Boron fertilization of bentgrass.
Grass response to B fertilization has been less well documented. Greenhouse studies have examined the growth response of Kentucky bluegrass (Poa pratensis L.), creeping bentgrass, and tall fescue (Festuca arundinacea Schreb.). Addition of B at rates of 0.8 or 4.8 mg [kg.sup.-1] was not detrimental to germination and establishment, as germination of Kentucky bluegrass and creeping bentgrass increased 15 to 20% when compared with zero-B control treatments (Oertli et al., 1961). Tall fescue, creeping bentgrass, Kentucky bluegrass, perennial ryegrass (Lolium perenne L.), bermudagrass [Cynodon dactylon (L.) Pers.], and zoysiagrass (Zoysia japonica Steud.) were grown in nutrient solution containing 10 mg [kg.sup.-1] B. Leaf tip burn due to B toxicity was observed, with greater injury occurring on the cool season grasses. However, even with high concentrations of plant B, little decline in plant vigor was observed, and frequent clipping removed most visible tip necrosis (Oertli et al., 1961). In another greenhouse study, Kentucky bluegrass maintained at high or low levels of general fertility was fertilized with B at rates of 1.7 or 8.4 kg B [ha.sup.-1]. In the low-fertility plots, bluegrass receiving supplemental B had increased color, growth, and dry matter yield when compared with plots receiving no B (Deal and Engel, 1965). In the high-fertility plots, application of 8.4 kg B [ha.sup.-1] increased turf growth during the first 6 wk of the study, but did not affect growth for the remaining 7 wk of the study. All growth effects were most pronounced in the first 5 wk of the study, and in later weeks, tip burn of leaves was observed, similar to the study of Oertli et al. (1961). It was concluded that in turf with low fertility, the 1.7 kg B [ha.sup-1] rate temporarily increased turf green color, while in well-fertilized turf the 8.4 kg B [ha.sup.-1] rate was toxic, when examined during the entire 13 wk of the study (Deal and Engel, 1965).
Boron fertilization research with warm-season grasses has largely focused on forage-type bermudagrass. The 3-yr average yield of Coastal bermudagrass was increased by the yearly application of B at 2.2 kg B [ha.sup.-1] (Spooner and Huneycutt, 1983). In another field study, B was applied yearly at 0, 1.1, 2.2, or 4.4 kg B [ha.sup.-1] to seven different bermudagrass cultivars. When averaged across all grasses, dry matter yield was increased when B was applied at 2.2 kg [ha.sup.-1]. However, the effect was significant in only two of seven cultivars. It was concluded that the variable data collected from the 4-yr study would not support a general recommendation of supplemental B on forage-type bermudagrasses (Monson and Gaines, 1986).
Of the B research conducted with turfgasses, none of the published work was conducted under field conditions (Oertli et al., 1961; Deal and Engel, 1965; Lee et al., 1996). Typically, B toxicity symptoms were most evident at higher rates of B fertilization, when grasses were grown in a B-amended nutrient solution (Oertli et al., 1961; Lee et al., 1996). Positive growth responses were observed at lower rates of B fertilization in soil or soil/peat mixes, especially if background soil fertility was also low (Deal and Engel, 1965).
Boron will leach in sandy soils (Hull, 2002), and possible downward movement in sand-based putting greens could affect B fertilization needs for turf. There is no data examining B fertilization of putting greens in field situations, and no research which examines B fertilization of recently introduced bentgrass cultivars. Moreover, micronutrient fertilization is a growing marketing tool in the turf industry, and additional data about micronutrient fertilization of turf is needed to help golf course superintendents decide if supplemental B fertilization is necessary. The objective of this research was to examine the effect of B fertilization on quality, shoot density, and rooting of cultivars of creeping bentgrass in both a greenhouse and field study.
MATERIALS AND METHODS
In December 1998 a greenhouse experiment was initiated at the Plant Science Research Center, Auburn, AL. Three creeping bentgrass cultivars ('SR1020', 'Crenshaw', and 'Dominant') were seeded into 2.5-cm-diam. conetainers filled with a 15% reed sedge peat/85% sand greensmix to an approximate bulk density of 1.5 g [cm.sup.-3]. When the bentgrass seedlings were [approximately equal to] 3 wk old, seedlings in the conetainers were thinned to one seedling per conetainer. To lessen experimental variability, an experimental unit was the average of data collected from a single row of 10 individual conetainers. This average was considered one replication of a cultivar/B rate treatment combination. Cultivar/B rate treatments were arranged in the greenhouse in a completely randomized design. There were four replications of each bentgrass cultivar/B rate treatment. Thus, with three bentgrass cultivars and 5 B rates there were 15 treatments in the study, each replicated four times, a total of 600 conetainers in the study.
Boron treatments were weekly applications of B (Boric acid, [H.sub.3]B[O.sub.3]) applied at 0.0, 0.5, 1.0, 2.0, and 3.0 mg [kg.sup.-1] B. Boron treatments were applied weekly in 30 mL (per conetainer) of a B-depleted Hoaglands solution, starting immediately after the conetainers were thinned to one seedling (3 wk of growth). Seedlings were maintained for an additional 8 wk, after which aboveground shoot growth was removed. Wet and dry weight of shoot growth was determined. Harvested roots were washed though a sieve to remove sand and peat, and dry weight determined.
Beginning in March 1999, a field study was initiated at the Auburn University Turfgrass Research Unit on a native soil (Marvyn loamy sand; fine-loamy, kaolinitic, thermic Typic Kanhapludult) bentgrass putting green. The green had been established in the fall of 1997 with four replicate blocks of the creeping bentgrass cultivars: 'Penn G2', 'L-93', 'Crenshaw', 'Penncross', 'Penn A2', 'Penn G6', 'Penn G1', 'SR1020', and 'Dominant'. Each bentgrass cultivar main block was 3.7 by 2.1 m in size. Cultivar main blocks were split into four strips of 0.9 by 2.1 m, each receiving one of four yearly B fertilizer rates (0, 0.55, 1.1, or 2.2 kg B [ha.sup.-1] [yr.sup.-1]), split into 12 monthly applications. Boron source was sodium borate (Solubor, 20.5% B, U.S. Borax, Inc., Valencia, CA). Boron treatments were applied with a backpack C[O.sub.2]--powered sprayer in a 468 L [ha.sup.-1] spray volume. Boron was applied at the beginning of each month beginning in March 1999 and continued until June 2001.
The research area was maintained uniformly as a bentgrass putting green with all plots mowed daily at a height of 4 mm using a triplex greens mower. Additional plot maintenance included vertical mowing (2.5-cm depth) and topdressing during the months of September, December, and February, and high-pressure water injection during the months of May, June, and July. Plots were core aerified (10-mm-diam. hollow tine) and sand topdressed in October of each year, with cores removed. Fertilizer was applied with B-depleted materials (N[H.sub.4]N[O.sub.3], 34-0-0; triple super phosphate, 0-46-0; [K.sub.2]S[O.sub.4], 0-0-50) to supply N at 0.01 g [m.sup.-2] [mo.sup.-1], and P and K were applied according to soil-test recommendations (taken four times each year). Typical yearly soil tests for the research area reported soil-test P at 112 kg [P.sub.2][O.sub.5] [ha.sup.-1] (very high), K at 170 kg [K.sub.2]O [ha.sup.-1] (high), and a pH of 6.2. Irrigation was applied as needed to supply 2.5 cm water per week.
Collected data included monthly clipping yield and relative turf quality. Clipping data was obtained by mowing a 0.45-by 2-m strip in the middle of each plot, drying the clippings in a forced-air oven for 48 h, and recording dry weight. Relative turf color was recorded on a 1- to 9- scale, with a score of 1 being brown turf, a 9 dark green, and a 5 as a satisfactory green color. In June of 2000 and 2001, a subsample of collected clippings was dry-ashed, extracted, and analyzed for B content via ICP (inductively coupled plasma emission spectroscopy) analysis (Adams et al., 1994). In June 2000 and 2001, five 2.5-cm-diam. plugs were removed randomly from each plot, and compressed thatch depth was recorded. An average thatch depth for each plot was obtained by averaging the five subsamples. In June 2001, an additional five 2.54-cm-diam. turf plugs were removed from the control (0 B), low (0.55 kg B), and high (2.2 kg B) treatments. Individual shoots from these samples were separated and counted to obtain shoot density readings for each sample. The five subsamples were averaged and reported as an average shoot density for each plot.
RESULTS AND DISCUSSION
There was not a significant B rate x bentgrass cultivar interaction for wet or dry weight of bentgrass shoots. The main effect of cultivar was significant, with both wet and dry weights of bentgrass shoots varying because of cultivar. The average wet and dry weight of Dominant was 1.33 and 0.41 g per conetainer, respectively, significantly greater than the shoot weights of Crenshaw (1.19 and 0.37 g, wet and dry, respectively) or SR-1020 (1.13 and 0.33 g). There was no difference in shoot wet or dry weight of Crenshaw or SR-1020. Dry root weight of the bentgrass cultivars was unaffected by cultivar.
As B rate increased, the dry weight of bentgrass shoots increased (Fig. 1). Although not significant, shoot wet weight followed a similar trend with wet weight increasing as B rate increased, but variability within treatments was high and the regression equation was not significant. Root dry weight was opposite the trend observed with shoot weights, as root weight generally decreased as B rate increased. However, this relationship was not significant, as determined by linear regression (Fig. 1). Root dry weight was greatest at the 0.5 mg [kg.sup.-1] B rate, and decreased thereafter as B rate increased.
[FIGURE 1 OMITTED]
Increases in dry matter production due to B application have been observed in Kentucky bluegrass (Deal and Engel, 1965) and forage bermudagrass production (Monson and Gaines, 1986). In a greenhouse study of micronutrient toxicity in Kentucky bluegrass, B rates from 5.4 to 10.8 mg [kg.sup.-1] B did not affect dry weight of bluegrass shoots, although B toxicity symptoms were apparent at the lowest rate of 5.4 mg [kg.sup.-1] B. As B concentrations increased from 21.6 to 129.7 mg [kg.sup.-1] B, shoot weight of Kentucky bluegrass decreased (Lee et al., 1996). In our study there were no visible signs of B toxicity on the leaf tips of the bentgrass, as the lower B concentrations applied may not have created toxic conditions. Increases in dry matter production at lower rates of B addition may have been missed in the study by Lee et al., as their lowest B rate was similar to the highest rates used in this study.
Boron fertilizer rates used in this study (0 to 2.2 kg B [ha.sup.-1]) were based on B experiments previously published. For example, Monson and Gaines (1986), in a similar geographic region, used rates of 0 to 4.4 kg B [ha.sup.-1] for their forage bermudagrass study. Other cool season turfgrass research used a B rate of 1.7 kg B [ha.sup.-1] (Deal and Engel, 1965). Last, the selected B rates bracket B recommendations (0.56 to 1.7 kg B [ha.sup.-1]) for B-responsive crops in Alabama (Adams et al., 1994).
There were 16 separate clipping collections taken during the 2 yr of the study. At no time was there a significant B rate x cultivar interaction, and at no time did the rate of B fertilization affect dry weight of clippings (Table 1). This differs from that observed in the greenhouse trial, where dry shoot growth increased as B rate increased. The field study was conducted on a loamy sand soil (80% sand) with a sand content equal to that found in many sand/peat-based putting greens. However, the clay and organic matter content of the native soil green may have reduced the likelihood of a B response.
In other field research, application of B at 8.4 kg [ha.sup.-1] increased dry matter production for the first 6 wk of the study (Deal and Engel, 1965). During Weeks 7 though 13 of the study, however, signs of B toxicity were evident and turf growth was reduced. Thus, the long-term application of B at 8.4 kg [ha.sup.-1] was toxic to the Kentucky bluegrass turf. In a nutrient solution study, dry matter production of Kentucky bluegrass was reduced at B rates > 2 mM B (21.6 mg [L.sup.-1]) (Lee et al., 1996). In another field study, application of B at 2.2 kg [ha.sup.-1] [yr.sup.-1] increased dry matter production in bermudagrass (Monson and Gaines, 1986).
Clipping yield was affected by bentgrass cultivar (Table 1). On 10 of 16 sampling dates Penncross had among the highest clipping yields, and on 6 of those 10 dates Penncross had a significantly higher yield than any other cultivar. Penncross is usually considered a heat-sensitive cultivar, and has been shown to be a bentgrass cultivar with a lower root-to-shoot ratio than heat-tolerant cultivars (Schlossberg and Karnok, 2001; Xu and Huang, 2001). In an extreme heat-stress environment such as central Alabama, it may be that heat-tolerant cultivars such as Crenshaw, SR-1020, or L-93 survive heat by producing less topgrowth and more roots. Penncross may simply continue to produce more clippings throughout the year, as its survival mechanism for heat-stress does not include increased root production. On 10 of 16 sampling dates the heat-tolerant cultivar L-93 (Xu and Huang, 2001) had a lower clipping yield than the heat-sensitive Penncross, possibly because the resources of L-93 had shifted to root production.
Bentgrass cultivars with documented high shoot density (Penn A-2, Penn G-1, Penn G-2, and Penn G-6; [Sweeney et al., 2001]) did not always produce a greater clipping yield than those cultivars considered to have standard shoot densities (Penncross, Crenshaw, and SR-1020; [Sweeney et al., 2001]). Clipping yield of any of the Penn cultivars were similar to each other and to other bentgrass cultivars in the study. With the exception of the Penncross differences discussed above, differences in clipping yield due to cultivar were relatively minor, and varied from sampling to sampling.
Thatch Depth and Shoot Density
No significant B rate x cultivar interaction was observed for thatch depth, nor did the main effect of B rate significantly affect thatch depth (Table 2). There were differences in thatch depth due to cultivar, as cultivars with a higher shoot density (Penn A-2, Penn G-1, Penn G-6) had a greater thatch depth than other cultivars. Penncross, considered a low-shoot density cultivar, had the lowest level of thatch in June 2000, and was one of three cultivars with a low thatch depth in June 2001 (others were Penn G-2 and SR-1020).
Collected shoot data matched the thatch data, as cultivars with the greatest thatch also had the highest shoot density (Penn A-2, Penn G-1, and Penn G-6), and those with lowest thatch had lowest shoot density (Penncross). Shoot density was unaffected by 2 yr of B application, and there was not a significant B rate x cultivar interaction (Table 2). It is not uncommon for Penncross to have low shoot densities, and this result has been shown in other work (Schlossberg and Karnok, 2001; Sweeney et al., 2001).
Boron Concentration and Uptake
There was never a significant B rate x cultivar interaction for B concentration or uptake in either year of the study. In June 2000, B concentration in harvested bentgrass clippings increased quadratically as B rate increased, maximizing at a B application rate of 1.6 kg B [ha.sup.-1] (Table 3). Boron content of harvested bentgrass was unaffected by B rate in 2001. Previous work with B uptake has shown some increase in B concentration in harvested forage with increased rates of B fertilization, but there was no correlation between B concentration and yield (Monson and Gaines, 1986). Another study that examined B uptake by bermudagrass ('Tifway II') used boric acid treated recycled paper as the B source (Wilkinson, 1997). No visual symptoms of B toxicity were observed, and B recovery in plant growth was small (Wilkinson, 1997).
In both years of the study, B concentration in plant tissue was unaffected by cultivar (Table 3). There were differences in B uptake due to cultivar, with the cultivar Penncross having significantly greater B uptake than other cultivars in both years of the study. In both June 2000 and 2001 Penncross had the greatest dry matter production (Table 1), which reflected greater B uptake in those same months.
Monthly color ratings never contained a significant cultivar x B rate interaction, and the main effect of B rate never affected bentgrass color (data not shown). The bentgrass did not demonstrate positive (darker green color) or negative (toxicity symptoms) effects due to B applications. This lack of color response and/or toxicity symptoms has been reported in other field studies, even with rates far higher than applied in this study (Wilkinson, 1997).
There were differences in bentgrass color due to cultivar (data not shown). The most consistent effect was that Penncross had significantly lower color ratings than other cultivars in the study. For example, in June 1999 Penncross received a relative color score of 4.6, significantly lower than the average color score of 6.5 for the other eight cultivars. In April 2000, Penncross received a score of 5.9, significantly lower than the average score of 6.8 for the remaining cultivars. No one cultivar exhibited better color than another throughout the 2 yr of the study. Typically, the cultivar Penn A-2 received the highest color rating, but this was not always significantly better than others.
Application of B fertilizer at rates up to 4.4 kg B [ha.sup.-1] did not affect dry matter production, thatch depth, or shoot density of eight different bentgrass cultivars grown in a loamy sand putting green. In the greenhouse study, shoot dry weight increased as B rate increased. In the field (in one year only), B concentration in bentgrass increased as B rate increased. At the B rates used in this study there were no visual impacts on turf color, and there was no evidence of B toxicity. Results from this study indicate that B fertilization of bentgrass grown on a native soil (loamy sand) putting green did not produce any improvement in color, shoot density, or dry matter production. Boron fertilization of turfgrasses maintained on United States Golf Association-type (high sand) greens might warrant further research.
Table 1. Dry matter production of creeping bentgrass as affected by B rate and cultivar, Auburn, AL, 1999-2001. June July Aug. Sept. 1999 1999 1999 1999 g [m.sup.-2] B rate, kg [ha.sup.-1] 0.0 16.6 9.8 3.9 7.3 0.5 17.7 9.1 4.2 7.1 1.0 16.9 8.5 4.0 7.1 2.0 17.8 9.8 4.1 7.0 Linear ([dagger]) ns ns ns ns Quadratic ns ns ns ns Cultivar A-2 21.9a ([double 10.7ab 3.3c 6.4cd dagger]) G-1 21.3a 11.7a 3.7bc 7.0bc G-6 16.3bcd 10.2abc 3.9bc 5.5d L-93 19.4ab 9.6abc 4.1bc 7.2bc SR-1020 l6.1bcd 9.7abc 4.6ab 8.1ab Dominant 17.2bc 8.7abc 4.4ab 7.4bc Crenshaw 16.1bcd 8.3bc 3.6c 6.6cd G-2 14.6cd 7.2c 3.6c 7.2bc Penncross 12.6d 7.4bc 5.1a 8.8a Oct. Feb. Mar. Apr. May 1999 2000 2000 2000 2000 g [m.sup.-2] B rate, kg [ha.sup.-1] 0.0 11.1 11.5 13.6 7.5 10.3 0.5 11.4 11.2 13.4 8.0 10.2 1.0 11.8 12.0 13.5 8.2 10.4 2.0 11.6 12.2 13.7 8.2 10.3 Linear ([dagger]) ns ns ns ns ns Quadratic ns ns ns ns ns Cultivar A-2 9.6c 9.5a 11.3c 7.1c 8.8d G-1 12.4a 11.7a 13.8ab 7.4c 9.3cd G-6 10.4bc 10.8a 14.3ab 8.7b 10.26c L-93 11.4ab 10.6a 13.6ab 7.4c 10.5b SR-1020 11.1a 11.1a 13.5ab 7.8bc l0.0bc Dominant 11.2a 10.4a 15.1a 8.2bc ll.1ab Crenshaw 10.8abc 9.6a 11.9b 7.7bc 10.5b G-2 12.0ab 9.5a 13.3b 7.8bc 10.3bc Penncross 11.8ab 11.4a 13.8ab 9.7a 10.7a June Aug. Sept. Oct. 2000 2000 2000 2000 g [m.sup.-2] B rate, kg [ha.sup.-1] 0.0 5.9 10.2 17.7 10.0 0.5 5.9 10.0 17.6 10.1 1.0 6.4 10.1 17.6 10.1 2.0 6.1 10.2 17.4 10.2 Linear ([dagger]) ns ns ns ns Quadratic ns ns ns ns Cultivar A-2 5.7b 9.1c 18.2bc 8.9bc G-1 5.2b 9.7bc 14.4d 9.5b G-6 6.1b 10.3b 20.2a 8.5bc L-93 6.0b 10.4b 18.0bc 8.8bc SR-1020 6.1b 10.4b 16.6cd 9.2bc Dominant 5.8b 10.6b 19.1ab 9.1bc Crenshaw 5.5b 9.6bc 16.7cd 7.5c G-2 5.9b 9.5bc 14.7cd 9.1bc Penncross 8.2a 11.7a 17.0cd 11.3a Nov. Dec. June 2000 2000 2001 g [m.sup.-2] B rate, kg [ha.sup.-1] 0.0 10.7 6.8 6.7 0.5 10.8 7.1 7.5 1.0 11.5 6.9 7.2 2.0 11.2 6.8 7.5 Linear ([dagger]) ns ns ns Quadratic ns ns ns Cultivar A-2 9.2bc 4.7c 5.6d G-1 8.4c 5.9b 5.5d G-6 9.9bc 4.8c 5.6d L-93 9.6bc 6.2b 5.8d SR-1020 10.0b 6.7ab 6.1cd Dominant 9.8bc 7.1a 7.3bc Crenshaw 9.7bc 6.0b 6.1cd G-2 10.3b 7.2a 7.5b Penncross 12.7a 7.2a 9.1a ([dagger]) Significance of regression equations fit to the data; ns, not significant. ([double dagger]) Within each sampling date, means separation by Duncan's Mean Separation, [alpha] = 0.05. Table 2. Thatch depth and shoot density of bentgrass as affected by B rate and cultivar, June 2000 and 2001. Thatch depth June June Shoot density 2000 2001 June 2001 shoots mm [cm.sup.2] B rate, kg [ha.sup.-1] [yr.sup.-1] 0.0 32.6 41.1 6.3 0.5 33.2 41.3 6.3 1.0 32.5 41.4 na ([dagger]) 2.0 32.8 41.3 6.2 Linear ([double ns ns ns dagger]) Quadratic ns ns ns Cultivar Penn A-2 34.6ab ([section]) 43.6a 7.0a Penn G-1 35.6a 44.3a 6.8ab Penn G-6 36.3a 44.1a 7.0a L-93 32.2cd 40.8b 5.7d SR-1020 31.0d 39.2bc 6.4bc Dominant 33.4bc 41.1b 6.1cd Crenshaw 32.5cd 41.3b 6.0cd Penn G-2 30.6d 38.1c 6.3c Penncross 28.5e 38.5c 5.1e ([dagger]) na, not available. ([double dagger]) Significance of regression equations fit to the data; ns, not significant. ([section]) Within each sampling date, means separation by Duncan's Mean Separation, [alpha] = 0.05. Table 3. Boron concentration and uptake by bentgrass cultivars as affected by B rate, June 2000 and 2001. June 2000 B uptake Concentration g [m.sup.-2] ug [g.sup.-1] B Rate, kg [ha.sup.-1] 0.0 0.04 4.8 0.5 0.04 4.9 1.0 0.04 5.1 2.0 0.04 5.0 Linear ([dagger]) ns ns Quadratic ns 0.007 Cultivar Penn A-2 0.03b ([double dagger]) 5.2a Penn G-1 0.03b 5.2a Penn G-6 0.04b 4.8a L-93 0.04b 4.7a SR-1020 0.04b 4.7a Dominant 0.03b 4.9a Crenshaw 0.03b 4.8a Penn G-2 0.04b 5.Oa Penncross 0.07a 5.3a June 2001 B uptake Concentration g [m.sup.-2] ug [g.sup.-1] B Rate, kg [ha.sup.-1] 0.0 0.05 8.7 0.5 0.06 9.5 1.0 0.05 10.0 2.0 0.06 9.9 Linear ([dagger]) ns ns Quadratic ns ns Cultivar Penn A-2 0.04c 9.1a Penn G-1 0.04c 9.8a Penn G-6 0.04c 10.0a L-93 0.04c 10.0a SR-1020 0.05bc 9.0a Dominant 0.07b 9.2a Crenshaw 0.04c 9.4a Penn G-2 0.07b 9.4a Penncross 0.10a 9.8a ([dagger]) Significance of regression equations fit to the data; as, not significant. ([double dagger]) Within each sampling date, means separation by Duncan's Mean Separation, [alpha] = 0.115.
Adams, J.F., C.C. Mitchell, and H.H. Bryant. 1994. Soil test fertilizer recommendations for Alabama crops. Agron. and Soils Dep. Series No. 178. Alabama Agric. Exp. Stn., Auburn Univ.
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E. A. Guertal *
Dep. of Agronomy and Soils, 253 Funchess Hall, Auburn Univ., AL 36849. Received 6 Feb. 2003. * Corresponding author (firstname.lastname@example.org).
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|Title Annotation:||Turfgrass Science|
|Date:||Jan 1, 2004|
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