PRODUCTIVITY OF KIKUYU–RYEGRASS PASTURE AS AFFECTED BY METHOD OF CULTIVATION.

In the south-eastern seaboard area pastures for dairying are mainly based on ryegrass-kikuyu as the main fodder. The pastures are established or reinforced with various soil preparation implements, which may cause little to various degrees of soil disturbance. The popular method consists of ryegrass over-sown into kikuyu in a minimum-till pasture system. This system has many benefits, such as increased production and forage quality during the period when the kikuyu is dormant. However, grazing management after ryegrass emergence is key to the success in maintaining the ryegrass in the kikuyu-based pasture. One aspect is competition-induced stress by the kikuyu pasture which may be significant on the over-sown seedlings and subsequently affects the overall production. Cultivation or other methods of pasture disturbance may reduce this problem to some extent by decreasing the competition from the resident pasture base, giving the over-sown pasture time to establish. The most common system used to sow ryegrass in autumn is using a mulcher and a minimum-till seed drill. Other methods to decrease competition from the pasture base may include the application of herbicides to the resident pasture before sowing or after conventional tillage with various implements causing severe soil disturbance and inversion. 

The effect of these cultivation practices or methods to over-sow ryegrass into kikuyu on production potential of the pasture is not known. They may have substantial influences on the chemical, physical and biological processes within soil, and may therefore also influence pasture productivity. The aim of this study, therefore, was to assess the impact of cultivation associated with over-sowing ryegrass into a kikuyu pasture, using varying degrees of disturbance, on pasture productivity and botanical composition.

In the study, five tillage treatments were assessed, namely kikuyu over-sown with ryegrass using a minimum till planter, eradication of kikuyu with herbicide and ryegrass sown with a minimum-till planter, shallow (less than 150 mm) and deep (more than 150 mm) disturbance with a rotavator or conventional tillage, respectively, and a control. The autumn, spring, summer and annual productions of treatments with the least soil disturbance were the highest . Shallow or deep tillage resulted in intermediate annual productions and the lowest was recorded for the herbicide treatment. Differences in production caused by different tillage methods were significant. The methods also changed the botanical composition. The most viable option to manage cultivated pastures whilst maximising pasture productivity and quality was by mulching the existing kikuyu base and over-sowing it with ryegrass using a minimum-till seed drill. 

Reference: 

P.A. Swanepoel, P.R. Botha, H.A. Snyman & C.C. du Preez, 2014. Impact of cultivation method on productivity and botanical composition of a kikuyu–ryegrass pasture, African Journal of Range & Forage Science, 31:3, 215-220, DOI: 10.2989/10220119.2014.903999