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© 2006 Plant Management Network.
Accepted for publication 22 March 2006. Published 23 May 2006.

Ratoon Rice Response to Nitrogen Fertilizer

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

Corresponding author: Jason A. Bond. jbond@agcenter.lsu.edu

Bond, J. A., and Bollich, P. K. 2006. Ratoon rice response to nitrogen fertilizer. Online. Crop Management doi:10.1094/CM-2006-0523-02-RS.

Abstract

Field research was conducted for 2 years to determine the N fertilizer application rate producing maximum ratoon rice grain yields. The long-grain rice cultivars Cheniere, CL161, Cocodrie, and Cypress were grown using a delayed-flood, drill-seeded production system. Immediately following harvest of the main crop, N fertilizer at rates of 30, 60, 90, or 120 lb/acre was applied as urea. No ratoon rice lodging was observed in any site-year at any N fertilizer application rate. Ratoon days to 50% heading was delayed 1 day when the N fertilizer application rate was increased from 60 to 90 or 120 lb/acre. Ratoon rough rice yield increased significantly from 2390 to 2710 lb/acre as the N fertilizer application rate increased from 30 to 90 lb/acre, but increasing the N fertilizer application rate from 90 to 120 lb/acre did not improve ratoon rough rice yields. No ratoon rice lodging was observed in any site-year at any N fertilizer application rate. In this study, the N fertilizer application rate producing maximum ratoon rice yields in the Gulf Coast area of the United States was 90 lb/acre.

Introduction

Over 3.2 million acres of rice (Oryza sativa L.) were planted in the United States in 2005 with production concentrated in Arkansas, California, Louisiana, Mississippi, Missouri, and Texas (13). While the rice acreage in the United States is small compared with that of other crops such as corn (Zea mays L.) or soybean [Glycine max (L.) Merr], rice is an extremely important crop in areas of the southeastern United States, especially in Louisiana and Arkansas, which accounted for 65% of the total United States rice acreage in 2005.

Increasing rice grain yields per unit of area is one approach to improving total rice production (17). Ratooning, the practice of harvesting grain from tillers originating from the stubble of a previously harvested crop (main crop), enhances rice grain yields without increasing land area (12) because it provides higher resource-use efficiency per unit of land area and per unit of time (17).

Research indicates that ratoon rice productivity is influenced by N fertilization (1,12,19). Bahar and De Datta (1) reported ratoon rice grain yield increases of 450 lb/acre as the rate of N applied to the ratoon crop increased from 0 to 54 lb/acre. Ratoon rice grain yields of both ‘Labelle’ and ‘Lebonnet’ increased with increasing N applied to the ratoon crop (12).

Rice has been ratooned in the Gulf Coast areas of Florida, southwest Louisiana, and Texas since the early 1960s (9), but research focused on improving recommendations for ratoon rice in these areas is limited. Current Louisiana recommendations for ratoon rice production suggest application of N at 75 to 90 lb/acre immediately following main-crop harvest if harvest occurs prior to August 15 and establishment of the ratoon-crop flood immediately following N fertilization (16). For ratoon rice production in Texas, recommendations for reflood timing and N fertilization are based on soil type (10). Research addressing management of ratoon rice is vital to improving total rice production in the rice-growing areas of the Gulf Coast. The objective of this research was to determine the N fertilizer application rate producing maximum ratoon rice grain yields.

Two Locations, Four Cultivars, and Four Ratoon N Rates

Experiments to determine the ratoon rice response to N fertilizer application rate of four rice cultivars were conducted in 2003 and 2004 at the Louisiana State University AgCenter Rice Research Station near Crowley, LA, and at an on-farm site near Lake Arthur, LA. Soils at both sites were a Crowley silt loam soil (fine montmorillinitic, thermic Typic Albaqualf). Crowley silt loam is the most common soil type in the rice-growing area of southwestern Louisiana. Results from soil tests taken each site-year are summarized in Table 1. Soil analysis was performed by the Louisiana State University Soil Testing and Plant Analysis Laboratory. A summary of procedures used can be found at the laboratory's website.

Table 1. Chemical properties of soil at field sites.

The long-grain rice cultivars Cheniere, CL161, Cocodrie, and Cypress were drill-seeded on 24 March 2003 and 2004 at Crowley, and 27 March 2003 and 23 March 2004 at Lake Arthur, at a seeding rate of 100 lb/acre and a depth of 0.75 inch. Agronomic characteristics and genetic background information of the rice cultivars are shown in Table 2. 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 (11). Individual plots consisted of 12 rows measuring 25 feet in length at Crowley and 12 rows measuring 20 feet in length at Lake Arthur. Phosphorus and potassium were applied based on soil test results at a rate of 30 and 60 lb/acre, respectively, prior to tillage in the spring. Nitrogen was applied to the main crop at 165 lb/acre as urea immediately prior to flood establishment. 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. Main-crop rice was harvested with a small-plot combine at a moisture content of approximately 20% using an 18- to 24-inch cutting height. Main crop harvest dates were 30 July 2003, and 4 August 2004, at Crowley and 6 August 2003, and 9 August 2004, at Lake Arthur.

Table 2. Agronomic characteristics and genetic background of rice cultivars evaluated^x.

 ^x The data and information were obtained from Steve Linscombe and Xueyan Sha, Louisiana State University AgCenter Rice Research Station, Crowley, LA.

 ^y Pedigrees are represented by the parent lines with the orders of crosses indicated by slashes: "/" = first cross; "/" = second cross; and /3/ = third cross.

 ^z CL161 is an induced mutant of the cultivar Cypress.

Experimental design was a randomized complete block with a factorial arrangement of four rice cultivars and four ratoon N fertilizer application rates with four replications. Nitrogen fertilizer at rates of 30, 60, 90, or 120 lb/acre was applied as urea immediately following main-crop harvest and before flooding of ratoon rice. The ratoon flood was established 1 day following N fertilizer application. Ratoon days to 50% heading was determined by calculating the time period from main-crop harvest until 50% of rice had visible panicles. Lodging of ratoon rice plants was visually estimated on a scale of one (erect) to nine (prostrate). At maturity, ratoon rice was harvested with a small-plot combine at a moisture content of approximately 20%. Ratoon rice harvest dates were 21 October 2003, and 4 November 2004, at Crowley and 5 November 2003 and 8 November 2004 at Lake Arthur. Percent grain moisture was measured and rough rice yield was adjusted to 12% moisture content.

All data were subjected to the Mixed Procedure (18), with locations and years being used as random-effect parameters testing all possible interactions of cultivar and N fertilizer application rate. Years, locations, replications (nested within years), and all possible interactions containing these effects were considered random effects; all other variables (rice cultivar and N fertilizer application rate) were considered fixed effects. Considering year or combination of year and location as environmental or random effects permits inferences about treatments to be made over a range of environments (5,8). A similar statistical approach has been successfully used by other researchers (4,8,15). 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.

Ratoon Rice Maturity and Grain Yield

Main-crop rough rice yields were estimated across site-years at 8180, 8040, 8240, and 8170 lb/acre for Cheniere, CL161, Cocodrie, and Cypress, respectively. Furthermore, no lodging of ratoon rice was observed in any site-year. Analysis of the interaction between cultivar and ratoon N fertilizer rates was not significant for ratoon days to 50% heading (P = 0.39) or ratoon rough rice yield (P = 0.25). The main effect of cultivar averaged across N fertilizer rate was not significant for ratoon days to 50% heading (P = 0.14) or ratoon rough rice yield (P = 0.88). Therefore, data in Table 3 are presented as the main effect of N fertilizer rate averaged across cultivar.

Table 3. Effect of N fertilizer rate on ratoon days to 50%
heading and rough rice yield at Crowley and Lake Arthur,
LA, in 2003 and 2004.

 ^x Means followed by the same letter in a column are not
significantly different at the 5% level.

Increasing the N fertilizer rate from 30 to 60 lb/acre or from 90 to 120 lb/acre had no effect ratoon days to 50% heading (Table 3). Increasing the N fertilizer rate from 60 to 90 lb/acre delayed ratoon days to 50% heading by 1 day. While the influence of N fertilizer rate on ratoon days to 50% heading was slight, the N fertilizer rate had a significant effect on ratoon rough rice yield. As the N fertilizer rate increased from 30 to 90 lb/acre, the ratoon rough rice yield increased significantly from 2390 to 2710 lb/acre (Table 3). Increasing the N fertilizer from 90 to 120 lb/acre did not improve ratoon rough rice yields.

Although the delay in ratoon maturity as N fertilizer rate increased from 60 to 90 lb/acre was significant, a 1-day delay in maturity would probably not influence harvestability or ratoon rice yields. However, longer delays in ratoon maturity could have some practical implication. In areas of the United States where rice is ratooned, the growing season prior to the onset of unfavorable temperatures is not long enough in every year to allow maturation of the ratoon grain. A decline in temperature and daylength as the ratoon crop is developing could produce negative impacts on pollination, grain filling, ratoon rough rice yield and milling quality. Furthermore, the months of September and October, when the ratoon crop is developing, are also the months when the production area is most susceptible to tropical weather systems. Therefore, delays in ratoon maturity of 3 to 4 days could result in significant yield loss in years when low temperatures or tropical weather systems occur before the ratoon crop is fully developed.

Cultivars evaluated in this research responded similarly to N fertilizer rate. Although the similar pedigrees of these cultivars (Table 2) may explain the consistency in their response to N fertilizer rate, these four cultivars were chosen because they were either grown on large acreage in Louisiana or were newly-released cultivars. When this research was initiated in 2003, Cocodrie and Cypress represented 83% of the rice acreage in Louisiana (J. K. Saichuk, personal communication). CL161 acreage in Louisiana increased from approximately 11000 acres in 2003 to over 100,000 acres in 2005. Cheniere was released in 2004 and was planted on 10% of Louisiana rice acreage.

The response to N fertilizer rate reported here was similar to that reported by Bahar and De Datta (1) and Mengel and Wilson (12). These researchers also reported increases in ratoon rice yields with increasing N fertilizer rate. Bahar and De Datta (1) reported the optimum N fertilizer rate for ratoon rice production to be 54 lb/acre but speculated that N fertilizer applied at panicle initiation of the main crop may have depressed the optimum rate of N fertilizer required for ratoon rice production. Mengel and Wilson (12) reported an N fertilizer application rate of 80 lb/acre followed by immediate flooding produced highest ratoon rice yields.

Rice cultivars commonly grown in the United States require and respond to large amounts of N (3,14,20). Although N applications are essential to produce acceptable rice grain yields, excessive applications of N can have negative results (20). Increased vegetative growth, lodging, disease damage, delayed maturity, and reduced grain yields of lower quality can occur if N applications are made at unnecessary rates or to rice at the wrong growth stage (6,7,20). These adverse effects of excessive N fertilization would also be manifested in ratoon rice production, so the determination that increasing the ratoon N fertilizer application rate from 90 to 120 lb/acre did not improve ratoon grain yield was an important finding of the current research.

As with the current research, research by Mengel and Wilson (12) was conducted at the Louisiana State University AgCenter Rice Research Station near Crowley, LA. However, these researchers examined the ratoon N fertilizer response of conventional-height cultivars Labelle and Lebonnet, which have now been replaced with higher-yielding, semidwarf cultivars. Cultivars tested in the current research are all semidwarf cultivars with high yield potential. These newer semidwarf cultivars respond differently to inputs than the older conventional-height cultivars, so it would be expected that the N fertilizer rate producing maximum ratoon rice production would be higher than that observed for older, conventional height cultivars.

In rice-growing areas along the Gulf Coast of the United States, a ratoon rice harvest is valuable to a producer’s income because it increases total production on a given area with a limited amount of additional input (2). Verification that the N fertilizer rate producing maximum ratoon rough rice yields for semidwarf cultivars was 90 lb/acre led to an increase in the recommended ratoon N fertilizer rate in Louisiana (16). However, the income attained from the additional harvest must offset the added input costs of ratoon production. N fertilizer is an expensive input for crop production. Decisions about the appropriate application rate of N fertilizer should be field-specific and based on a balance of the cost of N fertilizer and the income realized from the increased yield resulting from a higher N fertilizer rate.

Acknowledgment

The authors thank the staff of the Louisiana State University AgCenter Rice Research Station for their assistance in this research. The Louisiana Rice Research Board provided partial funding for this research.

Published with the approval of the Director of the Agricultural Experiment Station, Louisiana State University AgCenter, manuscript number 05-61-0462.

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