Irrigation and Nitrogen and Potassium Effects for Two Turfgrass Species and a Common Lawn Mixture

Research Article
Sang-Kook Lee1*Kevin W. Frank2

Abstract

Water requirements for turfgrass have been estimated on water use rates, and irrigation frequency and quantity. However, these parameters do not always provide adequate guidance for the efficient irrigation management. Research was conducted for 2005 and 2006 to determine recommendations for irrigation and nitrogen and potassium program for two turfgrass species and a common lawn mixture. The irrigation treatments were precipitation only, 0.5 cm of water every other day, and 1.8 cm of water once per week. The nitrogen (N) treatments were 98, 156, and 208 kg N ha-1 yr-1. The low, medium, and high N treatments were applied over 2, 4, and 6 applications, respectively. No phosphorus (P) was applied as a soil test indicated a high soil P level. Treatments were evaluated on Kentucky bluegrass, tall fescue, and the lawn mixture of Kentucky bluegrass, perennial ryegrass, creeping red fescue, and Chewings fescue. Research indicated that all turfgrass species without irrigation had turfgrass quality lower than the acceptable turfgrass quality rating of six during a portion of the growing season and significant differences were found among irrigation treatments. However, the precipitation only treatment had acceptable quality ratings on 8 of 12 sampling dates for two years. If water resource is limited, and turfgrass quality for low maintenance in July and August are not important, the precipitation only treatment would be accepted under the environmental conditions which occurred in regions similar to the area where the research was conducted.

Keyword



Introduction

Appropriate water management is critical to maintain turfgrass quality especially during the summer months. Common irrigation recommendations for turfgrass are to irrigate deep and infrequently in order to achieve a deep root system that will be better suited to endure prolonged drought conditions and maximize drought resistance (Qian and Fry, 1996a). Fry and Huang (2004) defined deep and infrequent irrigation as irrigation to furnish water for root zone when the first signs of leaf wilt appear. In general, deep and infrequent irrigation refers to applying large amounts of irrigation, 1.3 to 2.5 cm or more, in a single irrigation event. A number of research projects have been reported to support benefits of deep and infrequent irrigation. Bennett and Doss (1960) reported infrequent irrigation promoted better root development for both cool- and warm-season grasses. Madison and Horgan (1962) found better root growth with infrequent irrigation for warm-season grasses. Deeply and infrequently irrigated bentgrass produced higher levels of water soluble carbohydrate (Fu and Dernoeden, 2008). Jordan et al. (2003) investigated the responses of creeping bentgrass intensively managed to irrigation frequency of every four days and every day or every other day. They found creeping bentgrass with a frequency of every four days irrigation had greater turfgrass quality, shoot density, and root length than the other two irrigation frequencies. Johnson (2003) studied to compare irrigations with 2-, 4-, and 6-day interval for the response of Kentucky bluegrass (Poa pratensis), tall fescue (Festuca arundinacea), prairie junegrass (Koeleria macrantha), and buffalograss (Buchloe dactyloides). He reported that irrigation of 2-day interval produced greater turfgrass quality than irrigation of 4- or 6-day interval.

However, deep and infrequent irrigation is not recommended for all turfgrass situations. Turfgrass grown on sandy soils should be irrigated with smaller amounts of water more frequently as deep infrequent irrigations could potentially result in losses of irrigation water through leaching. Also, turfgrass grown on fine textured soils with low infiltration rates should be irrigated with smaller amounts of water more frequently to avoid run-off and puddling on the surface. The alternative to deep and infrequent irrigation is light and frequent irrigation. Light and frequent irrigation would be defined as maintaining soil at field capacity to apply irrigation when the first sign of leaf wilt is shown (Fry and Huang, 2004). Light and frequent irrigation is commonly used with small amounts of water, 0.3 to 0.6 cm, every day or every other day.

Common perceptions of light and frequent irrigations are that they promote shallow rooting in turfgrass thereby making the turf more susceptible to dry soil conditions. Furthermore, frequent irrigation applications are often implicated in increased weed interference. Despite all the negative effects put forth for light frequent irrigation applications there are some positive effects reported. Melvin (1991) investigated effects of frequent and infrequent irrigation to turfgrass rooting depth and thatch thickness of Kentucky bluegrass. He found no differences between frequent and infrequent irrigation for rooting depth of Kentucky bluegrass, although Smiley et al. (1980) reported that frequent irrigation results in shorter rooting depth of Kentucky bluegrass sod. Melvin also reported that daily irrigation treatments have also been shown to have a smaller thatch layer than weekly irrigation treatments. Research by Melvin and Vargas (1994) revealed that light and frequent irrigation treatments, 0.3 cm every day at 12 p.m., reduced the symptoms associated with necrotic ring spot (Leptosphaeria korrae). Jiang et al. (1998) also found that a light daily irrigation resulted in higher turfgrass quality, and reduced brown patch incidence when compared to deep infrequent irrigation based upon returning 80% of evapotranspiration weekly. Karnok and Tucker (1999) found that light and frequent irrigation decreased the symptoms of localized dry spot on creeping bentgrass (Agrostis stolonifera)). Starrett et al. (1996) concluded that light and frequent irrigation had less pesticide leaching than deep and infrequent irrigation.

Although common irrigation recommendation for turfgrass is deep and infrequent irrigation, the recommendation is not proper for all turfgrass management. The objective of this study was to determine irrigation and nutrient recommendation for three cool-season turfgrass species.

Materials and Methods

In spring 2005, research was initiated at the Hancock Turfgrass Research Center on the campus of Michigan State University in East Lansing, Michigan. Each plot size for the study was 3.7 by 3.7 m. Irrigation and fertility treatments were initiated on Kentucky bluegrass (Poa pratensis), tall fescue (Festuca arundinacea), and a mixture of 40% Kentucky bluegrass, 25% creeping red fescue (Festuca rubra L.), 20% perennial ryegrass (Lolium perenne), and 15% Chewings fescue (Festuca rubra subsp. commutata) on 25 April 2005. The three irrigation treatments were none (precipitation only), 0.5 cm applied every other day, and 1.8 cm applied once a week at one irrigation event. All irrigation treatments were applied at 6:00 a.m. The treatment list and application timing are listed in Table 1. The nitrogen (N) treatments were 98, 156, and 208 kg N ha-1 yr-1 for the low, medium, and high N rate treatments, respectively. The low, medium, and high N treatments were applied over 2, 4, and 6 applications, respectively. Nitrogen was applied using a mixture of sulfur coated urea (SCU) and urea at a ratio of 25% SCU to 75% urea. The potassium (K) applied from muriate of potash (0-0-60) at a ratio of 2:1 (N:K) for all treatments was applied. There was no phosphorus treatment for the study. All fertilizer was granular type and applied using a drop fertilizer spreader (Gandy 24H13, Gandy Company). Immediately following each fertilizer application, 1.3 cm of irrigation was applied.

Table 1. Treatment list and application plan. http://dam.zipot.com:8080/sites/WTS/images/N0260100208_image/Table_WTS_10_02_08_T1.png

yApplication schedule for 2006. In 2005, the first treatment was applied 25 April.

zLawn mix is a turfgrass mixture of Kentucky bluegrass, perennial ryegrass, creeping red fescue, and Chewings fescue.

The turfgrass was mowed weekly and clippings returned to the plots. Turfgrass color was measured by visual evaluation every two weeks from 2005 through 2006 using a scale of 1 to 9 (1=straw brown, 6=acceptable, and 9=dark green). Turfgrass quality ratings were measured by visual evaluation from 2005 and 2006 using a scale of 1 to 9. (1=poor, 6=acceptable, and 9=best). Turfgrass clippings were collected every two weeks from a 3.8 m2 area of each plot, dried at 67℃ for 48 hours, weighed and analyzed for nitrogen, phosphorus, and potassium using Dumas method (AOAC 968.06). Soil samples were taken every month at the depth of 0 to 10 cm and analyzed for nitrate nitrogen, ammonium nitrogen, phosphorus and potassium levels. A cadmium reduction method was used to analyze nitrate nitrogen (Huffman and Barbarick, 1981) and the Salicylate Method was used for ammonium nitrogen (Nelson, 1983). The extractant of 1M NH4OAc was used for soil K analysis (Warncke and Brown, 1998). Volumetric water content (%) in the soil was measured at the depth of 12 cm every two weeks by Time Domain Reflectometry (Field Scout TDR-300, Spectrum Technologies, Aurora, USA).

The experimental design was a randomized complete-block design with a split-plot arrangement and three replications. The irrigation, species, and N rate treatments were arranged in a 3k factorial. Analysis of variance (ANOVA) was performed on transformed data using Statistical Analysis Systems design with k=3 (Montgomery, 1985). The following factors were used in the study.

1. Three irrigation treatments were precipitation only, 0.5 cm application every other day, and 1.8 cm application once a week.

2. Turfgrass types were Kentucky bluegrass, tall fescue, and a lawn mix.

3. Fertilizer rates were 98, 156, and 208 kg N ha-1 yr-1 for the low, medium, and high nitrogen (N) rate treatments.

PROC MIXED was used for multiple factor analyses of variance (SAS Institute Inc., 2001). Fisher’s least significant difference (LSD) was used for mean separation, when effects were significant at P≤0.05.

Results and Discussion

Turfgrass quality

There was an irrigation main effect on four of 12 rating dates (Table 2). In 2005, the weekly and every other day irrigation treatments had the highest turfgrass quality ratings for August and September. There were no significant differences between the weekly and every other day irrigation treatments on turfgrass quality throughout the research. For the precipitation only treatment, the turfgrass quality ratings in August and September were less than six. In 2006, all irrigation treatments had turfgrass quality greater than six with the exception of the precipitation only treatment for July and August. The precipitation only treatment had acceptable quality ratings on eight of 12 rating dates during the research. If water resource is limited, and turfgrass quality for low maintenance in July and August are not important, the precipitation only treatment would be accepted for the area where the research was conducted. Richie et al. (2002) investigated the response of tall fescue to irrigation scheduling. They found plots irrigated with two irrigation events per week produced greater turfgrass quality than plots irrigated with three irrigation events per week. Johnson (2003) found that a two day irrigation interval produced greater turfgrass quality than four and six day irrigation intervals. Fry and Butler (1989) found similar results, tall fescue maintained high turfgrass quality by watering at 50 percent of estimated ETp every other day during summer months in Colorado, but weekly irrigation at this same level resulted in unacceptable turfgrass quality. However, we found no differences for turfgrass quality between every other day and weekly irrigation events. Qian and Fry (1996b) concluded there were no differences on turfgrass quality between daily and infrequent irrigation at the first sign of leaf roll since the last irrigation.

Table 2. Mean turfgrass quality for irrigation main effect. http://dam.zipot.com:8080/sites/WTS/images/N0260100208_image/Table_WTS_10_02_08_T2.png

yTufgrass quality was rated from 1 to 9 (1=worst, 9=excellent, and 6=acceptable).

zMeans in a column within a year followed by the same letter are not significantly different according to Fisher’s least significant difference (LSD) (P=0.05).

There was a significant turfgrass species main effect on 10 of 12 rating dates (Table 3). Tall fescue had the highest or equal to the highest turfgrass quality ratings except for September and October 2006. The lawn mixture had the lowest or equal to the lowest turfgrass quality rating throughout the research. The water balance for August 2005 and July 2006 was low because of low precipitation (Fig. 1). The ETp rate for August 2005 and July 2006 was 11.0 and 15.0 cm, respectively (data not shown). The water balance for August 2005 and July 2006 was -0.2 and 1.1 cm with irrigation, respectively. Without irrigation, the water balance for August 2005 and July 2006 were -7.7 and -6.4 cm, respectively. However, tall fescue had the highest quality for July 2006. The response of tall fescue to water deficit may result from deep rooting system of tall fescue that can reach water sources deeper in the soil profile (Qian et al., 1997). When performance of hybrid bluegrasses was compared with tall fescue and Kentucky bluegrass, tall fescue had the highest turfgrass quality without irrigation (Bremer et al., 2006). In the current research, there was a significant difference between tall fescue and Kentucky bluegrass on seven of 12 rating dates. Among these rating dates, tall fescue had greater turfgrass quality than Kentucky bluegrass on five of the seven rating dates. The lawn mixture had turfgrass quality less than six on five of 12 rating dates while tall fescue and Kentucky bluegrass had turfgrass quality ratings less than six on only one and two of 12 rating dates, respectively. Based on these results, regardless of irrigation treatments, tall fescue would be a better selection than lawn mixture to maintain high quality turfgrass.

Table 3. Mean turfgrass quality for species main effect. http://dam.zipot.com:8080/sites/WTS/images/N0260100208_image/Table_WTS_10_02_08_T3.png

xLawn mixture is a combination of Kentucky bluegrass, perennial ryegrass, creeping red fescue, and Chewings fescue.

y Tufgrass quality was rated from 1 to 9 (1=worst, 9=excellent, and 6=acceptable).

z Means in a column within a year followed by the same letter are not significantly different according to Fisher’s least significant difference (LSD) (P=0.05).

There was a significant N rate main effect for turfgrass quality (Table 4). The medium N rate treatment had the highest or equal to the highest turfgrass quality rating on four of 12 rating dates. While the medium N rate treatment had the highest turfgrass quality on three rating dates during 2005, it had the highest turfgrass quality on only one date in 2006. The high N rate treatment had the highest turfgrass quality rating on four of 12 rating dates throughout the research. There were significant differences between the medium and high N rate on seven of 12 rating dates. The high N rate treatment had the highest turfgrass quality on July and August for both 2005 and 2006. The low N rate treatment had turfgrass quality less than six on four of 12 rating dates throughout the research. The medium and high N rate treatment produced turfgrass quality less than six on two and one of 12 rating dates for both 2005 and 2006, respectively. All N rate treatments had turfgrass quality ratings less than six on September 2005. Turfgrass quality for September 2005 was rated on 6 September 2005. Turfgrass quality for September 2005 should be affected from treatments and weather condition of the previous month. According to the application plan, there was no N application on August. In the case of low N rate treatment, there was a four month interval between applications because of two applications a year. In the case of the medium and high N rate treatments, there were three and two month intervals between applications because of four and six treatments per year, respectively. Acceptable turfgrass quality would not be expected with two to four month interval for N application. In addition to no N application on August, the water balance was the lowest in August 2005 in both 2005 and 2006. Cool-season turfgrass during growing season under well-watered condition generally required average water use rate of 0.8 to 2.5 cm per day (Huang and Fry, 1999). However, the water balance calculated by precipitation and ETp was -0.2 cm per month with irrigation treatments and -7.7 cm per month without irrigation treatments in August 2005 (Fig. 1). Additional irrigation is required for proper turfgrass growth under the condition. In September 2006, there was no significant difference among N rate treatments for turfgrass quality and all treatment had turfgrass quality greater than six because of an unscheduled fertilizer application of 49 kg N ha-1 to the entire plot area two weeks prior to ratings. Water balance was 7.1 cm per month with irrigation treatment and -0.4 cm per month without irrigation treatment for August 2006. Water balance was relatively higher in August 2006 than in August 2005. Based on the result of this study, the medium and high N rate would be recommended for higher turfgrass quality although there was turfgrass quality below acceptable rating of six with the medium and high N rate treatment.

Table 4. Mean turfgrass quality for nitrogen rate main effect. http://dam.zipot.com:8080/sites/WTS/images/N0260100208_image/Table_WTS_10_02_08_T4.png

xN rate units are kg ha-1 yr-1.

y Turfgrass quality was rated from 1 to 9 (1=worst, 9=excellent, and 6=acceptable).

z Means in a column within a year followed by the same letter are not significantly different according to Fisher’s least significant difference (LSD) (P=0.05).

http://dam.zipot.com:8080/sites/WTS/images/N0260100208_image/Fig_WTS_10_02_08_F1.png

Fig. 1. The amount of water received from precipitation and irrigation treatment. Evaportranspiration rate was included to caculate water balance. Irrigation treatment means either weekly and every other day treatments. The plots with weekly and every other day irrigation treatment received the same amount of water over time, only the application timing interval varied. Water balance was calculated from precipitaton, irrigation, and ETp (Water balance=precipitation+irrigation–ETp).

Turfgrass clipping yields

There was a significant irrigation by species interaction for the August 2005, July, August, and October 2006 rating dates (Fig. 2). The precipitation only treatment had the lowest or equal to the lowest clipping yield for all species for these sampling dates except for October 2006. In August 2005, every other day irrigation treatment had higher clipping yields than the weekly irrigation treatment among all species. Qian and Fry (1996b) reported clipping yield of zoysiagrass with daily irrigation was 30% higher than clipping yield with infrequent irrigation. However, there was no difference between every other day and weekly irrigation treatment for clipping yield in August 2006 for the study. The precipitation amount in August 2006 was 12.2 cm while the plots received 3.3 cm of precipitation in August 2005. Every other day irrigation treatment had more effect on clipping yield than the weekly irrigation treatment under the weather condition of low precipitation level. With both every other day and weekly irrigation treatment, the lawn mixture had the highest clipping yields in August 2005. The lawn mixture had the highest or equal to the highest clipping yields with weekly irrigation treatment when irrigation by species interactions were found. There were no differences among species for clipping yields for the precipitation only treatment except for October 2006.

There was a significant species by N rate interaction on three of 12 sampling dates. Tall fescue had the highest or equal to the highest clipping yield at any N rate for June 2005 and August 2006 (Fig. 3). Kentucky bluegrass had the lowest clipping yield at any N rate in June 2005 and the lowest or equal to the lowest clipping yield in October 2005 and August 2006. Overall, clipping yield was increased with N rate increase from the low to medium N rate.

http://dam.zipot.com:8080/sites/WTS/images/N0260100208_image/Fig_WTS_10_02_08_F2.png

Fig. 2. Irrigation×species interaction for clipping yield (g m-2) for 2005 and 2006. Mean with the same upper case letters is not significantly different among irrigation treatments by Fisher’s least significant difference (LSD) test (P=0.05). Mean with the same lower case letters is not significantly different among species by Fisher’s LSD test (P=0.05).

http://dam.zipot.com:8080/sites/WTS/images/N0260100208_image/Fig_WTS_10_02_08_F3.png

Fig. 3. N rate×species interaction for clipping yield (g m-2) for 2005 and 2006. Mean with the same upper case letters is not significant among N rate treatments by Fisher’s least significant difference (LSD) test (P <0.05). Mean with the same lower case letters is not significant among species by Fisher’s LSD test (P <0.05).

There was a significant irrigation by N rate interaction on five of 11 sampling dates for turfgrass clipping yield. The precipitation only treatment had the lowest or equal to the lowest clipping yield at any N rate except for September 2005 and 2006 (Fig. 4). The high N rate had the highest or equal to the highest amount of clipping yield at any irrigation treatment. Overall, clipping yields was increased with irrigation treatment and increase of N rate.

http://dam.zipot.com:8080/sites/WTS/images/N0260100208_image/Fig_WTS_10_02_08_F4.png

Fig. 4. Irrigation×N rate interaction for clipping yield (g m-2) for 2005 and 2006. Mean with the same upper case letters is not significantly different among irrigation treatments according to Fisher’s least significant difference (LSD) test (P=0.05). Mean with the same lower case letters is not significantly different among N rate treatments according to Fisher’s LSD test (P=0.05).

There was an irrigation main effect for clipping yield on five of 11 sampling dates (Table 5). The precipitation only treatment had the lowest or equal to the lowest clipping yield for all sampling dates when significant differences were found among irrigation treatments. Every other day and weekly irrigation treatments had the highest clipping yield on five and four of 11 sampling dates, respectively. There was only one sampling date when there was significant difference between every other day and weekly irrigation treatments, August 2005. Every other day irrigation treatment had about 43% more clipping yield than the weekly irrigation treatment in August 2005 which had the lowest water balance. Every other day irrigation was more effective for shoot growth than weekly irrigation when ETp replacement is insufficient to equal transpiration rate. According to Qian and Fry (1996b), infrequent irrigation promotes faster shoot growth of turfgrass. They reported shoot growth of infrequently watered turfgrass was 24% more than that of frequently watered turfgrass. There was no significant difference for total clipping yield in 2005. Every other day and weekly irrigation events had the highest total clipping yield in 2006. This result was probably due to an unscheduled fertilizer application of 49 kg N ha-1 to the entire plot area two weeks prior to ratings in August 2005.

There was a significant species main effect for clipping yield on all sampling dates (Table 6). The lawn mixture had the highest or equal to the highest clipping yield for all sampling dates. The highest total clipping yield was from the lawn mixture for two years. The lawn mixture had 110 and 26% more total clipping yield than Kentucky bluegrass in 2005 and 2006, respectively. The lawn mixture had 21 and 30% more total clipping yield than tall fescue in 2005 and 2006, respectively. The lawn mixture had a turfgrass quality rating of six on five of 12 rating dates while tall fescue and Kentucky bluegrass had turfgrass quality rating less than six on one and two of 12 sampling dates, respectively. The lawn mixture produced the lowest turf quality with the highest clipping yield which is undesirables for turfgrass management. Therefore, tall fescue or Kentucky bluegrass would be better selection than lawn mixture to promote turfgrass quality and reduce clipping yield.

Table 5. Mean turfgrass clipping yield for irrigation main effect. http://dam.zipot.com:8080/sites/WTS/images/N0260100208_image/Table_WTS_10_02_08_T5.png

xClipping yield units are g m-2.

y Means in a column within a year followed by the same letter are not significantly different according to Fisher’s least significant difference (LSD) (P =0.05).

z No data available.

Table 6. Mean turfgrass clipping yield for irrigation main effect. http://dam.zipot.com:8080/sites/WTS/images/N0260100208_image/Table_WTS_10_02_08_T6.png

wLawn mixture is a combination of Kentucky bluegrass, perennial ryegrass, creeping red fescue, and Chewings fescue.

x Clipping yield units are g m-2.

y Means in a column within a year followed by the same letter are not significantly different according to Fisher’s least significant difference (LSD) (P =0.05).

z No data available.

There was a significant N rate main effect on 10 of 11 sampling dates (Table 7). The low N rate treatment had the highest or equal to the highest clipping yield on May and September 2005. These results were due to amount of applied per application because the single application of the low N rate treatment had the largest amount of N. However, the result in 2006 is different because of an unscheduled fertilizer application of 49 kg N ha-1 to the entire plot area two weeks prior to ratings. The low N rate treatment had the lowest clipping yield on August 2005 and 2006. The low N rate treatment had two applications per year with a four month interval between applications. The N source is 75% urea and 25% SCU which would not be expected to last four months. Therefore, the lowest clipping yield with the low N rate treatment would be expected.

Both the medium and high N rate treatment had the highest or equal to the highest clipping yield on five of 11 sampling dates, respectively. There were significant differences between the medium and high N rate treatments except the sampling date on August 2005 when significant differences were found among N rate treatments. While no significant difference was found on August 2005, there was a difference in August 2006. Water balance in August 2005 was -0.2 cm compared to 7.1 cm in August 2006. The medium N rate treatment had the highest amount of total clipping yield in 2005 while the high N rate treatment had the highest total clipping yield in 2006. When weather condition is dry, there was no significant difference between the medium and high N rate treatments. Researches have shown that clipping yield is increased with N application (Kopp and Guillard, 2002; Starr and Deroo, 1981; Teutsch et al., 2005). When clippings are returned, additional N contained in clippings will be added. Heckman et al. (2000) returned Kentucky bluegrass clippings to turf using a mulching mower. They found turfgrass clippings improved the color and quality compared to removing clippings and reducing N rate by 50% did not affect turfgrass color when clippings were returned. Although both the medium and high N rate treatment produced the highest amount of total clipping yield on most sampling dates, the medium N rate would be recommended to maintain turfgrass quality with lower clipping yield.

Table 7. Mean clipping yield for nitrogen rate main effect. http://dam.zipot.com:8080/sites/WTS/images/N0260100208_image/Table_WTS_10_02_08_T7.png

wN rate units are kg ha-1 yr-1.

x Clipping yield units are g m-2.

y Means in a column within a year followed by the same letter are not significantly different according to Fisher’s least significant difference (LSD) (P <0.05).

z No data available.

Soil moisture content

In 2005, every other day irrigation treatment had the highest or equal to the highest soil moisture content throughout the research (Table 8). There were significant differences between the weekly and every other day irrigation treatments for the July 2005 rating. Despite the difference in soil moisture content in July 2005, there were no differences in turfgrass color and quality between the irrigation treatments in July 2005. These results of turfgrass color and quality was probably due to relatively high precipitation rate of 14.3 cm in July 2005 (data not shown). It is two times greater amount of water than that of water from irrigation treatment and the greatest amount of precipitation for the year. This amount of precipitation in July 2005 was sufficient for acceptable color and quality rating. The precipitation only treatment had the lowest soil moisture content during 2005. Water balance was -0.2 cm in August 2005 due to the 11 cm ETp and low precipitation (Fig. 1). Under the weather condition, turfgrass can be stressed and result in limiting growth without additional irrigation when ETp replacement is insufficient to equal transpiration rate. In the result of this study, turfgrass quality treated by precipitation only in August and following September 2005 was less than acceptable turfgrass quality of six.

In 2006, every other day irrigation treatment had the highest or equal to the highest soil moisture content. The precipitation only treatment had the lowest soil moisture content for the year. With the lowest soil moisture content, the precipitation only treatment had the lowest turfgrass quality and ratings lower than six in July and August. There were no differences between every other day and weekly irrigation treatment for turfgrass quality in July and August which had the weather condition of 15.0 and 12.6 cm ETp, respectively. Water balance in July and August was 1.1 and 7.0 cm, respectively. Under this condition, soil moisture content of 22.1% was insufficient level to generate acceptable turfgrass quality without irrigation treatments. Acceptable turfgrass quality was not produced without irrigation treatment. Watson (1950) investigated the response of turfgrass consisting of mixed bentgrass, red fescue, and Kentucky bluegrass to four levels of soil moisture content and five soil compaction levels. He reported the average soil moisture content for the growing season is about 16 to 18%. Although soil moisture content was higher than 18% in August, acceptable turfgrass quality was not produced. It may result from relatively high ETp of 12.6 cm and high mean temperature of 27.3℃.

Table 8. Mean soil moisture content for irrigation main effect. http://dam.zipot.com:8080/sites/WTS/images/N0260100208_image/Table_WTS_10_02_08_T8.png

x No data available.

y Soil moisture content units are percent.

z Means in a column within a year followed by the same letter are not significantly different according to Fisher’s least significant difference (LSD) (P =0.05).

We found that different timing of irrigation applications had effects on clipping yield and soil moisture content. However, there were no differences on turfgrass color and quality between every other day and the weekly irrigation treatments. Both every other day and weekly irrigation treatments had turfgrass quality greater than acceptable quality of six throughout the study. Precipitation only treatment had turfgrass quality less than six on four of 12 rating dates. Most of these ratings occurred during the summer months from July to September with dry weather conditions. If water resource is limited, and turfgrass quality for low maintenance from July to September are not important, precipitation only treatment would be accepted under the weather conditions of the research area. If maintaining turfgrass quality in summer months is important for the turfgrass manager, then either every other day or the weekly irrigation treatment would be acceptable.

Although the lawn mix had the greatest shoot growth for most sampling dates, tall fescue had the highest turfgrass quality on eight of 12 rating dates. The highest soil moisture content was also found in the tall fescue plots. Tall fescue maintained acceptable turfgrass quality for two years except one rating date while the lawn mixture had turfgrass quality less than six on five rating dates for two years. Compared to tall fescue, Kentucky bluegrass had turfgrass quality greater than six on five rating dates for the study. Based on the results of the study, tall fescue would be recommended to maintain turfgrass quality, soil moisture content, and less clipping yield. Although Kentucky bluegrass had less turfgrass quality than tall fescue during spring and summer months, Kentucky bluegrass was still acceptable to maintain acceptable turfgrass quality for home lawn area.

There were significance differences between the medium and high N rate treatments for turfgrass quality. Although both the medium and high N rate treatments maintained acceptable turfgrass quality throughout the study except for two and one rating date, respectively, the high N rate treatment had greater turfgrass quality than the medium N treatment for July and August in both 2005 and 2006. The medium N rate treatment had turfgrass quality less than six on September 2005 and August 2006. During the summer months, the high N rate produced better turfgrass quality than the medium N rate treatment. Overall, the medium N rate treatment would be accepted for acceptable turfgrass quality. If high maintenance turfgrass quality is required, then the high N rate is needed to maintain high turfgrass quality.

Acknowledgement

Financial support for the study was provided by Project GREEEN, Lesco and the Michigan Turfgrass Foundation. Special thanks to Ben Hamza, Ken Tornberg, and Paul Ferrell for protocol development.

Authors Information

Sang-Kook Lee, Hoseo University, Associate Professor

Kevin W. Frank, Michigan State University, Professor

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