JASP 3 -- 1985.pdf - International Herbage Seed Group

JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985 571983. Nitrogen studies in Lolium perenne grown for seed.Grass and Forage Sci. 38:97-105.12. Madsen, N.P. 1972. Combine harvesting of grass seed fromthe standing crop. Dansk Landbrug 3:(7)24-27.13. Wright, D. and P.D. Hebblethwaite. 1979. Lodging studies inLolium perenne grown for seed. 3. Chemical control of lodging.J. Agric. Sci., Camb. 93:669-679.The Influence of Environmental and Agronomic Factors on Floret Site Utilizationin Perennial RyegrassP.D. HebblethwaitetABSTRACTThis paper reviews some of the work carried out at theUniversity of Nottingham on environmental and agronomicfactors which affect floret site utilization in the ryegrass seedcrop. Low average temperature at anthesis was shown todecrease floret site utilization. Level, timing of nitrogen applicationand lodging influenced floret site utilization. The use ofgrowth regulators increased floret site utilization and yield. Thefuture role of chemical manipulation and its influence on floretsite utilization is discussed.Additional index words: florets, seed set, t4C-assimilate, growthregulators, macro-environment, nitrogen, water.INTRODUCTIONMuch work has been carried out on the development ofpotential yield in ryegrass seed crops (Anslow, 1963; Ryle,1964; 1966; Hebblethwaite, Wright and Noble, 1980;Hampton, 1983) but little on the utilization of that potential(Hill, 1980). Most ryegrass seed crops produce largenumbers of floret sites per unit area and therefore potentialyields. Estimates indicate that if all floret sites are utilizedyields of around 8 t ha-I would be achieved in most crops(Hebblethwaite et al., 1980; Hampton, 1983). Actual percentagefloret site utilization under farm conditions isusually only about 10% which results in yields of well under1 tha-t.Consequently this paper deals with environmental andagronomic factors affecting floret site utilization and notfloret production.ENVIRONMENTAL FACTORSAt the University of Nottingham an examination ofmacro-environmental factors during anthesis and its relationshipto yield of the perennial ryegrass seed crop ( cv.S.24) was carried out using data collected over a ten yearperiod (Hampton and Hebblethwaite, 1983). Minimumscreen temperature during the month of June, during theweek of anthesis and during the week after anthesis wassignificantly related to seed numbers and yield. This factoraccounted for over 70% of the variance in seed numbersrecorded. Although measurement of the macro-environmentis crude compared to micro-environmental measurementswithin the crop this finding which takes 10 differing seasonsinto account agrees well with micro-environmental responsesreported by others (Jones and Brown, 1951; Hill, 1971;1980). Consequently it must be assumed that low averagetemperatures at anthesis (i.e. below 8 C) are likely todecrease floret site utilization. Little is known why thisshould be the case and what sort of damage occurs. Furtherwork into the effects of low temperature on floret siteutilization needs to be carried out.The only other weather factor related to seed numberswas wind velocity in the week following anthesis where areduction was recorded with increasing velocity. Rainfall,radiation, and relative humidity had no significant influenceon seed numbers (Hampton and Hebblethwaite, 1983).Irriga-tion experiments have also indicated that water stressequivalent to a profile soil water deficit of 90-100 mm willhave little effect on floret site utilization (Hebblethwaite,1977). Excess water during the period of seed set anddevelopment can increase secondary tillering and this couldbe at the expense of seed fill and consequently decreaseyield.AGRONOMIC FACTORS1Reader in Agronomy, University of Nottingham, School ofAgriculture, Sutton Bonington, Loughborough, Leics. U.K. Receivedfor publication 3 December 1985.Nitrogen experiments have shown that increasing theamount of spring applied nitrogen can increase the numberof florets per unit area but percentage seed set can be