In¯uence of tillage systems and seedbed types on sorghum
yields and economics in northern Ghana
R.A.L. Kanton
a,*, O. Frimpong
b, P. Terbobri
a, A.S. Sadik
c,yaManga Research Station, Savanna Agricultural Research Institute, PO Box 52, Tamale, Ghana bSoil and Water Management Division, Soil Research Institute, Academy Post Of®ce, Kwadaso, Kumasi, Ghana
cFaculty of Agriculture, University for Development Studies, PO Box 1350, Tamale, Ghana
Received 13 November 1998; received in revised form 14 July 1999; accepted 28 February 2000
Abstract
Inappropriate tillage practices and seedbed types have often been identi®ed as major constraints to cereal crop production in the Savanna agro-ecological zone of northern Ghana. In an effort to increase crop production and conserve the soil from degradation, through mechanical manipulation of the soil, ®eld experiments were conducted from 1992 to 1995 to study the effects of tillage systems and seedbed types on performance of sorghum (Sorghum bicolor(L.) Moench), weed infestation, and tillage economics. The tillage methods evaluated were: manual, bullock, and tractor and the seedbeds studied were: ¯at and ridge. The highest sorghum grain yield was recorded in 1994 for tractor ridge with manual ¯at recording the least in 1995. Tractor and bullock tillage systems recorded a mean increase in sorghum grain yield of about 42% over manual tillage. Mean increases in grain yield recorded by ridge seedbeds over their ¯at counterparts for different tillage systems for the 4 years were: manual, 176%; bullock, 57%; tractor, 54%. Bullock ridging gave the highest straw yield in 1992 with manual ¯at recording the least in 1995. Ridges for all tillage systems recorded signi®cantly higher straw yields compared to their ¯at counterparts. Weed infestation was signi®cantly (p<0.05) higher for manual tillage and the least for tractor tillage under both seedbeds. Mean weed populations recorded for the tillage systems were: manual, 508 weeds mÿ2; bullock, 358 weeds mÿ2; tractor, 242 weeds mÿ2. Bullock ridging resulted in the highest gross margin with the least obtained for manual ploughing. #2000 Elsevier Science B.V. All rights reserved.
Keywords:Gross margin; In®ltration; Seedbed; Sorghum; Tillage
1. Introduction
Results of tillage work carried out under the semi-arid environment in West Africa often recommended
the need for some degree of tillage. However, when comparing results, it is important to take into con-sideration the soil type and rainfall pattern (Nicou, 1979). Chopart (1981) and Chopart et al. (1981), summarising results from extensive work carried out in Senegal, Togo and Ivory Coast, concluded that mechanical tillage has bene®cial effects on structu-rally inactive soils. These soils are quite extensive in the semi-arid areas in West and East Africa. Conse-quently, generalisation of tillage for large areas with-*Corresponding author. Present address: Department of
Agri-cultural Botany, School of Plant Sciences, University of Reading, PO Box 221, Reading RG6 6AS, UK.
E-mail address: [email protected] (R.A.L. Kanton)
yDeceased, 1999.
out due consideration of the soil type is bound to result in many errors and disappointments. Tillage is loca-tion and crop speci®c.
The use of animal or tractor power for deep tillage in the dry lands of West Africa has several advantages in terms of timeliness of operation, water in®ltration, weed control and deeper root growth (Malek et al., 1973). Charreau (1974) estimated the land area that could be cultivated by hand hoe, one horse, a pair of oxen, and a tractor as 1, 6, 10 and 25 ha per day, respectively. Charreau (1977) concluded that deep tillage is particularly important for ferruginous tropi-cal soils, which are prone to severe weed infestation and have a high content of ®ne sand. Under these conditions, ploughing proved to be the most ef®cient tillage practice. Comparing untied ridges and ¯at bed con®gurations in a mixed cropping system in the Guinea Savanna zone, Kumar et al. (1987) concluded that overall system productivity was marginally higher in the ridge system, but that the yield differences were not signi®cant.
The use of machinery for ploughing has increased in recent times; however, without basic information on soil suitability, there are many constraints associated with the introduction of these machines for land preparation. As a result, soil degradation and erosion have increased in some areas in Africa (Ofori, 1995). In northern Ghana, particularly in the Upper-East Region, about 65% of the farm families own or hire draft animals. The use of animal traction is intensive and has a long history in the region dating back to the 1930s. Considering the importance of tillage and seedbed in any cropping system, research is needed to evaluate the various tillage systems and seedbed types in northern Ghana. The objective of this study is to evaluate the existing tillage systems and seedbed types, and assess their agronomic and economic advantages for increased and stable sorghum produc-tion.
2. Materials and methods
2.1. Experimental site
The experiments were conducted during the crop-ping seasons of 1992±1995 on the research plots of Manga Agricultural Research Station near Bawku in
the Upper-East Region of Ghana, located on latitude 118010N and longitude 00
8640±00
8±160W, with an altitude of 249 m above sea level. The soils of the experimental area are shallow, and located on gently sloping terrain of gradient 1±2%. The soils are sandy to sand loam by texture within the 0±30 cm depth and thus well to moderately well drained. They are clas-si®ed as Plinthic Lixisols according to the FAO± UNESCO classi®cation (Boateng and Ayamga, 1992). The gravel fraction is 10 g kgÿ1with inherently low fertility status (N 0.02±0.008 g kgÿ1, organic carbon 0.28 g kgÿ1, available phosphorus 1.6± 5.2 g kgÿ1). The pH of the soils (CaCl2) ranges from 5.0 to 5.8. The soils have been developed from parent material derived from biotite granite with intrusions of biotite gneiss. The mean annual rainfall from 1981 to 1992 is 960 mm, mostly distributed from May to September, with March and October recording 24± 30 mm of rainfall. Mean annual temperature is 28.58C. Average maximum temperatures are highest in March or April (40±458C), while absolute mini-mum temperature ranges from 15 to 188C, occurring in December and rarely in January. Climatic data during the experimental period are presented in Table 1.
2.2. Tillage and cropping experiments
The ®eld experiment was a 32 factorial, laid out in a split-plot design with four replications. The main-plot factor was tillage systems and the sub-main-plot factor was seedbed types. The tillage systems evaluated were: manual, bullock and tractor, and the seedbed types studied were: ridge and ¯at. The trial was planted in the third week of June of each cropping season. The test crop was a local sorghum cultivar ``Bawku-Red'' which has a maturity period of four months and is the most extensively grown sorghum in the area.
seed-beds, each implement was adjusted to a spacing of 0.75 m, as this is the standard practice. The manual ridge was like a pyramid in shape, tapering at the top, while the bullock and tractor ridges were similar in shape like a trapezium. The manual ridge was 53 cm wide at the base, 27 cm wide at the top, and 21 cm in height. The bullock ridge was 59 cm wide at the base, 30 cm wide at the top, and 19 cm in height. The tractor ridge was 76 cm wide at the base, 44 cm wide at the top, and 19 cm in height.
Sorghum seeds were sown at a rate of 4±6 seeds per stand, and later thinned to two plants per hill, two weeks after emergence. Compound fertiliser in the form of 15±15±15 at the rate of 30 kg N haÿ1, 30 kg P haÿ1
and 30 kg K haÿ1
, was applied exactly two weeks after sowing. Sulphate of ammonia was applied as a side-dress at the rate of 10 kg N haÿ1at exactly six weeks after sowing as recommended locally for sorghum. The spacing between rows in both the types of seedbeds was 0.75 m and spacing between plants was 0.30 m. Each treatment consisted of six ridges/rows with data taken from the middle four ridges or rows for planting on the ¯at one, leaving out the outer two ridges or rows. Weeding was done before applying the fertilisers.
2.3. Plant and weed measurements
Post-harvest data were taken on fresh and dry head weights, plant count at harvest, fresh straw weight, and head length. Plants from the middle four ridges or rows were harvested for post-harvest analysis. Weed samples were taken from a 1 m2area using a measur-ing tape at three random sites within the net plot area
and the average number of weeds taken. This was done prior to each weeding and the mean taken for analysis. Plant measurements were statistically analysed using ANOVA techniques, and mean separation using least signi®cant difference (LSD).
2.4. Economic analysis
For economic analysis, data were collected on labour input for the various operations under each tillage, cost of land preparation, and other operations for each tillage system. Cost of labour as well as the prices of sorghum and dry straw were also utilised. The total labour input was calculated in mandays (Md) as the sum for labour involved in all the operations for each tillage system. Costs were also taken to embody the total cost involved in land preparation and labour for all the other operations for each tillage system. In arriving at the gross margins, the straw was also taken into account since it is sold as fuel wood. This together with the value of the grain constituted the gross income.
3. Results and discussion
3.1. Weed infestation
There was a signi®cant (p<0.05) tillage effect on weed infestation in sorghum for all the years when the experiment was conducted (Table 2). In 1992, the highest weed infestation was recorded for manual ¯at with tractor ridge recording the least. Manual ¯at and ridge recorded a signi®cantly (p<0.05) higher weed
Table 1
Climatological data during the experimental period at Manga Agricultural Research Station
Temperature degree8C Rainfall (mm) No. of rainy days Minimum Maximum
1992 1993 1994 1995 1992 1993 1994 1995 1992 1993 1994 1995 1992 1993 1994 1995 June 23.3 24.6 23.6 24.4 33.3 34.6 32.7 34.4 158.0 209.9 64.3 156.7 11 11 7 7 July 22.8 22.9 23.3 24.4 31.6 32.0 32.0 32.1 158.7 113.1 147.6 182.4 11 9 12 12 August 22.5 22.4 23.1 22.5 30.9 31.5 30.8 30.7 186.4 157.4 339.3 330.1 17 11 18 19 September 22.3 22.5 22.9 23.2 31.8 32.5 31.8 32.3 164.2 105.1 209.4 89.6 15 10 14 12 October 22.4 23.4 22.7 23.0 34.8 35.8 33.3 25.4 35.6 20.1 229.5 47.3 5 9 14 6
infestation compared to their bullock and tractor counterparts. Similarly, bullock ¯at and ridge recorded a signi®cantly higher weed infestation compared to their tractor counterparts. In 1993, manual ¯at sup-ported the highest weed infestation and tractor ridge the least. Tractor ridge recorded a signi®cantly (p<0.05) lower weed infestation compared to the other seedbeds for all tillage systems. Tractor ¯at supported a signi®cantly (p<0.05) lower weed infestation com-pared to manual and bullock seedbeds. Bullock seed-beds also recorded a signi®cantly (p<0.05) lower weed pressure than their manual counterparts. In 1994 and 1995, trends were the same as for the previous years.
The higher weed infestation recorded for manual tillage system compared to bullock and tractor tillage systems might be attributed to the rather super®cial effect of the hoe resulting in poor weed control during land preparation. It is often argued that the main effect of the hoe on the soil is super®cial (Ofori, 1995).
Unger (1984), and Nitant and Singh (1995) reported that deeper ploughing allows maximum absorption of rainwater and reduces weed populations at the initial stage of crop growth, which ultimately increased crop yields.
3.2. Sorghum grain yield
There was a signi®cant (p<0.05) year effect on sorghum grain yield (Table 3). The highest sorghum grain yield was obtained in 1994, while the lowest was recorded in 1995. This is probably due to the higher rainfall and its more optimum distribution throughout the growing period (Table 1). Lower grain yields in 1995 was attributed to an outbreak of sorghum shoot ¯y, which resulted in many chuffy sorghum heads at harvest in 1995.
Tillage effect on grain and straw yields of sorghum was signi®cant (p<0.05) according to the analysis of variance table. Mean grain yield (kg haÿ1) recorded under the different tillage systems from 1992 to 1995 are: manual, 459; bullock, 701; tractor, 708. Bullock and tractor tillage systems consistently recorded higher grain yields compared to their manual counter-part for the experimental period.
Sowing sorghum on ridges for all tillage systems resulted in superior grain yields compared to sowing on the ¯at (Table 3). Mean increase in grain yield recorded by ridges over ¯at seedbeds from 1992 to 1995 are: manual, 175%; bullock, 54%; tractor, 54%. The superior sorghum grain and straw yields obtained for bullock and tractor tillage systems might
Table 2
Weed infestation (weeds mÿ2) in sorghum as affected by tillage systems and seedbeds, 1992±1995
1992 1993 1994 1995
Flat Ridge Flat Ridge Flat Ridge Flat Ridge
Manual 510 506 525 493 551 522 454 503
Bullock 370 342 378 360 155 308 392 359
Tractor 249 235 220 153 232 249 296 302
LSD (0.05) 57 57 59 59 92 92 72 72
Table 3
Sorghum grain yield (kg haÿ1) as affected by tillage systems and seedbeds, 1992±1995
1992 1993 1994 1995
Flat Ridge Flat Ridge Flat Ridge Flat Ridge
Manual 193 333 130 325 191 654 14 142
Bullock 211 466 241 375 533 612 105 261
Tractor 272 350 296 487 483 725 67 154
probably be attributed to the better weed control achieved by these tillage systems compared to manual tillage. Bullock and tractor tillage systems work the soil deeper than manual, thereby resulting in a better weed control as re¯ected in the lower weed popula-tions obtained for these tillage systems. Olufayo et al. (1994) reported a yield increase of 40% of sorghum grain due to ploughing compared to hand hoeing.
The volume of soil accumulated under ridges is relatively larger, thereby concentrating plant nutrients for better plant growth and development as indicated by the results obtained in this study. The results reported here also con®rm previous works carried out by Nicou et al. (1990).
Kumar et al. (1987) concluded that overall system productivity was marginal in the ridge system, but that the yield differences were not signi®cant. The use of animal or tractor power for deep tillage in the dry lands has several advantages in terms of timeliness of operations, water in®ltration, weed control and deeper crop root growth (Malek et al., 1973).
3.3. Sorghum straw yield
The highest sorghum straw yield for the experi-mental period was recorded in 1993 for bullock rid-ging and the lowest for manual ¯at in 1995 (Table 4). In 1992, bullock ridges recorded the highest straw yield with manual ¯at recording the lowest.
Mean straw yields (Mg haÿ1), recorded by the tillage systems over the experimental period were: manual, 9.2; bullock, 12.2; tractor, 10.7. The highest straw yield was recorded in 1993, while the lowest was obtained in 1995.
Mean increase in straw yields recorded by ridges over ¯at seedbed for the tillage system were: manual, 119%; bullock, 69%; tractor, 52%.
The superior straw yields obtained for bullock and tractor tillage systems over manual tillage and ridge seedbeds over ¯at ones could similarly be attributed to the earlier explanations given above for sorghum grain yields.
3.4. Economic analysis
3.4.1. Labour input
The highest labour input resulted from manual ridging and the least from tractor ploughing (Table 5). The labour input for bullock ploughing and bullock ridging was similar. In comparison, the labour input for manual ploughing and ridging was higher than the other tillage systems. This is due to the drudgery associated with manual operations, which are time and energy consuming. Ridging also resulted in higher labour input than ¯at.
3.4.2. Costs
Tractor ridging resulted in the highest cost, while bullock ploughing resulted in the least (Table 5). In tractor ridging, the ®eld has to be ploughed before ridging and this coupled with the high rates charged for tractor services resulted in the highest cost. Tractor ploughing also gave a higher cost than manual and bullock tillage systems as a result of the high costs for tractor services. The results also indicate that ridge tillage systems resulted in higher costs than ploughed tillage methods. This is due to the higher labour input involved in ridge tillage methods.
3.4.3. Gross margin
The bene®ts are the gross margins resulting from the different tillage systems. Bullock ridging was found to have the highest gross margin with the least
Table 4
Sorghum straw yield (Mg haÿ1) as affected by tillage systems and seedbed, 1992±1995
1992 1993 1994 1995
coming from manual ploughing. In all the three tillage systems, ridge seedbeds gave higher gross margins than ¯at seedbeds. Although the gross income for tractor ridging was the highest, bullock ridging still resulted in the highest gross margin. This is due to the high rates charged for tractor services and the fact that in the case of tractor, the land has to be prepared before being ridged. For the small-scale farmer, bullock ridging looks more promising since it is more afford-able than the tractor operations and the drudgery associated with it is also lesser than that of manual ploughing.
4. Conclusions
In this study, bullock tillage system and ridge seedbeds gave the highest grain and straw yields, and gave the highest economic returns. These results indicate that sowing on ridges is superior to sowing on the ¯at. Bullock tillage system gave best returns compared to tractor and manual tillage systems for all the years when the experiment was conducted from both agronomic and economic con-siderations.
Bullock tillage also attracts less operational charges as compared to tractor tillage and involves less drud-gery compared to manual tillage operations. Consid-ering the fact that the Upper-East Region of Ghana has about 20% of the country's livestock population, bullock tillage system and ridge seedbeds can easily be adopted for increased, stable and economic crop production.
Acknowledgements
The work reported here forms part of the approved research programme of the Upper-East Region Land Conservation and Small-Holder Rehabilitation Project (LACOSREP) with funds from the International Fund for Agricultural Development (IFAD). The authors are grateful to the Director of Savanna Agricultural Research Institute (SARI), for making facilities avail-able and permission to publish. The authors are also grateful to the Regional Director of the Ministry of Food and Agriculture, Upper East Region. Finally, the authors wish to express their gratitude to Ms. Fran-cisca Abbah for typing the script and Messrs. Anthony Nkrumah, Emmanuel Ansoba and Adamu Bukari for data collection.
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Table 5
Economic analysis of tillage systems and seedbed typesa
Tillage system Gross income (¢)
Total labour input (Md)
Cost of labour for land preparation and other operations (¢)b
Gross margin (¢)b
Manual flat 78911 68.38 72962 5949
Manual ridge 200032 74.54 79534 120498
Bullock flat 171800 62.56 72432 99377
Bullock ridge 78911 62.83 77270 156757
Tractor flat 165206 59.87 99109 66097
Tractor ridge 240947 65.80 212613 119334
aBased on following: prices: sorghum, ¢211.01 kgÿ1; dry straw, ¢32.48 kgÿ1; wage price of labour, ¢1067 Mdÿ1; land preparation charges
(haÿ1): bullock ¯at, ¢12 500.00; bullock ridge, ¢15 000.00; tractor ¯at, ¢17 500.00; tractor ridge, ¢37 500.00.
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