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2.5.5 Conservation tillage and erodibility

2.5.6 Weeding, labour use and returns

Chuma (1993) applied mulch ripping, clean ripping, no-till tied ridging and hand hoeing. No-till tied ridging and mulch ripping showed lower total soil loss than the other treatments. Checking the tillage effects five years (measured annually) after the treatments were applied, erosion and penetration resistance were evaluated by determining organic carbon content, percent clay in the upper root zone structural stability, infiltration and soil strength.

Conservation tillage treatments showed lower organic carbon reductions than conventional tillage, mulch ripping treatment however, showed slightly better structural stability than conventional tillage. Hand hoe treatment showed high soil strengths likely to inhibit root penetration.

Chuma (1993) concluded that minimal soil disturbance as by ripping operation combined with improved soil fertility and ground cover could contribute to improved erosion resistance. He confirmed fears that present tillage practices were depleting (maybe upto 2.5m tonnes/annum) organic carbon leading to increased erodibility.

Weeding is an important consideration in conservation tillage systems and can be a major shortcoming to the promotion and eventual adoption of Contil technologies. Riches et al. (1997) reported that weeding accounts for upto 60% of the labour used in maize production in semi-arid Zimbabwe (MLARR, 1992). Because of poor returns from cropping and an acute shortage of labour in many households, conservation tillage and weed control systems should be based on low cost, labour-saving technologies (Ellis-Jones and Mudhara, 1995). While 76% of households in southern Zimbabwe own a plough, only 23% own an inter-row cultivator (MLARR, 1992). Weeding is undertaken by plough, cultivator, hand hoe or a combination of methods depending upon implement ownership, draught power and labour availability. If a plough is used, farmers usually remove the body (mouldboard) leaving the share as the operational weeding blade. They recognise that timely inter-row cultivation is important for weed control and for maintaining a rough soil surface which can retain subsequent rainfall (Ellis-Jones and Riches, 1992).

1993/94*

Hand weeding

2251

126

0

126

17.9

Cultivator

2092

45.3

15.1

60

35.0

Plough w/ body**

3047

20.3

36.8

57

53.5

Plough less body

1636

45.3

36.3

82

20

Manual

Mechanical

Total

1992/93

132.5 52.2 26.8 45.4

0 16.2 28.3 40.4

132.5 68.3 55.2 85.8

1994/95

Hand weeding

3670

155.6

0

155.6

23.6

Cultivator

3990

42.6

13.5

56.1

71.1

Plough w/ body**

3896

0

34.6

34.6

112.6

Plough less body

2590

41.4

34.7

76.1

34.0

Table 5: Maize grain yields (kg ha-1) labour requirements for weeding (h) and return to weeding labour (kg yield h-1) for four weeding systems at the Makoholi Experiment Station.

*labour for hand weeding estimated from on-farm records; ** ridges were tied after weeding in 1993/94 and 1994/95.

Weeding by mechanical systems required less labour than hand hoeing (Table 5). With the body removed the plough had an effective working width of only 25cm so three passes

were needed to weed each inter-row. The plough with body system gave the greatest return in terms of maize grain yield per weeding hour (Table 5), even when the plough system resulted

Hand weeding

5195

Cultivator

4552

Plough with body

4345

Plough less body

2766

Return to weeding

39.3 66.7 78.7 32.5

Labour requirement for weeding

14,

This paper is published in: Kaumbutho P G and Simalenga T E (eds), 1999. Conservation tillage with animal traction. A resource book of the

Animal Traction Network for Eastern and Southern Africa (ATNESA). Harare. Zimbabwe. 173p. A publication supported by French Cooperation, Namibia. For details of ATNESA and its resource publications, see http://www.atnesa.org

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