Effects Of Controlled-Release Fertilizers On Turfgrass Growth And Their Nutrient Leaching Characteristics

In recent years, controlled-release fertilizers (CRFs) have been widely used in lawn production as lawn industry is gaining its polularity. CRF can release nutrients slowly to suit plant nutrient uptake requirements during entire turfgrass growth period. This is not only beneficial to above ground and root system growth, but increased the total amount of soil microorganism. The good control of nutrient release contributed to reduced nutrient leaching, improved nutrient use efficiency of the fertilizers, and thus to homogeneous lawn growth and improved lawn quality.Pot experiments on ryegrass and Festuca arundinacea and plot experiment on Trifolium repens L were conducted to study effects of some CRFs (Shandong Kingenta Engineering Co., Ltd) on lawn production and nutrient leaching at varied N application rates as compared to conventional fertilizers. Another purpose of this study was to see the effect of CRFs on environmental quality and thus provide guidelines for application of CRFs on lawn production. The main results were as follows:The forming density of ryegrass, Festuca arundinacea and Trifolium repens L were less affected by fertilization and the fertilizer types, but higher fertilizer application rates could cause seedling salt damages and diminished lawn density. An increment of grass ramification could be observed across all treatments, fertilizer treatments greater than no fertilizer control (CK), and CRF treatments higher than conventional fertilizer treatments. Growth rates of ryegrass and Festuca arundinacea during entire growth season in fertilizer treatments were significantly higher than that in CK treatment; No much difference in growth rates across fertilizer treatments in earlier growth period, but a diminishing rate in later period could be observed. In ryegrass experiment, the grass height and growth rates were the greatest in Kf1 treatment compared to other treatments, and biomass per pot was 480.66 g, which was 58 % higher than that in Urea, and 82.9 % higher than CK. Festuca arundinacea experiment showed that CRU2 was optimal and the grass was about 1.5 m higher that that in Urea2 treatment at the 150^th day.The lowest growth potential of ryegrass was CK throughout entire growing season and was 1.5-2 times lower than fertilizer treatments; Besides, green degree was least in CK and greatest in Kf1 treatment. Trifolium repens L experiment indicated that the growth potential in CRU2>CRF1>Urea with the same N application rates. At the 150th day, the chlorophyll content of CRU1, CRU2 and CRU3 were 16.66%, 27.62%, and 26.60% greater than CK, and 9.39%, 12.75%, 12.22% greater than Urea1, Urea2 and Urea3 respectively. After lawn formation, the CRF2 and CRF3 maintained best growth potential in Festuca arundinacea, and had better laminae texture than other treatments. Greatest leaf chlorophyll a and b content was observed in CRF3, and least in CK, and there were great chorophyll content decrease during later period in CCF treatments compared to CRF treatments.The Trifolium repens L experimental results showed that controlled release urea achieved 100% cover percentage more rapidly, except for low cover percentage and homogeneity in higher rate treatments due to seedling salt damage. No marked difference in grass homogeneity existed between rates for the same fertilizer, and controlled release urea was superior to conventional urea at the same N rate, of which CRU2 scored above 8 was optimal in homogeneity after lawn had been formed. High fertilizer rate could inhibit root growth. At the same N application rate, the R/S ratio of CRU2 was 0.591unit, which was 0.148 unit higher than Urea2; CRU2 also had highest root vigor of 396.55 ug.g^-1FW.h^-1, which was 16.9%, 23.6% and 27.9% higher than CRU1, CRU3 and Urea2.respectively.Followed by CCF, CRF3 had highest NR content of 10.98 ug.g^-1h^-1, which was 108.7% higher than other treatments on average. The soluble sugar content of CRF3 was 48.2% and 70.1% higher than CCF and CK. The Trifolium repens L experiment showed that CK, CRU3 and Urea3 had higher MDA content in response to environmental adversity, e.g. nutrients deficiency and seedling salt damage; CRU1 and CRU2 had less MDA content than Urea1 and Urea2 at the same N rate. The NR content of CRU2 was 29.87 ug.g^-1h^-1, which was 5.33 greater than U rea2. The medium N rate had greatest NR content among three nitrogen levels for one fertilizer, and high N rate had least NR. Changes of the Soluble Sugar and amylum content was the same as NR, with medium N rate highest, high N rate least for one fertilizer, and controlled-release Urea better than Urea.Leachate pH and EC in all treatments decreased with leaching times. At day 30, leachate EC in Urea treatment were26.6%-63.1% higher than that in four CRF treatments because of its rapid nutrient release. NO₃-N concentration in leachate of different treatments increased initially and then decreased. Leachate NO₃-N concentration changed with fertigation in urea treatment, which amounted to greatest N leaching and was 24.9% greater than that in CRF treatments. In Trifolium repens L experiment, soil pH first declined and then gradually stabilized, while CRF treatments had less fluctuation than Urea. Compared to pH, soil EC changed in the opposite way. Soil NO-3-N content increased with N application rate increment at the same sampling time, and CRF treatments were more stable change while Urea reduction rapidly in the later period. Changes of soil NH₄^- N content were the same as NO₃^--N.