EFFECT OF METHOD OF SEED BED PREPARATION, MULCHING AND TIME OF PLANTING ON YAM IN WESTERN NIGERIA

R. Lal and S.K. Hahn*

SUMMARY

Mulching of yam seed beds reduced soil temperature and improved emergence, time of emergence, yield per hill and the total yield of Dioscorea rotundata yams on a sandy soil in Western Nigeria. Com­parison of mounds with ridged and flat seed beds showed that these different treatments had no significant effect on tuber yield. Planting about six weeks before the onset of the rains and the use of mulch is indi­cated as a good technique to obtain high yield.

RESUME

L'utilisation de paillis dans les lits de plantation reduit la temperature du sol et favorise la levee, Ie temps d'emergence, Ie rendement par poquet et Ie rendement global des ignames Dioscorea rotundata lorsqu'elles sont cultivees en sol sablonneux a I'Quest du Nigeria. Lorsque la comparaison a ete faite entre la culture en buttes et en lits de semis non eleves, les resultats ont montre que la difference de rendement en tubercules est peu sensible, qu'iI s'agisse de 1 'une ou de 1 'autre methode. La plantation six semaines avant Ie debut des pluies et I'utilisation de paillis permettent d'obtenir un rendement eleve.

RESUMEN

EI cubrimiento de almacigos de name redujo la temperatura del suelo y mejor6 la emergencia, el tiempo de emergencia rendimiento por cepa y rendimiento total de name, Dioscorea rotundata, en un suelo arenoso de Nigeria Occidental. La comparaci6n de camas con almacigos alomados 0 pianos demostr6 que no hay diferencia entre ninguno de estos tratamientos en cuanto al rendimento de tuberculos. La siembra, cerca de 6 semanas antes del establecimiento de las lIuvias y el uso de cobertura, se indica como una buena tecnica para obtener altos rendimientos.

INTRODUCTION

Yam cultivation in West Africa extends from the central Ivory Coast to the Cameroon mountains, in both the forest zone and the southern parts of the savannah' ,9. Annual production in West Africa is about 31 million metric tons, or two-thirds of the total world production.

Yams require about 8 months from planting to maturity, and need, depending on soil conditions, 1500 to 1800 mm of rain during the growing period6 . They have a shallow root system. In Western Nigeria, where the dry season occurs from November until March, 'early planting' is generally done during the period from November to February. It has been shown that yams planted from November to January give 30 percent higher yield than those planted at the onset of rains'3.

Yams are often planted on mounds. The size of the mounds depend primarily on soil depth and the depth of the water table'3. On sandy soils however planting is generally on flat beds". Planting of yams in trenches has been shown to be of advantage for shallow and stony soils8 ,'4. Experiments conducted at Wenchi and Ejurain Ghana showed that yams grown on ridges yielded more than those grown on mounds1~ In Puerto Rico planting on raised beds increased the yield.

Farmers of West Africa traditionally place a 'cap' of dried straw on the mounds over newly planted setts'2. Previous experiments in Ghana showed a favourable effect of mulching on yam production parti­cularly in the savannah zone2 ,4. In Nigeria, mulching improved emergence by 50 percent and the overall yield by 3.75 tons per hectare. Mulching immediately after planting as compared with mulching at a later date was advantageous. Soil temperature measuremer'\¥ taken at 2 p.m. showed temperatures of 37.5 and 400 C. respectively for mulched and unmulched plots . Mulching has been proved beneficial for both late and early yam plantings.5 .

·International Institute of Tropical Agriculture, Ibadan.

293

MATERIALS AND METHODS

A factorial experiment, involving three methods of seed bed preparation, two levels of mulching and three times of planting, was conducted at the International Institute of Tropical Agriculture (IITA). liT A is located about 30 km south of the northern limit of the lowland rain forest. Rainfall distribution is bimodal in Western Nigeria, with rains from April to July and from August to November. The experiment was con­ducted during 1971-72 on soil of Egbeda association derived from basement complex rocks. The soil has a sandy surface and a layer of angular and sub-angular quartz gravels in the horizon immediately below the surface horizon and below this a deep, red clay profile.

Three different kinds of seed beds, 10 x 2 m, were prepared from a disced field as follows: (1.) flat, natural level surface, (2) mounds or hillocks 50 cm high and about 150 cm in the base circumference formed by scraping up the surface soil, and (3) ridges, about 30 cm high made across the slope at a spacing of75 cm.

Mulching with rice straw at a rate of 4 tons per lectcre was compared with no mulching. There were two planting dates before the onset of the rains (Octcoer :0,1971 and February 1, 1972) and one at the start of the rainy season (April 15, 1972).

Two setts of the local cultivar 'Fele' of approxklately 50 g weight were planted 10 cm below the soil surface at each mound. For flat and ridged seed beds single setts were planted at 50 cm intervals within the row. Twenty setts were planted in each plot The e<perimental design was a randomized block with four repl ications.

Soil temperature was measured at 5 and 20 crrl depth at 7.30 a.m. and 2.30 p.m. in one replication for each treatment. The emergence count and the time of emergence were recorded for all plots individual treatments. Staking of the vines was done one week after emergence. Yams planted on October 30, 1971 were harvested on September 30, 1972 and the two later plantings were harvested on November 1, 1972. Tuber weight and number of tubers per plant and the total yield per plot were determined for each plot.

RESULTS AND DISCUSSION

A. Soil temperature

Methods of seed bed preparation and mulching had a clear effect on soil temperature (Figures 1 and 2). The highest temperature was recorded for ridges and mounds. Ridge mulching decreased the soil tem­perature between 5 and 13.5°C at 2.30 p.m. for 5 cm depth at various times during the growing season. Diurnal fluctuations in soil temperature at 5- and 20- cm depth were also highest for heaps and ridges being in the order of 15 to 1aoC. Mulching on flat beds not only gave the lowest maximum temperatures throughout the growing season but also reduced the diurnal temperature fluctuation.

B. Emergence

There was a significant effect of time of planting, mulching and methods of seed bed preparation on emergence (Fig. 3). Poor emergence for the early planting on October 30 may be due to high soil tempera­ture and dry soil conditions. Planting on the flat seed bed with mulching gave the highest emergence for the early planting. Emergence on unmulched plots was extremely poor for the first planting, irrespective of the methods of seed bed preparation. Due to more favourable soil moisture and temperature, emergence for the second and third planting was higher than that of the first planting. Mulching significantly improved yam emergence, not only for all the methods of seed bed preparation, but also for all planting dates. With flat planting, for instance, mulching improved emergence by 73.5, 7RO and 36.5 percent for the first, second and third planting respectively. Planting on the unmulched heaps and ridges for early planting was a total failure.

Time of emergence was also significantly affected by methods of seed bed preparation and mulching (Table 1). Emergence, in general, was the quickest for plantings on the flat Early planting gave the slowest emergence (due to the high soil temperature and drought) (Fig. 4). lV.ulching reduced the time to emergence for all the methods of seed bed preparation and dates of plantings (Table 1, Figs. 5,6).

C. Yield and yield parameters

Tuber size: Time of planting and mulching had a significant effect on tuber size (Fig. 7). The longer the growing

period, the larger the tuber size. Methods of seed bed preparation under these experimental conditions did not have a significant effect on tuber size, though planting on flat generally produced smaller tubers com­pared to plantings on ridge or mound. Mulching significantly affected tuber size for all the three plantings, and hence soil temperature seems to play the dominant role in determining the tuber size.

294

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Yield per hill: Yield per hill was also the highest for the early planting and mulching significantly improved the yield

per hill for all three plantings (Fig. 8) There was an eight-fold increase in yield by mulching on flat for the early plantings as compared to a total failure for unmulched heaps and ridges. Statistical analyses of the data for the number of tubers per hill also indicated a significantly favourable effect of mulching.

Total yield per plot: The highest yield was obtained for the February and the lowest for the April planting (Fig. 9). The

yield for the flat mulched plots was equivalent to 31.6, 41.6 and 8.4 tons per hectare for the plantings on October 30, February 1 and April 15 respectively. While there was no yield for the unmulched heaps and ridges for October planting, favourable soil temperature and moisture regime produced some yield, though small, for the two later unmulched plantings.

Mulching had a highly significant effect on total yield, irrespective of methods of seed bed preparation and time of planting (Table 2). Methods of seed bed preparation per se had no effect on total yield.

REFERENCES

1. Agboola, S.A. (1968) The traditional significance of yam in Yorubaland in pre-colonial times. Niger. Agric. J. 5. 59-62.

2. Anon. (1964) Report of the Ministry of Agriculture, Ghana, 1953-54.

3. Anon. (1955) Report of the Ministry of Agriculture, Ghana, 1954-65.

4. Baker, E.F. (1962) Rep. Crop Husb. Res. Sect. Minlst. Agric. Nat. Resourc. W. Nigeria 1961-2.

5. Campbell, J.S. et a1. (1962) Recent developments in the production of food crops in Trinidad. Trap. Agr. Trin. 39, 261-70

6. Costas, R.C .• et a1. (1968) Effect of various cultural practices in yields of yams In Puerto Rico. J. Agric. Univ. P. Rico. 52,356-61.

7. Coursey,D.G. (1967) Yams. Longman, London.

8. Coursey, D.G. (1971) The history and the possible future of yam cultivation in West Africa. Seminar Root and Tuber Crops in West Africa. liT A, lbadan, February 22-26, 1971.

9. Doku, E. V. (1970) Root crops in Ghana, Ghana J. Sci. 6, 15-36.

10. Morgan, W.B. (1955) Farming practice, settlement pattern and population density in southeastern Nigeria. Geogr. J. 121.138-50.

11. Owusu, P.M. et a1. (1969) Yam farming in Ghana. Ghana Fms. 13, 132-5.

12. Torto. J.D. (1956) The cultivation of yams in the Goldcoast. New Goldcoast Fms. 1,6-8.

13. Waitt, A.W. (1960) Yam trials. Fed. Dep. Agrlc. Res. Nigeria 1958-9. 13-14.

14. - - - - - - (1963) Yams, Dioscorea species. Field CropAbst 16,145-57.

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TABLE 1

Effect of method of seed bed preparation and mulching on time of emergence for different dates of planting yam setts

-----------------------------------------------------------------

Surface treatment

Mulched

Unmulched

Flat Heaps Ridges

Flat Heaps Ridges

Time in days to first emergence* Planted Planted Planted

Oct.30, 1971 Feb.l, 1972 Apri 1 15, 1972

75 26 30 127 40 30 122 32 31

148 48 37

+ 55 40

+ 52 50

-------------~----------------------------------------------.---~

* Average of four replications + No emergence

TABLE 2

Analysis of variance - table of F ratio effects of treatments on total yield

Variable

~1u1ching (M) Seed bed (S) M x S

F ratio for various planting dates Oct. 30, 1971 Feb.15~ 192! April 15, 1972

71.4 30.1 889.64 0.5 0.1

1.33 1.07

1.39

305

TABLE 2

Mean cumulative yields* or 'milked' and replanted setts expressed in kg fresh weight of tubers per plot and as percentages of controls or unmilked setts yield

A B C Species or cultivars

Milking treatment First planting date

Second Third planting and planting and milking date milking date

Yields % of Cumula~ % of Cumula- % of (kg) control tive yield control tive yield control

of milked of mil ked sett sett

(Aa) (b) (Aa) (b) (Aa)

1. D. rotundata a. control ( cv. Aga) b. milked setts 38.5 85.2 54.5 120.6 54.6 120.8

2. D. alata a. control 47.6 b. milked setts 40.8 85.7 59.8 125.5 61.6 129.4

3. D. dumetorum a. control 22.0 b. milked setts 20.3 92.3 24.0 109.1 24.0 109.1

4. D. rotundata a. control 35.6 ( cv. Abi) b. milked setts 42.2 118.5 56.0 157.3 56.4 158.4

5. D. cayenensis a. control 25.8 b. milked setts 23.6 91.5 23.9 92.6 23.9 92.6

* Mean yields are based on individual plots of 20 plants each replicated three times. ---------------------------------------------------------------------------------------------------. ----------------------------------------------------------------------------------------------------

306

TABLE 3

Mean yields* (in kg fresh weight of yam tubers) per plot and percentages of tuber yields from milked satts as compared with control (unmilked satts) yields at different planting and milking dates

Mean yields* (in kg fresh weight of yam tubers) per plot and percentages of tuber yields from milked setts as compared with control (unmilked setts) yields at different planting and

milking dates -----------~-----------------------------------------------------~--

Setts milking treatment

(a) control Yield(kg} Percentage

(b) mi 1 ked Yield(kg) setts Percentage

* Each yield figure is species or cu1tivars

B C Second Third

A First

planting date

planting and planting and milking date milking date

35.2 23.8 2.1 100 100 100

33.1 10.6 0.5 93.99 44.5 23.6

a mean of 20 yam stands of five yam replicated three times.