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

4 JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985Table 5. Effect of time of closing on Maku lotus seed yields in1981-82.Treatment(Closing date 1981)UncutSE (mean)12NovemberSE (mean)24November4December15 DecemberSE (mean)Seed yieldgm-2(12% moisture)47(4.8)1.2(0.25)001.5(0.47)Table 6. Effect of time of closing and method of cutting atclosing on Maku lotus seed yields in 1982-83.Treatment(Time of closing, 1982)29 September 198220 October 198211 November 1982SE (mean)SignificanceUncutMean of 6 cut treatmentsSE (mean)Significance!Linear 2Non-significant** Significance 1% level.Seed yieldCut to groundlevel28.213.66.74.24IL**48.825.85.8**g m-2(12% moisture)Topped39.941.125.97.392N.S.Topping produced significantly higher yields, than cutting atall closing dates.Pod shatter was rapid in 1981-82 as a result of hot dryconditions when harvesting was delayed. Uncut plots harvestedon 21 January 1982, had 11% of total seed on theground and eight days later 47% of total seed was on theground. Pod shattering was minimal in 1982-83 with only2% pod shatter in the uncut plots at harvest.Components of Seed YieldIn 1981-82 cutting reduced the number of umbels per stemand pods per umbel (Table 7). In 1982-83 seed yield per stemand seeds per pod when both topped and cut to ground level,showed highly significant (P < 0. 01) decreases from Septemberto November closing dates (Table 8). Cutting at groundlevel significantly (P< 0.01) reduced umbels per stem. Podsper umbel and 1,000 seed weight were not affected by successivelylater closings and severity of defoliation (Table 8).DISCUSSIONDelaying the date of closing and increasing severity ofdefoliation at closing depressed seed yields of Maku lotus.This pattern of reductions in seed yield following either lax orsevere defoliations, particularly after bud formation, has alsobeen reported in other herbage legumes e.g., Lotus corniculatus(Anderson and Metcalfe, 1957; Bader andAnderson, 1962), Medicago sativa (Kowithayakorn andHill, 1982), Stylosanthes guianensis (Loch et al., 1976), S.humilis (Loch and Humphreys, 1970; Fisher, 1973), Trifoliumsubterraneum (Rossiter, 1961; Collins, 1978) and Trifoliumpratense (Dade, 1966).Closing Maku lotus seed crops from November onwardssignificantly reduced seed yields as previously observed byClifford ( 1975; reported by Lancashire et al. , 1980). However,closing even earlier, in late September and October,with a close ground cutting, also decreased seed yields.These decreases of Maku lotus seed yields may be caused byeither slow recovery from severe defoliation, (Sheath, 1980)or slow growth under cool early spring temperatures(Charlton, 1977). In both trials warm spring temperaturesabove lYC were not reached until November.Both lucerne and white clover recover rapidly from defoliationand grow in the early spring when the average dailytemperatures are still about 10-15 C. Grazing can thereforebe practiced before closing crops for seed production. However,Maku lotus has relatively little winter or early springgrowth and therefore, spring grazing cannot be carried out ifmaximum seed yields are to be produced.Topping did not simulate mirid damage, as the stems didnot branch and produce more umbels per stem (Table 8) andconcentrate flowering. Instead there was a decrease in seedsper pod following topping. Clifford et al., (1983) found thatmirids only damaged the umbels. Topping in this studyremoved the umbels and 50-100 mm of stem, and this mayhave been too severe to allow Maku lotus to recover, branch,and produce more umbels per stem. However, it is impracticalfor farmers to remove any less stem by topping in Novemberor December, because of the height and unevengrowth of Maku lotus stands. There is a need, however, formore detailed study of the effect on seed yield on removingTable 7. Effect oftime of closing on components of seed yield ofMaku lotus in 1981-82.TreatmentUncutCut to groundlevel12 Nov24 Nov4 Dec15 DecSE (mean)Stemsm-232542734537334317.8Umbelsstem-t8.54.21.9Podsumbel-!8.05.22.61000seed wt(12%moisture)0.9300.9180.938