha–1 was applied PF with no PD-N. Because these values are pooled across PE-N, actual differences could potentially be greater. Similar results have been reported for semi-dwarf cultivars produced in the southern United States (Bollich et al., 1994; Bufogle et al., 1997; Wilson et al., 1998; Norman et al., 2000a; Walker, 2006); however, split applications (basal, tillering, PD, and flowering) for hybrids have been more productive in Asia (Surekha et al., 1999; Wopereis-Pura et al., 2002; Balasubramanian, 2002).

Grain yield response to PF-N for XL723 and Cheniere was similar on silt loam soils (Fig. 3) where yields were maximized following PF-N at 151 kg N ha–1. Silt loam soils do not have as high affinity for NH4+ compared with clay soils, and therefore did not require as much PF-N to optimize vegetative N uptake (Chen et al., 1989). However, rice grain yields were increased by PE-N on silt loam soils. Hybrid rice response to reproductive N has been attributed to the fact that as much as 20% of the total accumulated N is absorbed after heading (Yang et al., 1999). Furthermore, an addition of N during the late-reproductive growth stages helps alleviate negative effects of catabolism, that is, translocation of N from leaves and stems to panicles, allowing plants to maintain higher photosynthetic rates (Chen et al., 2006) in green tissues, which increases grain filling (Nie et al., 2005).

Whole Milled Rice
Preflood N (P = 0.0004) and PE-N (P ≤ 0.0001) influenced whole milled rice on clay soils (Table 2). A minimum of 151 kg N ha–1 applied PF was needed to achieve the greatest amount of whole milled rice (Table 6 ). Additionally, when 50 kg N ha–1 was applied at PE, whole milled rice was increased. An interaction among cultivar and PF-N affected whole milled rice on silt loam soils (P ≤ 0.0001) (Table 2). Whole milled rice increased with increasing PF-N rate for XL723; however, whole milled rice was independent of PF-N rates for Cheniere (Table 7 ). An interaction among cultivar and PD-N also affected whole milled rice on silt loam soils (P = 0.0152) (Table 2). Though 50 kg N ha–1 applied at PD produced greater whole milled rice than 0 kg N ha–1, the difference was negligible (<1%). The greatest difference occurred between cultivars where Cheniere produced 15 to 27 mg whole grain per gram of milled rice greater than XL723 across all N treatments (Table 8 ). Pooled across cultivar and PF-N rate, whole milled rice was affected by an interaction among PD-N and PE-N on silt loam soils (P = 0.0255; Table 2). When no fertilizer N was applied at PD, an application of N at PE did not affect whole milled rice (Table 9 ). However, when 50 kg N ha–1 was applied at PD, an additional 50 kg N ha–1 increased whole milled rice. The difference was only 10 mg kg–1 (1%) and based on current premiums for whole milled rice and N prices, this difference has no practical implications.


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  		Table 6. Whole milled rice as affected by preflood N and panicle emergence N on clay soils.

 

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  		Table 7. Whole milled rice as affected by an interaction among cultivar and preflood N rate pooled across panicle differentiation and panicle emergence N rate on silt loam soils.{dagger}

 

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  		Table 8. Whole milled rice as affected by an interaction among cultivar and panicle differentiation N pooled across preflood and panicle emergence N rate on silt loam soils.{dagger}

 

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  		Table 9. Whole milled rice as affected by an interaction among panicle differentiation N and panicle emergence N pooled across cultivar and preflood N on silt loam soils.{dagger}

 
Variable whole milled rice responses to N fertilizer applications during the late reproductive stage (PE) have been observed for U.S. long grain cultivars (Walker et al., 2006; Norman et al., 2000b; Bond and Bollich, 2007; Jongkaewwattana et al., 1993). Whole milled rice of ‘Wells’ (Moldenhauer, 2001) and Cocodrie was 3 and 1% greater, respectively, when 50 kg N ha–1 was applied at PE compared with PD (Walker et al., 2006). Norman et al. (2000b) reported that ‘Lagrue’ (Moldenhauer et al., 1994) and ‘Cypress’ (Linscombe et al., 1993) whole milled rice was greater when 45 kg N ha–1 was applied at PE in one of 2 yr. Bond and Bollich (2007) evaluated Cocodrie, Cheniere, ‘Cypress’, ‘Francis’ (Moldenhauer et al., 2007), and Wells on Crowley silt loam and Sharkey clay soils and found that an N application at PE did not increase whole milled rice, but rather the PF-N rate that produced maximum grain yield also produced maximum whole milled rice. Similar results were reported for short, medium, and long grain varieties produced in California (Jongkaewwattana et al., 1993). Flowering applications of N (30–40 kg N ha–1) increased whole milled rice by 10% points at IRRI (Perez et al., 1996). Similar results were reported by Leesawatwong et al. (2005), where increased whole milled rice was positively correlated with the relative abundance of storage proteins in the lateral region of the endosperm.


   CONCLUSIONS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
Hybrid rice production has increased worldwide since its introduction in 1976. Because of the importance of the U.S. rice supply with respect to export markets, yield gains will be necessary to meet future world demand. Data reported here indicate that hybrid rice has a 17 to 20% yield advantage over popular southern U.S. inbred cultivars at equal N rates; however, whole milled rice was typically greater with inbred cultivars. Traditional PF-N strategies for southern U.S., semi-dwarf inbred cultivars were suitable for the hybrid XL723; however, the data suggests there is potential to further increase grain yield with hybrids with higher PF-N rates. Currently, because of the propensity for hybrid rice to lodge, PF-N rates seldom exceed 151 kg N ha–1 in production fields. As straw-strength improves through advances in hybrid development, greater yield potential can be realized with higher PF-N rates as shown in the current research. Nitrogen applications made at PE increased rice grain yield for both cultivars on silt loam soils and increased whole milled rice for both cultivars on clay soils. When near-maximum grain production is sought, that is, higher PF-N rates, PE-N applications may aid in reducing lodging by minimizing catabolism of structural proteins in vegetative matter.


   ACKNOWLEDGMENTS
 
The authors express their sincere appreciation to the Rice Agronomy support staff from Mississippi State University—DREC and LSU AgCenter—RRS.

All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher.


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





This Article
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Right arrow Articles by Walker, T. W.
Right arrow Articles by Harrell, D. L.
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PubMed
Right arrow Articles by Walker, T. W.
Right arrow Articles by Harrell, D. L.
Agricola
Right arrow Articles by Walker, T. W.
Right arrow Articles by Harrell, D. L.
Related Collections
Right arrow Rice
Right arrow Nitrogen
Right arrow Hybrid Approaches
Right arrow Plant Nutrition
Right arrow Soil Fertility and Productivity

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