Optimization Of Nitrogen,Phosphorus,and Potassium Fertilization Rates For Integrated Turf Performance Of Overseeded Perennial Ryegrass And Bermudagrass

Turfgrasses are an important part urban and peri urban landscapes throughout the world.Perennial ryegrass（Lolium perenne L.）and bermudagrass（Cynodon dactylon L.Pers）are cool and warm-season turfgrasses that perform best in their respective seasons.However,in transitional climatic zones their growth and performance are highly restricted by abiotic factors and improper nutrition.Nitrogen（N）,phosphorus（P）,and potassium（K）fertilization play an important role in ameliorating abiotic stresses and maximizing turf performance.Therefore,modeling and efficient nutrient management strategies were used to optimize N,P,and K fertilization rates for integrated turf performance（ITP）of perennial ryegrass and bermudagrass under transitional climatic zone.The results of all the three studies are as following;1.Bermudagrass turf loss due to severe cold in transitional climates is a major concern.To overcome this problem,warm-season grass is often overseeded with a cool-season turfgrass.In this study,modeling and efficient nutrient management were used to evaluate this problem.A three-factor and five-level central composite rotatable design（CCRD）with a simulation of a regression model was used to optimize fertilization rates.The study investigated the combined effects of fertilization with N,P,and K on both the morphological and physiological attributes and on the ITP of overseeded perennial ryegrass.Fertilization with N and P significantly increased turf height,density,color,fresh and dry weights,while N,P,and K significantly affected turf cover,quality and winter-kill.The Spring transition was delayed by fertilization with N and P,and accelerated by fertilization with K.Photosynthesis（Pn）,transpiration（Tr）,and stomatal conductance（Gs）were considerably enhanced by fertilization with N,P and K.During two separate experiments conducted during two consecutive years,the optimal combinations of N,P,and K were N:30,P:24,K:9,and N:30,P:27,K:6 g m^-2.The major conclusion of this study is that a balanced nutrient application utilizing N,P,and K is key to enhancing the winter performance of perennial ryegrass.2.Overseeding perennial ryegrass turf on dormant bermudagrass in transitional climatic zones of the world experience severe reduction in growth and utilization.Short photoperiods with irregular low winter temperature due to climatic changes in transitional zones pose critical cold stress to overseeded perennial ryegrass,that has poor low temperature tolerance.Efficient nutrient management plays an important role in the plant response to abiotic stresses.Therefore,a three-factor and five-level central composite rotatable design（CCRD）with a regression model was used to study the combined effects of fertilization with N,P,and K.The study demonstrated substantial effects of N,P,and K fertilization on lipid peroxidation（MDA）,cell membrane damage（EL）,production of reactive oxygen species（ROS）（H₂O₂）,and their detoxification through enzymatic and non-enzymatic antioxidants in overseeded perennial ryegrass leaves under cold stress conditions.The results revealed that cold stress under the deprivation of N,P,and K fertilization amongst them N and P severely hampered perennial ryegrass stress tolerance.The MDA,EL,and H₂O₂ contents increased under deprivation of any mineral nutrient during cold stress conditions.Fertilization with N,P,and K,especially N and P profoundly decreased the MDA,EL,and H₂O₂ contents in overseeded perennial ryegrass leaves by activating antioxidants enzymes.Fertilization with N and P remarkably increased soluble protein,SOD,POD,and proline content,while fertilization with N and K significantly enhanced CAT activities.Moreover,the chloroplastic pigments including chlorophyll a,chlorophyll b,total chlorophyll,and carotenoids considerably enhanced by N and P fertilization.Notably,the damage caused by cold stress in form of elevated MDA,EL,and H₂O₂ contents significantly reduced by fertilization with N,P,and K,particularly N and P which were concomitant with higher activities of antioxidant enzymes in this study.Based on the results of this 2-years study,we conclude that efficient nutrient management of N,P,and K is the key to enhance cold stress tolerance of overseeded perennial ryegrass.3.Bermudagrass turf is the most widely used turfgrass in urban landscapes.Large amounts of fertilizer are usually applied for maximum turf performance.Relatively little attention has been paid to nutrient management strategies for urban landscapes.However,efficient nutrient management of bermudagrass turf is imperative for sustainable management of urban green spaces.The objective of this greenhouse study was to understand the interactive effects of N,P,and K fertilization on the ITP of bermudagrass and to optimize the amount of N,P,and K required for maximum turf performance.We used a three-factor and five-level central composite rotatable design（CCRD）with a simulated regression model.We found qualitative and quantitative relationships between bermudagrass and fertilization which significantly affected the ITP.Fertilization with N,P,and K significantly influenced the percent grass cover,turf height,shoot dry weight and total chlorophyll content.Fertilization with N and P significantly enhanced the tiller length,turf density,color,and total protein levels.Root length and dry weight were augmented with the application of K and P.3-D surface plots indicated significant interactive effects of NP,NK,and PK on the ITP.A simulation optimization and frequency analysis indicated that the optimal combined amounts of these nutrients were N:25.95²7.56 g m^-2,P:24.20²6.36 g m^-2,and K:3.12⁴.94 g m^-2.Our results suggest that optimized fertilization of bermudagrass turf is key to sustainable management of urban landscapes.