C. A. Beyrouty

Nutrient uptake relationship to root characteristics of rice

Data on root parameters and distribution are important for an improved understanding of the factors influencing nutrient uptake by a crop. Therefore, a study was conducted on a Crowley silt loam at the Rice Research and Extension Center near Stuttgart, Arkansas to measure root growth and N, P and K uptake by three rice (Oryza sativa L.) cultivars at active tillering (36 days after emergence (DAE)), maximum tillering (41 DAE), 1.25 cm internode elongation (55 DAE), booting (77 DAE) and heading (88 DAE). Soil-root core samples were taken to a depth of 40 cm after plant samples were removed, sectioned into 5 cm intervals, roots were washed from soil and root lengths, dry weights and radii were measured. Root parameters were significantly affected by the soil depth × growth stage interaction. In addition, only root radius was affected by cultivar. At the 0- to 5-cm soil depth, root length density ranged from 38 to 93 cm cm-3 throughout the growing season and decreased with depth to about 2 cm cm-3 in the 35- to 40-cm depth increment. The increase in root length measured with each succeeding growth stage in each soil horizon also resulted in increased root surface area, hence providing more exposed area for nutrient uptake. About 90% of the total root length was found in the 0- to 20-cm soil depth throughout the season. Average root radius measured in the 0- to 5-cm and 35- to 40-cm depth increments ranged from 0.012 to 0.013 cm and 0.004 to 0.005 cm, respectively throughout the season. Total nutrient uptake by rice differed among cultivars only during vegetative growth. Differences in total nutrient uptake among the cultivars in the field appear to be related to absorption kinetics of the cultivars measured in a growth chamber study.

Root growth and distribution of two short-season rice genotypes

Root growth dynamics of lowland rice (Oryza sativa L.) throughout the growing season are poorly understood. A field experiment was conducted in 1987 to compare root growth and distribution of two rice genotypes at two Arkansas locations on soils with different physical and chemical properties. Two genotypes, ‘Bond’ and an experimental line (RU8701084), were grown on a Captina silt loam (Typic Fragiudults) at Fayetteville, AR, and on a Crowley silt loam (Typic Albaqualfs) near Stuttgart, Ar. Plots contained minirhizotrons oriented at a 45° angle and extended 55 cm (Captina) and 40 cm (Crowley) vertical to the soil surface. Root measurements were taken several times during the season at specific growth stages. Plant height and tiller number were taken at 9 dates at Fayetteville up to physiological maturity. In general, root length (RL) and root length density (RLD) were greater on the Captina soil. Genotypes at both locations reached maximum root growth rates between active tillering and panicle initiation (PI) and maximum RL by early reproduction. Total RL were similar between genotypes on the Captina. However on the Crowley, the mean RL for Bond between the period of early booting and flood removal was an average of 54% greater than for RU8701084. During early reproductive growth at both locations RL plateaued, but then declined during the grain filling process. There was a trend for RU8701084 to contain a greater percentage of its total RL in the top 20 and 10 cm of soil on the Captina and Crowley, respectively, while Bond tended to be a deeper rooted genotype. Bond had a greater RLD at the 20–30 cm depth increment on the Crowley, which contributed to the greater RL. Less than 15% of the total RL of either genotype was measured below 30 cm on the Crowley. In contrast, nearly 25% of the total RL was found at the 30–40 cm depth increment on the Captina. Results showed that rice root growth varied between soils, that root distribution patterns differed between genotypes, and that patterns of root growth changed with changes in plant development.

Nutrient uptake by rice in response to water management

Abstract All rice (Oryza sativa L.) production in the United States utilizes flood irrigation. Yet, depletion of the aquifer in eastern Arkansas may necessitate the adoption of rice production practices that reduce water inputs. Field studies were conducted to evaluate reductions in the duration of floodwater application on nutrient uptake by lowland irrigated rice. Three water management treatments, (i) recommended application of a flood applied at the 4‐ to 5‐leaf stage of development (normal flood), (ii) a delay in the application of the flood until panicle differentiation (delayed flood), and (iii) full‐season intermittent flush irrigation (flush irrigated), were imposed on the cultivar Tebonnet’ grown on a Crowley silt loam (Typic Albaqualfs). Nitrogen (N) was applied as a recommended three‐way split to all treatments. Uptake and tissue concentration of N, phosphorus (P), potassium (K), zinc (Zn), iron (Fe), and manganese (Mn) were determined. Rice subjected to normal flooding consistently responded ...

Nitrogen, phosphorus, and potassium influx kinetic parameters of three rice cultivars

Abstract Information about the nutrient absorption properties of rice (Oryza sativa L.) roots can be used to predict nutrient uptake and to determine levels needed in the soil to supply nutrients rapidly enough to the root surface to minimize deficiencies. A study was conducted to measure the maximum influx (Imax), the respective Michaelis constants (Km), and the minimum solution concentrations necessary for uptake (Cmin) of nitrogen (NH4+), phosphorus (PO43‐), and potassium (K+) by three rice cultivars (Katy, Lemont, and Mars). Single plants of a given cultivar were transplanted into a nutrient solution containing a low concentration of a given element. The solution was sampled continuously for 10 to 15 h, following which roots were harvested and root surface areas determined. The three influx parameters for each cultivar and element were calculated from the individual nutrient depletion curves. The only effect of cultivar was found for the Imax of K+. Potassium Imax for Katy was 42% lower than for Lemon...

Rice responses to changes in floodwater and N timing in southern USA.

Abstract Delayed application and/or early draining of floodwater to lowland irrigated rice (Oryza sativa L.) should allow producers in southern USA more time for ground application of chemicals while reducing potential hazards from aerial applications and conserving water. Two field studies were conducted to evaluate growth and yield responses of “Tebonnet”, “Alan”, and “Texmont” rice to reduced flood duration and altered N management. Depending upon the study, treatments consisted of normal (four- to five-leaf stage) or delayed timing of flood application in combination with recommended or earlier-than-recommended draining of the floodwater, and full-season flush irrigation. Nitrogen was either applied once at the four- to five-leaf stage or as a three-way split with normal- or earlier-than-recommended timing. Flush irrigation reduced shoot and root growth and yield of rice as compared to normal flood while delayed-flood irrigation reduced shoot dry weight but had no effect on root length density or grain and head-rice yields. Nitrogen uptake was greater with a single preflood application of N than with a three-way split application. Yields were not affected by N management or earlier-than-recommended draining of the floodwater. These data indicate that the duration of floodwater application currently practiced in rice production in southern USA may be reduced without sacrificing grain yield or quality.

Root development of bermudagrass and tall fescue as affected by cutting interval and growth regulators.

A study was conducted to characterize changes in bermudagrass (Cynodon dactylon [L.] Pers.) and tall fescue (Festuca arundinacea Schreb.) root development over time and with depth, and to determine the effects of defoliation interval and chemical seedhead suppression on root and shoot growth. Field plots were established on a fine-silty, mixed mesic Typic Fragiudult soil in Fayetteville, AR, USA, and each plot contained three minirhizotrons (plexiglass observation tubes) to a depth of 40 cm. Images of roots in 10-cm depth increments were periodically videorecorded, and total root length (RL) and root length density (RLD) were measured with a computer-interfaced tracing probe. Treatments consisted of two cutting intervals, 3 and 6 weeks, and two plant growth regulator (PGR) treatments, an untreated control and either 300 g ha-1 mefluidide on tall fescue in early spring of both years or 10 g ha-1 each of metsulfuron methyl (MSM) and sulfometuron methyl (SMM) applied in late May of both post-establishment years. Data were analyzed separately for the establishment period (planting to the first date of PGR application) and the subsequent post-establishment period. Bermulagrass exhibited a two-stage root establishment pattern characterized first by minimal root development in conjunction with stolon proliferation and soil surface colonization, followed by accumulation of total RL over two subsequent forage production seasons. There was a net accumulation of root mass during the winter dormancy period of 1986–87. Total RL of tall fescue peaked one and a half years after planting. Cutting interval had no influence on RL and RLD. Application of a PGR did not affect RL but did alter RLD of both species. Application of mefluidide to tall fescue stimulated RLD 64 days after application, whereas bermudagrass RLD was retarded by MSM and SMM up to 50 days after application. Trends in root growth did not closely follow patterns of shoot growth.

Water management and location effects on root and shoot growth of irrigated lowland rice

Abstract In the United States rice (Oryza sativa L.) is entirely flood irrigated. Delaying the application of the floodwater beyond the recommended time is practiced by some Arkansas producers and may (with supplemental rainfall) potentially reduce the water inputs required to produce a crop. Water stress, however, may affect root growth characteristics which could impact fertility management decisions relative to continuous flood culture. Therefore a field study was initiated to identify the responses of root and shoot growth and yield to water management and location. Two water management treatments were imposed on the ‘Tebonnet’ cultivar, i) normal water management where a flood was applied at the four‐ to five‐leaf stage (continuous flood), and ii) flood delayed (but with supplemental irrigation) until 1.25 cm internode elongation. Studies were located on two soils in eastern Arkansas, a Sharkey clay and Crowley silt loam in 1988 and 1989. The floodwater was removed from plots approximately 10 d befor...

EFFECTIVENESS OF PHOSPHOROAMIDES IN RETARDING HYDROLYSIS OF UREA SURFACE-APPLIED TO SOILS WITH VARIOUS pH AND RESIDUE COVER1

A field experiment compared the ability of several phosphoroamide compounds to retard urea hydrolysis on a fallowed notill (NT) and conventionally tilled (CT) silt loam soil (pH 5.70). Treatments consisted of urea prills (200 kg N ha-1) with and without inhibitors (4.0 kg ha-1) and a no-fertilizer check. Fertilizers were surface-applied to 10-cm-diameter polyvinyl chloride (PVC) cylinder microplots partially embedded in the soil. Duplicate microplots were removed at intervals after fertilization and analyzed for the quantity of urea remaining. Results indicate that, of the compounds tested, phenyl phosphorodiamidate (PPD) most effectively inhibited urea hydrolysis. Addition of PPD reduced the initial (first 4 to 10 d after fertilization) rate of hydrolysis by 60 to 70% in three of four trials conducted. A laboratory study conducted on a soil at two contrasting initial pH values (5.6 and 7.4) showed that PPD was more effective in the acidic than in the alkaline soil. Two other inhibitors (UI4 and UI5) retarded hydrolysis to a greater degree than did PPD in the alkaline soil. In the same laboratory study phosphoroamide (UI6), not tested in the field, was found to be least effected by soil pH and showed promise as a urease inhibitor in both acidic and alkaline soils. Field and laboratory studies indicate that urea was hydrolyzed 2.3 to 3 times faster when added to corn-residue-covered surfaces than to bare soil. This finding suggests that the residue contained high levels of urease activity.

RELATING SOIL TEST P TO P UPTAKE BY PADDY RICE

In Arkansas, the Mehlich-3 extraetant is used in the determination of soil test P for both upland and lowland crops. However, this technique does not consistently predict a response by paddy rice (Oryza sativa L.) to P fertilization. The objective of this research was to relate soil test P determined by four extractants to P uptake by paddy rice grown on two rice-producing soils. The soils in this study were a Crowley silt loam and two Hillemann silt loam samples collected from fields where P deficiencies in rice were observed the previous summer. Rice was grown on these soils in the greenhouse at fertilizer rates of 0, 5, 10, 20 and 40 mg P kg-1. Plant uptake and tissue concentrations of P were measured and related to soil test P extracted by Mehlich-3, Bray-1, Olsen, or ion exchange resin at 0, 24, 31, and 124 days after flooding (DAF). The Crowley had the highest soil test P obtained with all extractants at all flooding dates compared with the two Hillemann soil samples. Mehlich-3 and Bray-1 extractants consistently gave higher soil test P values on the Crowley soil than did Olsen and resin extractants. Only the resin showed a consistent correlation between soil test P measured at 0 DAF and % P in shoot and total P uptake measured at 24, 31, and 124 DAF. This correlation was improved when P uptake was related to soil test P measured on anaerobic soils. Although Mehlich-3 is convenient for soil test laboratories, the resin appears to be a more appropriate extractant to estimate plant available P for paddy rice.

Nutrient supplying capacity of a paddy rice soil

Abstract The availability of a nutrient is related to the soil solution concentration of the nutrient, soil buffer power and the effective diffusion coefficient. A field experiment was conducted at the Rice Research and Extension Center, near Stuttgart, Arkansas to determine these parameters for ammonium (NH4), phosphorus (P), and potassium (K) under the flooded conditions of paddy rice (Oryza sativa L.) and to use these parameters to calculate the relative importance of mass flow and diffusion to nutrient movement to rice roots. Three rice cultivars were grown on a Crowley silt loam. Saturated soil samples were taken from the 0‐ to 40‐cm depth at active tillering [36 days after emergence (DAE)], maximum tillering (41 DAE), 1.25 cm internode elongation (55 DAE), booting (77 DAE) and heading (88 DAE). Labile and solution concentrations, buffer power and effective diffusion coefficients of NH4, P, and K were determined on 5 cm depth increments. In general, labile and solution concentrations of NH4, P, and K...