An on-farm survey of plant population of one year old, yet highly
productive alfalfa (Medicago sativa L.) swards in Khartoum North area, revealed that the plant population after one year from establishment, was equal to that resulting from a seed rate of I .5 kg/ha (i.e. 2.8% of the sown seeds). This suggested that the optimum seed rate for the production of each of the forage and seed of alfalfa in Sudan should be reconsidered. In this context, an experiment was conducted at Hudeiba Research Station for three years during the period of Dec. 1995 - January 1998 to study the time course forage and seed yield patterns of alfalfa sown with five low seed rates (i.e., 2.4, 4.8, 7.2, 9.6 and 12 kg/ha). The results indicated that the highest seed rate (12 kg/ha) produced the highest forage yield in a few cuts only. The variations among the time course forage yields of the various seed rates over the two years were either nonsignificant or enatic. The cumulative annual forage yield of the two higher seed rates, (9.6 &nbsp;and 12 kg/ha) was invariably higher than those of the other seed rates. For seed yield, the lowest seed rate (i.e., 2.4 kg/ha) resulted in the highest seed yield in the first two seed production cycles (SPC) in 1996 as well as in the annual total of the first year. Differences among the seed rates in other SPCs as well as the annual total of 1997 were either lacking or erratic. It is therefore, concluded that for dual purpose (forage and seed) alfalfa, the seed rate should not exceed 9.6 kg/ha, and for seed production the seed rate of 2.4 kg/ha is the optimum

A. A. Tambal, Hassan A. A. Tambal

A. M. Khair, Mohamed

English

Journals Of University Of Gezira

Gezira J. of Agric.  Sci. 3(1): 44-52 (2005)   44  Effect of Low Seed Rate on Seed and Forage Yield of Alfalfa in the River Nile State, Sudan  Hassan A. A. Tamball and Mohamed A. M. Khair2  1 Hudeiba Research Station, River Nile State, Sudan. 2 National Coordinator of Forage and Pasture Research Program,  ARTC, P(). Box 126, Wad Medani, Sudan. ABSTRACT An on-farm survey of plant population of one year old, yet highly productive alfalfa (Medicago sativa L.) swards in Khartoum North area, revealed that the plant population after one year from establishment, was equal to that resulting from a seed rate of I .5 kg/ha (i.e. 2.8% of the sown seeds). This suggested that the optimum seed rate for the production of each of the forage and seed of alfalfa in Sudan should be reconsidered. In this context, an experiment was conducted at Hudeiba Research Station for three years during the period of Dec. 1995 - January 1998 to study the time course forage and seed yield patterns of alfalfa sown with five low seed rates (i.e., 2.4, 4.8, 7.2, 9.6 and 12 kg/ha). The results indicated that the highest seed rate (12 kg/ha) produced the highest forage yield in a few cuts only. The variations among the time course forage yields of the various seed rates over the two years were either nonsignificant or enatic. The cumulative annual forage yield of the two higher seed rates, ( 6.9  and 12 kg/ha) was invariably higher than those of the other seed rates. For seed yield, the lowest seed rate (i.e., 2.4 kg/ha) resulted in the highest seed yield in the first two seed production cycles (SPC) in 1996 as well as in the annual total of the first year. Differences among the seed rates in other SPCs as well as the annual total of 1997 were either lacking or erratic. It is therefore, concluded that for dual purpose (forage and seed) alfalfa, the seed rate should not exceed 9.6 kg/ha, and for seed production the seed rate of 2.4 kg/ha is the optimum.       H. A. A. Tambal and M. A. M. Khair   44  INTRODUCTION Alfalfa farmers in the Sudan tend to use extremely high seed rates, mostly about 53 kg/ha, and few studies have been conducted to address this problem. For instance, Nayel and Khidir (1995) reported that forage yield was highest when 40 kg seeds were used compared to 30 or 50 kg/ha. On the other hand, Salih (1994) found that 12 kg/ha was the best compared to 24 or 36 kg/ha. In accord with Salih (1994) findings, Khair (7661 ) found no significant differences in forage yield of several seed rates within the range of 12-72 kg/ha. Accordingly, he suggested 12 kg/ha or lower as the optimum seed rate. The common practice in Sudan is to grow alfalfa for forage for the first two to three years then during .March - May of the 3rd or 4th year, the crop is left to produce seeds (Nayel and Khidir, 1995). A possible rationale for that is the progressive loss of plants during the first two years of the crop age which makes the plant population of the 3rd year optimum for seed production. The time course population dynamics of alfalfa during the establishment year showed that the calculated seed rates for the persisting plants are 7-8 kg/ha at the age of two months and only 3-4 kg/ha at the age of 10 months (Khair, 1997). A survey in farmers' fields in Khartoum North area revealed that the persisting plants in several one year old fields were equivalent to that resulting from 1-2 kg/ha (Khair et al. 1998). The original seed rate was 53 kg/ha. Hence, the loss of a large number of plants through self-thinning is inevitable when unnecessarily high seed rates are used. The question of whether the optimum seed rate of alfalfa for seed and forage production could be reduced below 12 kg/ha needs to be elucidated. Such low seed rate may enable harvesting of the seeds during the alfalfa establishment year. The objective of this study was, therefore, to investigate the time course forage and seed yield patterns as well as the annual total yields at seed rates ≤ 12 kg/ha. MATERIALS AND METHODS A field experiment involving alfalfa, (Medicago sativa L.) was conducted in the Hudeiba Research Station Farm (Lat. 70 34' N, Long. 330 56' E) during the period 17 Dec. 1995 to early 1998. The land was   Effect of Low Seed Rate on Seed and Forage Yield of Alfalfa in   44  prepared by disc ploughing, disc harrowing, leveling and ridging to 60 cm. The treatments comprised five seed rates (viz 2.4, 4.8, 7.2, 9.6 and 12 kg/ha) which were randomly allocated in a randomized complete block design with four replications. The plot size was  6.0 x 4.2m with 7 ridges.   Seeds were drilled on the top of the ridge to a depth of 3-5 cm and irrigated immediately. Further irrigations were at intervals of 7-10 days. Urea was applied at the rate 93 kg/ha prior to the third irrigation. The plots were kept weed free by hand weeding.  In each plot, the two outermost ridges were left as margins. The middle ridge was also considered a margin to divide each plot into two halves, each consisting of two ridges for either forage or seed yield. The net area each was 7.2 m2 . The forage was cut every four weeks and hence the number of cuts were 12 for 1996/97 and for 1997/98, seasons. In each at, the fresh matter was immediately weighed in the field.. A sub-sample of one kilogram was then oven-dried for dry matter determination. Seeds were harvested throughout each year in cycles referred to as seed production cycles (SPC). The SPC denotes the gestation period for each seed yield. Hence, there were 4 and 5 SPC in each of 1996/97 and 1997/98 respectively. At each seed harvest, pods were collected when 90 %or more of them were dry. They were then sun dried, hand threshed and weighed. Data on forage and seed yield of each year were statistically analyzed as for a split plot design: Cutting months (in the case of forage) and SPCs (in the case of seed yield) were considered main plots, whereas the seed rates were considered sub-plots in both cases. RESULTS Forage yield The differences in the dry matter yields among the various seed rates as well as among the cuts (over all seed rates) with the advancement in crop age )Table l) were either non-significant or significant in an inconsistent trend. The inconsistency resulted from the lack of a specific yielding trend of the seed rates, although they were equally spaced over a range of five levels. In eight out of the 24   H. A. A. Tambal and M. A. M. Khair   44  cuts (cumulative of both years), the differences among the seed rates were not significant. In only three cuts, however, did the highest seed rate (12 kg/ha) give the highest forage yield. The differences among the other seed rates in those three cuts were, however, not significant. In the remaining 13 cuts, no specific trend was observed, but the highest forage yield was associated with both 9.6 and 72.1 kg/ha in some cuts and with 4.8-12.0 kg/ha in others. The monthly and the annual cumulative dry matter yields of the various rates are shown in Table l. In 1996/97, the seed rate of 4.8 kg/ha    resulted in significantly the lowest monthly mean and annul cumulative dry  matter yields. The respective yields of the 12 kg/ha on the other hand,was significantly higher than those of all other seed rates except of 9.6 kg/ha. Likewise, in 1997/98, 9.6 and 12 kg/ha significantly outyielded both 2.4 and 4.8 kg/ha.  Seed yield As in the case of forage yields, the seed yield resulting from the different seed rates varied considerably with the advance in crop age )Table 2). In the first SPC of 1996, which occurred during the first 5 months of the crop age, and the second SPC of 1997, the lowest seed   Effect of Low Seed Rate on Seed and Forage Yield of Alfalfa in   44  rate (i.e., 2.4 kg/ha) resulted in the highest seed yield. In other advanced SPCs, differences among the seed rates, even-though significant in some cases, were non consistent among the SPCs. What was consistent however, was the superiority of the lowest seed rate (2.4 kg/ha) in the high seed yielding SPCs, viz the first in 1996 and the second in 1997. The annual cumulative (total) seed yields of both years, however, revealed limited differences among the seed rates. DISCUSSION The effective forage production age of alfalfa, in this study, i.e., the first cut, as well as in those of Nayel and Khidir (1995) and Khair (1997(, was staffed when the crops were 2-3 months of age. It is, therefore, the population of alfalfa at this stage and onwards which crucially contribute to the forage and seed yields. In an earlier study (Khair, 1997), when an average of 42 kg/ha of seeds were sown, the persisting plants at 3 and 10 months of age represented about 7-8 and 3-4 kg/ha, respectively. Despite the reduction in the plant population, the time course forage yield either remained more or less constant or increased in some cases (Khair, 1997( This agrees with an on-farm survey in Khartoum Nonh (Khair et. al, 7661 ,) which revealed that the productive plants of alfalfa which persisted after one year could have resulted from sowing about 1.5 kg/ha of seeds (2.8%ofthe sown seeds(.                H. A. A. Tambal and M. A. M. Khair   44  Table 2. Time course of alfalfa seed yield (kg/ha)as affected by seed rate   Seed production cycle  Seed rate (kg/ha) Mar-May 1996  Jun.-Jul. 1996 Aug.-Sep. 1996 Oct. -Dec. 1996 Annual Total 2.2 926  796 751 2 912 2.1 919  799 772 9 519 1.2 997  57 712 9 591 6.9 292  721 799 5 552 72.1 251  726 292 77 926 SE(±)   5     Jan-Feb. 1997 Feb-May 1997 June-Aug. 1997 Sep.-Oct. 1997 Dec.-Jan. 1998 Annual total 2.2 22 299 211 92 77 551 2.1 21 291 219 12 77 519 1.2 25 225 299 51 71 512 6.9 26 295 216 772 2 516 72.1 91 225 769 65 75 597 SE(±)   2     Based on the foregoing discussion, the limited or even enatic differences among the seed rates used in this study (Table l) were usual. The lack of significant differences in the forage yields among the seed rates of some cuts, along with the non-consistent differences in some others, might indicate that the initial population in each seed rate was reduced and that certain population equilibrium was attained in all seed rates. A similar observation was reported by Khair (1997) where no significant differences were found among the forage yields of several seed rates which ranged from 12-72 kg/ha. The theoretical initial population of the lowest seed rate of this study (i.e, 2.4 kg/ha) was about 1,056,000 plants/ha. The profusely growing new stems from the crown of a 3 months old alfalfa plant make the alfalfa canopy resembles that of clitoria, a popular forage legume in Sudan. It is, therefore, logical to assume that the optimum plant population for both clitoria and alfalfa at 9 months of age would be comparable. The optimum for clitoria (264,000 plants/ha) (Khair, 1999), however, constitutes 25% of the initial population of the alfalfa even when sown at 2.4 kg/ha. Despite the relatively lower seeds rates this study, the   Effect of Low Seed Rate on Seed and Forage Yield of Alfalfa in   45  time course monthly average forage yield of this study (Table 1) was even higher than that repotted for higher seed rates (Khair 1997) and compared closely with that reported for the extremely high seed rates reported by Nayel and Khidir (1995). Likewise, the annual total yields even in the lowest seed rate (2 4 kg/ha) of this study were higher than those reported by Khair, (7661 ) and comparable with those reported by Nayel and Khidir (1995).  Even in the case of the few significant differences, the magnitude of the differences were not high enough to justify the use of higher rates of such expensive seeds.  The highest seed rate (i.e., 12 kg/ha) outyielded the other seed rates in few cuts and both 12 kg/ha and 9.6 kg/ha outyielded the other seed rates in the cumulative annual total forage yields (Table l). Those two seed rates however, compared closely with 11 kg/ha which is recommended for the northern parts of the United Sates (Tesar and Jackobs, 1972) and with 8-15 kg/ha which is recommended for Australia (McDonald and Waterhouse, 1989). On the other hand, they are a little lower than 20 kg/ha recommended for pans of the United States (Miller, 1984(. The progressive reduction in the plant population of alfalfa with the advancement in the crop age (Khair, 1997 and Khair et al., 1998(, confines the differential response of forage and seed yields to varying seed rates, to the early ages of the crop. In agreement with that, the lowest seed rate (i.e. 2.4 kg/ha) resulted in the lowest forage yield in the first cut (Table l) but in the highest seed yield in the first SPC (Table 2). In contrast, 9.6 and 12 kg/ha resulted in the lowest seed yield. This is consistent with the observation of Decker, (1972) that relatively higher seed rates are usually used for forage than for seed production.  Furthermore, the high seed yield of the lowest seed rate in the firs SPC of this study (Table 2) agrees with the 1-3 kg/ha of seeds recommended for the seed production (Heath et al., 1985). The tendency of the farmers in Sudan to grow alfalfa for forage production during the first two-three years the produce the seeds in the third-fourth year could be attributed to the optimum population which   H. A. A. Tambal and M. A. M. Khair   45  resulted from the continuous reduction in the plant population for the seed production. As the case in the forage yields (Table1), lack and/or non consistent differences among the seed yields of the various seed rates in several SPCs were obtained. This could be due to the time course reduction of population which in turn might have nan-owed the differences among plant populations of the various seed rates. The relatively lower seed rates of this study had enabled the harvest of seed during the establish-ment year. This implies that farmers in the northern parts of Sudan, where forage is not highly needed, can use low seed rate to specialize in alfalfa seed production. The cumulative seed yield of this study, (Table 2) is higher than the 500 kg reported for California (Heath, et al., 1985(. In conclusion, the highest seed rate (12 kg/ha) produced the highest forage yield in only few cuts. The time course monthly forage yield of the various seed rates over the two years were either non-significant or enatic. The cumulative annual total forage yield resulting from 9.6 and 72  kg/ha were higher than those of the other seed rates. For seed yield, the lowest seed rate (i.e. 2.4 kg/ha) resulted in the highest seed yield in the high seed yielding SPCs as well as in annual totals. Differences among the seed yields of the various seed rates in other SPCs were either lacking or enatic. REFERENCES Decker, A. T H. Taylor, and C. J. Willard, 1973. Establishment of new seedlings. Pp384-395. In: Forage, the Science of the Grassland Agriculture. Heath M. E; D. S. Metcalfe, and Barnes, R.. F. (eds.). The Iowa State University Press, Ames, Iowa, USA. Heath, M. E, R.F. and DS. Metcalfe. 1985. Forages. 4th edition. Iowa State University Press. Ames Iowa, USA. Khair, M. A. M, H A A. Tampal, A o. Hossain and MH M. Salih. 1998. Forage yield of alfalfa (Medicago sativa. L) as affected by different seed rates. A paper presented at in the Crop Husbandry Committee Meeting, ARC, Wad Medani, 1998.   Effect of Low Seed Rate on Seed and Forage Yield of Alfalfa in   45  Khair, M. A. M. 1997. Effect of seed rate on plant population and forage yield of alfalfa on heavy clay Soils in Sudan. University of Khartoum Journal of Agricultural Sciences 5(2): 23-36. Khair, M. A. M. 1999. Principles of Forage Production. Training and Publishing Administration, Agricultural Research Corporation, Wad Medani, Sudan (in Arabic(. McDonald, W.J. and D. B. Waterhouse. 1989. Lucerne for Pasture and Fodder. AGFACT P 2.2.25, NSW Agriculture and Fisheries. Australia.  Miller, D.A. 1984. Forage Crops. McGraw-Hill Book Company New York, St. Iowa, USA Nayel, B. A. and M.O. Khidir 1995. Effect of seed rate and fertilizers on fodder and seed yield of lucerne (Medicago sativa L.) University of Khartoum Journal of Agricultural Sciences          3(1): 24-46. Salih, M.  H. M. 1994. Fodder production of berseem under varying seed rates, cutting and irrigation intervals. Annual Report, Shambat Research Station (1993/94). Agricultural Research Corporation, Sudan.  Tesar, M. B. and J.A. Jackobs. 1972. Establishing the stand. P 415-433, In: Alfalfa Science and Technology. Hanson, C.H. (ed.) American Society of Agronomy, Iowa, USA. 

Effect of Low Seed Rate on Seed and Forage Yield of Alfalfa in the River Nile State, Sudan

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Effect of Low Seed Rate on Seed and Forage Yield of Alfalfa in the River Nile State, Sudan

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