Die produksiepotensiaal van oorgesaaide kikoejoeweiding in die gematigde kusgebied van die Suid-Kaap

English: The aim of this investigation was to quantify the spring-, summer-, autumn and annual DMproduction, botanical composition, nutritional value and milk production potential of kikuyu that is over-sown with annual ryegrass, mixtures of perennial white- and red clover or a mixture of perennial ryegrass and white and red clover, within a sustainable management system. Guidelines around the cultivation practices of these over-sowing techniques were determined. The investigation was executed on the Outeniqua Experimental farm near George in the Western- Cape. Three separate pastures under permanent irrigation over nine hectares during three years were compared in a pasture system study. The experimental design was a randomized complete block design with three treatments being repeated in eight blocks. Perennial white clover (Trifolium repens) cultivars (Haifa and Waverley) and perennial red clovers (Trifolium pratense) cultivars (Kenland and Cherokee), annual westerwold ryegrass (Lolium multiflorum: cultivar Energa) and perennial ryegrasses (Lolium perenne: cultivars Yatsyn and Dobson) were over-sown onto existing kikuyu pasture by making use of three implements, namely a Rotovator, Mulcher and a Land roller. The botanical composition (grass-, clover- and herb content), nutritional value (IVOMD-, TDN-, ME-, CP-, NDF-, ADF-, Ca-, P-content) and DM-content of the different pastures were determined on a monthly basis. The Ellinbank rising plate pasture meter was used to determine the DM-production, DM-production rate and the DM-intake of the pastures. A put-and-take system of grazing, using 36 mid-lactation Jersey cows in three groups (12 per group) for each season (90 days), was implemented. The cows received new strips of pasture after each milking. Cows were moved every second day to a new sub-camp and were absent from any sub-camp for a period of 30 days. Concentrate which contained at leat 120 g crude protein kg-1 DM and 12.5 MJ ME kg1 DM was fed at 4 kg cow' day" to all cows. The milk production and the number of cows kept were recorded and milk composition (butterfat-, protein- and milk solids content) was determined monthly. The mass and the condition score of the test cows were determined at the beginning and end of each test period. The DM-production rate (kg DM ha-1 day') of the pure kikuyu pasture was low during spring (33.9 kg DM ha:' day1) and high during the summer (67 kg DM ha' day") and autumn (71.6 kg DM ha' day'). The DM-production potential of kikuyu was not influenced during summer and autumn by over-sowing it with annual ryegrasses during May. When kikuyu was over-sown with clover, the DMproduction potential was reduced by 17% to 46% during the summer and autumn respectively. Kikuyu that was over-sown with ryegrass, reached a higher annual grazing capacity (8.03 to 9.03 cows ha") compared to that of kikuyu which was over-sown with clover (5.27 to 5.78 cows ha"). The clover component of a kikuyu pasture that was over-sown with clover, remained above 40% for longer than two years. In this instance the clover component was also more sustainable than in the perennial ryegrass clover pasture, where .itwas found that the clover component declined below the 30% level during the first production year. In comparison with ryegrass- and clover pasture, the nutritional value of pure kikuyu is less favourable for optimal milk production. The IVOMD, TDN-, ME- and RP-content of the ryegrass dominant kikuyu pasture was higher and the NDF- and ADF-content lower than that of the pure kikuyu pasture. The IVOMD, TDN-, ME- and RP-content of the clover dominant kikuyu pasture was higher and the NDF- and ADF-content lower than both the ryegrass-kikuyu pasture and pure kikuyu pasture. As the kikuyu component of the kikuyu-clover pasture increased, the IVOMD, TDN-, ME-, RP-content decreased and the NDF- and ADF- content increased. Clover pastures during the first production year had a high ME-content (on average 11.09 MJ kg-1 DM) that meets the energy requirements of a dairy cow. The ME-content of the second production year clover pastures (average 9.86 MJ kg-1 DM) was lower than 10 MJ kg-1 DM when the kikuyu content reached a level more than 50%. The Ca-content of the clover dominant pastures (average 1.03%) was higher than that of the grass dominant pastures (average 0.36%). The P-content of the different pastures differed very little (0.40% to 0.54%) and should meet the requirements of ruminants without any seasonal supplementation. A Ca:P-imbalance (average 0.74:1) occurred in grass pastures, which is lower than the ratio that is normally needed for optimal milk production (1.6: 1). In contrast to this the clover pastures maintained a favourable Ca:P-ratio (average 1.98: 1). The annual milk production from kikuyu pasture was 13.8 kg cow-1 day", ryegrass pasture average 15.5 kg cow-1 day", first production year clover pastures average 16.6 kg cow-1 day", second production year clover pastures average 17.0 kg cow-1 day" and first production year perennial ryegrass clover pastures 18.1 kg cow" day", The milk production per cow reduced as the kikuyu component of the pastures increased. The average annual grazing capacity for kikuyu, ryegrass-, first production year clover-, second production year clover pastures and second production year perennial clover pastures was 6.72,8.53,5.57 and 4.80 cows ha" respectively. The total annual milk and milk solids production per hectare from kikuyu were 21 377 and 1 751 kg ha", ryegrass pastures average 32179 and 2 610 kg ha", first production year clover pastures average 30 277 and 2452 kg ha", second production year clover pastures average 23 454 and 1 815 kg na' and first production year perennial ryegrass-clover pastures 29 298 and 2 266 kg ha" respectively. The lower grazing capacity of the clover pasture, combined with the high milk production per cow, resulted in similar milk production per hectare from the clover- and ryegrass pastures. The grazing capacity of the kikuyu-ryegrass pasture during the autumn (10.8 cows ha") was higher than that during the summer (9.05 cows ha'), but the milk production per cow during the autumn (12.3 kg cow' day ') was lower than that during the summer (20.3 kg cow1 daq"). This resulted in a lower milk production per hectare during the autumn (11 294 kg ha") compared to that of the summer (15780 kg ha"), The lower milk production (4486 kg ha") from the kikuyu during autumn in comparison to that of the summer, indicates the inherent nutritional shortages of kikuyu, which prevents that high milk production can be maintained from kikuyu pastures. The milk production from the over-sown clover pastures per hectare was the highest during the summer (9 194 to 13027 kg ha"), followed by that during the spring (7 370 to 10007 kg ha"), autumn (6 156 to 7 359 kg ha") and winter (3 990 to 4 222 kg ha:'). Milk production from the clover pasture was virtually the same as that from the ryegrass pastures during the spring (8 133 to 11 332 kg ha-1) and that from kikuyu pastures during the summer (9 688 kg ha-1). During autumn the milk production from the ryegrass- (9040 to 11 294 kg ha-1) and pure kikuyu pastures (8 930 kg ha-1) was higher than that of the clover pastures (6 156 kg ha-1). Pasture costs can be halved if kikuyu is over-sown with clover. The pasture costs and direct variable costs per kg milk produced from kikuyu was respectively R0.23 and R0.98 and it can be lowered if it is over-sown with ryegrasses (R0.21 and R0.87) or clovers (R0.10 and R0.71). The net cumulative surplus over two years from the ryegrass (R60 984) and clover pastures (R58 240) was similar and somewhat higher than that from the kikuyu pasture (R37 453). It is economically justified to include both ryegrasses and clovers in production systems. The over-sowing of kikuyu with ryegrass increased the grazing capacity and lowered the unit cost of milk produced. The oversowing of kikuyu with clover lowered the unit cost of grazing and the cost of milk produced. This reduces the risk of a dairy cow enterprise. From a fodder flow planning viewpoint it is recommended that ryegrass and clover pasture should be included in a dairy cow production system to lower the cost and the risk of a dairy production system and improve its economic viability. Kikuyu can be successfully over-sown during May with annual ryegrasses or perennial white- and red clovers by respectively making use of the Mulcher and Rotovator planting method.