Study On Optimal Management Of Water And Fertilizer In Lolium Perenne For Turf Under Drought Stress

Perennial ryegrass(Lolium perenne L.)is one common high-quality cool-season turfgrass,which can produce considerable economic and ecological benefits,but its normal growth requires a lot of water,and China is the world’s most scarce one of the countries with water,the common perennial ryegrass lawn in the city is mostly due to lack of water and fertilizer,resulting in poor lawn quality and less than the expected planting effect.Therefore,it is of great significance to study the optimal management strategy of water and fertilizer in perennial ryegrass under drought stress.In this study,the commercial perennial ryegrass variety of"Emerald"was used as the experimental material and the following four experiments were conducted.(1)A hydroponic experiment was conducted to study the effects of different forms and concentrations of nitrogen on the growth and physiological characteristics of perennial ryegrass under drought stress,and determine the better nitrogen form and concentration to relieve drought stress;(2)A hydroponic experiment was carried out using the better nitrogen form in test(1)to study the effects of nitrogen,phosphorus,and potassium fertilizer ratio application on the growth and physiological indicators of perennial ryegrass under drought stress,and determine the optimal nitrogen,phosphorus,and potassium ratio concentration;(3)Based on the optimal concentration of nitrogen,phosphorus and potassium in test(2),a Pot plant experiment was performed to explore the effects of different concentrations of water-retaining agents and fertilizer(nitrogen,phosphorus and potassium)on the growth and physiology of perennial ryegrass under drought stress,and to determine the optimal concentration of water-retaining agents and nitrogen,phosphorus,and potassium.(4)A pot plant experiment was performed to explore the effect of the optimal ratio of nitrogen,phosphorus and potassium and the concentration of water-retaining agent in test(3)on the growth physiological indicators of perennial ryegrass under the assumption of drought hardening,and explore the relationship between fertilizer and water-retaining agent interactions and their role in drought hardening.The main results are as follows:(1)The effects of different nitrogen forms on various indices of of perennial ryegrass under severe drought stress were different.Calcium nitrate in 9.8 mmol/L performed the best in increasing the aboveground biomass of perennial ryegrass.The total leaf surface area and leaf length under this treatment increased by 31.04%and53.87%respectively compared to the non nitrogen applying control;12 mmol/L ammonium sulfate performed the best in reducing the relative conductivity of perennial ryegrass leaves and increasing the chlorophyll content,which decreased by54.65%and increased by 26.51%respectively,compared with the nitrogen-free treatment;and 27 mmol/L urea attained the best in increasing the relative water content in leaves,which was 31.04%higher than that of non nitrogen applied treatment.(2)Three different forms of nitrogen used can enhance the drought tolerance of perennial ryegrass.The comprehensive analysis of membership function method showed that the comprehensive effect of three kinds of nitrogen on alleviating the harm of drought stress to the growth of perennial ryegrass was as follows:ammonium sulfate>urea>calcium nitrate.(3)Under drought stress,the beneficial effects of nitrogen fertilizer on the growth indexes of perennial ryegrass was more significant than that of phosphorus fertilizer and potassium fertilizer.The maximum value of each growth index appeared in the medium nitrogen group,while the growth of the high nitrogen group was small,but the reasonable combination of nitrogen,phosphorus and potassium fertilizers was better.(4)Considering the mitigation effect and fertilizer efficiency of the three elements of nitrogen,phosphorus and potassium on perennial ryegrass under drought stress,the most reasonable combination of nitrogen,phosphorus and potassium fertilizers was determined as:ammonium sulfate 12 mmol/L,sodium dihydrogen phosphate 8 mmol/L,potassium chloride 10 mmol/L.(5)In the condition of sufficient soil moisture,the addition of water-retaining agent and the combined application of water-retaining agent and nitrogen,phosphorus,and potassium fertilizers had little effect on perennial ryegrass.When the soil water content is 55%of the maximum soil water holding capacity,the addition of 25 g/m~2of water-retaining agent can effectively relieve the physiological damage of drought stress on the growth of perennial ryegrass when no fertilization is applied,and the addition of 50 g/m~2when fertilization combined application of water-retaining agent and nitrogen,phosphorus,and potassium fertilizers can make the soil retain water and fertilizer.(6)When the soil water content is 55% of the maximum water holding capacity of the soil,the perennial ryegrass after drought hardening can increase the turf quality of perennial ryegrass under the treatment of relatively optimal nitrogen,phosphorus,potassium ratio and water-retaining agent concentration.And the relative water content of the leaves,the content of chlorophyll,and the relative conductivity,malondialdehyde,and proline content of the leaves are reduced under the treatment of relatively optimal nitrogen,phosphorus,potassium ratio and water-retaining agent concentration.