Sun Xiao-yang, Wang Peng, Xie Fu-chun, Sun Hua-shan, Guan Tong, Zuo Yang, Li Hong, and Chen Ya-jun

College of Horticulture, Northeast Agricultural University, Harbin 150030, China

Abstract: The mowing height and mowing frequency are the key factors that affect the turf quality and turfgrass growing ability. The purpose of this study was to reveal the alternative efficient interaction between mowing height and mowing frequency in Kentucky bluegrass turf management. The Kentucky bluegrass cultivar 'Kenblue' (Poa pratensis L.) was used to evaluate the interactions of mowing heights (H1, H4 and H7) and mowing frequencies (F2, F5 and F8) on the performance of turfgrass and turf physiological responses under the field condition. The results showed that the treatment of H7×F8 had perfect influence on the turf texture, root elongation, and also enhanced soluble sugar and free proline content in plants. While, the turf quality, color, uniformity and the increasing tiller numbers were performed more superior in the treatment of H4×F5 than other treatments. In all the interacting treatments, the relation between leaf green index and number of shoots (dm2) was positively correlated, thus, it could be speculated that the proper mowing height with frequency had a strong impact on the increasing of turfgrass tillers. On the whole, the interaction of H4×F5 on turf quality was the most excellent treatment in this experiment.

Key words: Kentucky bluegrass, turf, mowing, height, frequency

Introduction

Mowing is the main cultural practice for all the turfgrass in that it influences most other cultural operations in turfgrass management. It relates to the periodic removal of a portion turfgrass shoot growth.Mowing may be performed to maintain top growth within specific limits, control undesired vegetation that is in tolerant of mowing, sustain an ornamental or recreational turf, produce a true putting surface, or develop a sod crop (Turgeon, 2008). Mowing height refers to the height of the turfgrass left on the ground after mowing. Mowing height mainly depends on its purpose and functions, and also turf maintenance capabilities. Mowing frequency refers to the turf mowing times within a certain period. Mowing frequency mainly depends on mowing height and growth rate (Yu, 2009). With the decreasing frequency of mowing and the increase of stubble height, the density of turf grass decreases, the width of leaves increases and the texture becomes worse (Wang et al., 2014). Mowing can improve leaf chlorophyll content and promote root activity of turf grass, the best mowing frequency of Bermuda grass (Cynodon spp.)is once a fortnight. Frequently, mowing can increase the shoot density of turfgrass, promote the tillering and inhibit growth (Zeng et al., 2015). The growth of turfgrass is decreased while the water consumption is increased with the mowing stubble height. Reducing the height of mowing stubble can significantly reduce the water consumption and increase turfgrass growth(Li et al., 2007). Mowing height in different seasons is different, in general, mowing height in summer is higher than that in winter (Yang et al., 1999). In this study, the combined effect of mowing height and frequency on the turf quality of Kentucky bluegrass(Poa pratensis L.) was studied based on Heilongjiang Province climatic conditions, and the superior mowing combination was selected to provide reference for the conservation and management of turfgrass in northern China.

Materials and Methods

Plant materials

A commercial Kentucky bluegrass (Poa pratensis L.)cultivar 'Kenblue' produced in the USA was introduced for this study. The cultivar 'Kenblue' belonged to the common type based on morphological traits of Kentucky bluegrass classification system (Josh et al., 2012).It had erect growth habit, narrow leaf blades, early flowering and high seed yields, making it the most cultivated for conservation purposes and lower maintenance utility turf in Heilongjiang Province, China.

Methods

The field plots were conducted as completely random block design at the horticultural experiment station of Northeast Agricultural University (E 126°30′,N 45°50′) from May 20 to October 20, 2017. Field climatic characteristics belonged to the temperate continental monsoon climate with long winter and short summer. The annual average precipitation was 569 mm.Black loam soil with the content of organic matter was 15.8 g · kg-1, and pH 7.0. In May 20, seeds were sown into the plots from which each plot area was 1 m2.Seedlings grown out after 1 week sowing and field routinely managed until mowing treatments began.

Different mowing heights and mowing frequencies were imposed at same time to the turfgrasses after 8 weeks normal cultural management. The mowing heights were set up to 1, 4 and 7 cm, which were denoted by H1, H4 and H7; while the mowing frequencies were designed to 2, 5 and 8 days, and they were indicated by F2, F5 and F8. The total nine interactive treatments with four replications are shown in Table 1. After 2 months treatment, samples were collected for measurements.

Table 1 Experimental design

Data analysis

Analysis of variance (ANOVA) and correlation of individual growth parameters was performed using SAS (Version 9.3, SAS Institute Inc.). Used Sigmaplot(Version12.0, Systat Software, Inc.) statistical software regression analysis between the leaf green index and each growth index. The regression equation was f=ax+b, where, a was the correlation coefficient.The variation and distribution of soluble sugar and proline in different treatments of mowing height and frequency were described by the bar graph.

Results

Effects of mowing height and frequency interaction on growth of Kentucky bluegrass

Table 2 showed that Kentucky bluegrass turf quality and number of shoots (dm2) were performed the best under the treatments of H4×F5 and H4×F2,respectively, and were significantly different from others (P＜0.05). Color and uniformity were excellent with the interactions of H4×F5 and H4×F8 treatments,which were significantly higher than those of other treatments (P＜0.05). Solube sugar and proline contents were distinguished higher in the treatment of H7×F8(P＜0.05). Under the treatments of H7×F8 and H7×F5,the root depth of Kentucky bluegrass was longer and more tillers in root system than others.

Table 2 Growth characteristics of Kentucky bluegrass under different mowing heights and mowing frequency treatments

Table 3 showed that under the single factor analysis of mowing height and frequency, the measurements of Kentucky bluegrass were different from under the interaction treatments. Except for the uniformity in the single factor of mowing frequency treatment (P=0.54), all other indexes either with single factor or with interaction factors were significant different (P＜0.05).

Table 3 Two-way ANOVA on each index of Kentucky bluegrass under different heights and frequency interaction treatments

Correlation analysis on growth indexes of Kentucky bluegrass in interactive manipulation mowing height and frequency.

Table 4 showed that turf quality, color, uniformity;color, leaf blade width, number of shoots (dm2);uniformity, number of shoots (dm2); leaf blade width,root length, soluble sugar, proline; sugar and proline were positively correlated with each other (P＜0.05).However, uniformity was negatively correlated with leaf blade width, root depth, soluble sugar and proline contents (P＜0.05).

As shown in Table 4, the correlation coefficients of soluble sugar and proline, leaf blade width and root depth, turf quality and number of shoots (dm2), turf quality and color were 0.960, 0.955, 0.951 and 0.729,respectively. The larger the correlation coefficient was,the greater the relevance of each index of Kentucky bluegrass under the interaction of mowing height and frequency was.

Table 4 Correlation analysis between each index of under different mowing heights and frequency interaction treatments

Effects of mowing height and frequency interaction on Kentucky bluegrass in soluble sugar and proline assignment

Fig.1a and b showed that under the same mowing height, soluble sugar and proline contents under different mowing frequencies had significant difference (P＜0.05). As the mowing height increased, the contents of soluble sugar and proline enhanced.

In F2 frequency, there was no significant difference in soluble sugar content under different mowing heights (Fig. 1c and d). In F5 frequency, there was no distinguish difference in the height of H1 and H4,but there was a significant difference between the two and H7 (P＜0.05). Under the treatment of F8, there was no difference in the height of mowing H4 and H7, but there was significant difference between the two and H1 (P＜0.05). However, proline had significant difference under different mowing frequencies(P＜0.05). As the mowing height increased, the contents of soluble sugar and proline also increased.

Correlation between green index and growth index of Kentucky bluegrass under reciprocal mowing height and frequency

Table 5 showed the corresponding linear equations,and the correlation between green index and turf quality, color, uniformity, leaf blade width, root length, number of shoot (dm2), soluble sugar and proline.

The green index had some certain correlation with turf quality, color, uniformity, leaf blade width, root length, number of shoot (dm2), soluble sugar and proline. In the regression equation of f=ax+b, the greater the value of a, the greater the influence of leaf green index on each index. If a was a positive number,the leaf green index and the corresponding index were positive correlation. If a was negative, the leaf green index and the corresponding index were negatively correlated. Among them, the green index and number of shoots (dm2) and soluble sugar content were the most significant correlation.

Fig. 1 Effect of mowing height and frequency interaction treatments on soluble sugar and proline of Kentucky bluegrass

Table 5 Linear regression of mowing height and frequency on leaf green color with each index of Kentucky bluegrass

Discussion

Variation of growth index of Kentucky bluegrass under mowing height and frequency interaction

Turf quality can reflect the turfgrass growing situation.Generally, turf quality is divided into three groups including ornamental quality, functioning quality and ecological quality. This paper mainly researched on turf ornamental quality. Some standard measurements were used to evaluate turf quality, color, leaf blade width and uniformity (Li, 2013). Meanwhile, root length and number of shoots (dm2) also represented the turfgrass performance. Increasing the mowing frequency was more beneficial to the tillering of turfgrass and the increasing of root density effectively(Dai et al., 2015). Under the interaction of H4×F5, turf quality, color, leaf blade width and uniformity were the most significant well, which indicated that the turf ornamentation was more excellent under this treatment.Under H7×F8 interaction treatment, not only turfgrass with the longest root system growing, but also root tiller was the most vigorous, which indicated that this treatment was beneficial to turf establishment.

Effects of mowing height and mowing frequency interaction on soluble sugar and free proline in cells of Kentucky bluegrass

Soluble sugar and free proline were important components of osmotic solutes in the adaptive regulation of plants to abiotic stress (Zhao et al.,2010). Under the stress of adversity, large quantities of free proline and soluble sugar would accumulate in plant cells, and their accumulations were related to the resistance ability of plants (Xiao et al., 2005).Actually, mowing process stressed the turfgrass to tolerant the cutting damage. The changes of osmotic solutes could ameliorate and improve the turfgrass ability to adapt mowing stress. The experimental results showed that the mowing frequency and mowing height could induce the changes of soluble sugar and free proline contents, and soluble sugar and free proline were extremely positive correlation with the correlation coefficient 0.96. However, different mowing height treatments appeared no significant differences in the changes of soluble sugar, but the mowing frequency treatments had higher mowing frequency significantly reduced the contents of soluble sugar and free proline, which meant mowing height as a single factor had less effects on cells osmotic adjustment during the mowing process. The highest content of free proline was found in the treatment H7×F8, meanwhile, the external ornamental phenotype of turfgrass was relatively poor. These results indicated that the physiological indexes, such as free proline and sugar contents could be as indicators for selecting a suitable turf mowing pattern for practice.

Conclusions

In the process of the conservation and management of Kentucky bluegrass turf field, mowing technique was particularly important for grass visual quality.Proper mowing height with mowing frequency could effectively extend the turf green period, early greening period and promote vigorous growth of turfgrass.Leaf green index and number of shoots (dm2) were positively correlated in all the interacting treatments.The results of the present study indicated that the turf quality, color, uniformity and the increasing tiller numbers were performed the greatest in the treatment of H4×F5. Besides, although the treatment H4×F8 was less perfect than H4×F5, it also displayed good turf quality with lower mowing frequency that would be a better mowing pattern for economic use. Overall,the mowing treatment of H4×F5 was more fit for meticulous turf management of Kentucky bluegrass,while the treatment H4×F8 could be recommended for economic use, because it could save manpower in practical.