Figure 2. Young rye plants, approximately 6 weeks old. At this stage fertilisation with LAN will greatly enhance good dry matter production. Figure 1. The germination of Paraggio medic and vetch was the highest where the rotary harrow was used, probably as a result of the finer seed bed created by the implement.

Within the framework of integrated grape production it is important that the use of agrochemical products should be restricted to the absolutely essential.

Cover crop management is a biological means of controlling weeds pre-emergently. To obtain effective pre-emergence weed control with a cover crop, it is important to produce as much fibre as possible. Cover crop growth is influenced primarily by the climate (Fourie, Louw & Agenbag, 2001) and available water, i.e. irrigation and/or rainfall (Fourie & Louw, 2002). However, seed bed preparation techniques and the type of implement(s) used may also influence cover crop production.

The purpose of the study was therefore to determine the influence of various seed bed preparation techniques with a disc, a disc harrow (Fig 1), as well as a combination of the disc and a spike harrow (ghrop), on the establishment and dry matter production (DMP) of cover crops with various sizes of seed.

MATERIAL AND METHODS

Three cover crop species, namely rye (Secale cereale), vetch (Vicia dasycarpa) and Paraggio medic (Medicago truncatula v. Paraggio), were established using various techniques (Table 1) on a medium textured soil (Table 2) in Stellenbosch, at the Nietvoorbij campus of the ARC Infruitec-Nietvoorbij. Each treatment (establishment technique) was replicated three times in a randomised block design. The percentage cover crop seed that germinated was determined the first week of June (seven weeks after the seeding date) by counting the number of plants per 0,5 m and expressing this figure as a percentage of the number of seeds sown per m. The DMP was determined at the end of August by sampling the above-ground fibre per 0,5 m and drying it for 48 hours at 105C, whereafter the dry mass was determined.

Table 1. Establishment techniques applied
Technique
Action
Date
1
Working fibre into soil with disc
Seed bed preparation with disc
Covering of seed with disc
3 March
15 April
15 April
2
Seed bed preparation with disc
Covering of seed with disc
15 April
15 April
3
Working fibre into soil with disc
Seed bed preparation with disc
Covering of seed with spike harrow
3 March
15 April
15 April
4
Seed bed preparation with disc
Covering of seed with spike harrow
15 April
15 April
5
Working fibre into soil with disc harrow
Seed bed preparation with disc harrow
Covering of seed with disc harrow
3 March
15 April
15 April
6
Seed bed preparation with disc harrow
Covering of seed with disc harrow
15 April
15 April

Table 2. Analysis of the 0-300 mm soil layer of the Avalon (medium textured) soil at the ARC Infruitec-Nietvoorbij experimental farm in Stellenbosch (Nietvoorbij campus) where the experiment was conducted
Soil layer
(mm)
P
(mg/kg)
PH
(KCl)
Organic C
(%)
Clay
(%)
0-300
21.8
6.7
0.53
17.06

RESULTS AND DISCUSSION

Rye established well when the rotary harrow or disc harrow was used for soil cultivation, regardless of the seed bed preparation technique (Table 3). The cultivator seemed unable to cover the rye seed sufficiently with soil on this soil type (Treatments 3 and 4), hence the lower germination percentage compared to the treatments where the rotary harrow or disc harrow were used for this purpose. Although the DMP did not differ significantly between treatments, it tended to increase if the previous season’s mulch was worked into the soil six weeks before sowing. This early cultivation probably prevented the development of a nitrogen deficit during the initial growth phase of the cover crop, in that most of the fibre decomposes during this six week period. This additional treatment may also have caused better control of early germinating weeds, with an accompanying decrease in weed competition. Despite the poor germination obtained with a cultivator, the eventual DMP was similar to that obtained with the other two implements. This indicated that in the case of rye, mistakes made during establishment of the cover crop, may to a large extent be rectified by managing the cover crop correctly after sowing (fertilisation at the two to four leaf stage and irrigation). However, the correct establishment technique (ET) may enable the sowing density to be adjusted downwards.

Table 3. The percentage seed that germinated and dry matter production (DMP) of rye, Paraggio medic and vetch
Treatment
Rye
Paraggio medic
Vetch
% germinating
seed
DMP (tons/ha)
% germinating
seed
DMP (tons/ha)
% germinating
seed
DMP (tons/ha)
Technique 11
71 ab2
3.60
43 abc2
1.96 ab2
71
2.11

Technique 2
77 ab
2.82
30 bc
1.42 b
78
2.13

Technique 3
31 b
3.48
55 abc
1.45 b
77
2.47

Technique 4
41 ab
3.22
27 c
1.82 ab
70
2.01

Technique 5
76 a
3.90
73 ab
5.11 a
95
2.56

Technique 6
71 ab
2.21
74 a
2.65 ab
100
2.94

1. See Table 1 for description of Technique.
2. Data followed by various letters differ significantly from each other at the 5% level.

Paraggio medic performed the best where the rotary harrow was used (Table 3). The rotary harrow creates a finer seed bed than the disc harrow. This creates favourable soil conditions for the establishment of Paraggio medic that has relatively small seeds. In contrast to the cultivator, the rotary harrow covers the seeds effectively on this soil type. The species’ DMP was considerably more where the initial tillage was done with the rotary harrow, probably due to better control of early germinating weeds and avoiding a nitrogen negative period after sowing.

The percentage germination for vetch was never less than 70%, regardless of the implement or technique used. However, the best results were once again obtained with the rotary harrow. As in the case of rye, a higher germination percentage did not result in a higher DMP. It appears as though mistakes made during establishment may be rectified with good cover crop management after sowing.

CONCLUSIONS AND RECOMMENDATIONS

Cover crops with small seeds (Paraggio medic) or medium size seeds that are round (vetch) or long (rye), should preferably be established with a rotary harrow on these medium textured soils.

The previous year’s fibre should be worked into the soil about four to six weeks before sowing.

In the case of both rye and Paraggio medic, the establishment technique had an effect on cover crop performance.

Managing the cover crop correctly after sowing, may negate the mistakes made during establishment to a large extent. However, by using the correct ET, sowing density may be reduced.

LITERATURE

FOURIE, J.C. & LOUW, P.J.E., 2002. Die geskiktheid van verskillende dekgewasse vir volhoubare deklaagbewerking in die Olifantsriviervallei en omliggende gebiede. Wynboer (voorgelê vir publikasie).

FOURIE, J.C., LOUW, P.J.E., & AGENBAG, G.A., 2001. Effect of seeding date on the performance of grasses and broadleaf species evaluated for cover crop management in two wine grape regions of South Africa. S. Afr. J. Plant & Soil 18, 118-127.

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