Evaluation of Italian Ryegrass Establishment into Kikuyu Pastures

FARMER-INITIATED TECHNOLOGY TRANSFER (FITT) PROGRAMME

Introduction

Kikuyu grows very well in the warmer months but is relatively dormant through the cooler winter months. For this reason, many farmers have started to undersow or broadcast Italian ryegrass into the existing pastures to provide some winter feed. Broadcasting seed and then mulching so the seed is buried in the trash has been shown to be a successful technique of introducing Italian ryegrass. Broadcasting seed without mulching is understood to have unreliable results.

A large research project has been running for three years at Northland Agricultural Research Farm (NARF) in Dargaville. This project compares three pasture systems: a predominately ryegrass-based farmlet, and two kikuyu-based farmlets, one of which is mulched in autumn and one of which relies on stock pressure to maintain control. Italian ryegrass seed is sown during late autumn within both of these kikuyu-based farmlets, either through drilling prior to mulching on the mulched farmlet or broadcasting and grazing on the non-mulched farmlet. This FITT project was initiated to collect information on the success of this sowing of Italian ryegrass with and without mulching within the large scale trial at NARF. This is additional data that would not have been collected otherwise.

Key Aims– What was the Project Trying to Achieve?

Comparing the effectiveness of establishing Italian ryegrass seed in kikuyu pastures with and without mulching.

Key Findings and Recommendations for Farmers

• Italian ryegrass seedling establishment appeared very low during the ‘growthy’ 2011 autumn, however though seedling numbers were low, mulched pastures had 8 times the Italian seedling count of non-mulched pastures
• Mulched pastures had a higher proportion of Italian ryegrass and less kikuyu and other grasses than nonmulched pastures
• Broadcast sowing of Italian ryegrass into kikuyu pastures during a ‘growthy’ autumn without mulching would appear to result in low plant establishment

METHODOLOGY – WHAT WAS DONE IN THE TRIAL?
During June 2011, measurements were taken on six paddocks where Italian ryegrass seed was introduced through drilling seed prior to mulching and anothersix paddocks where seed was broadcast without mulching occurring. Sowing (and mulching) occurred from mid April through to early May 2011. On 14th June measurements taken on each paddock were:

• Seedling counts within 10 randomly placed quadrats (size 50cm by 25 cm)
• Collection and botanical dissection of a pasture sample plucked to a height of 2 cm
• Collection of pasture samples and botanical dissection occurred again on 14th September.

RESULTS
Autumn and early winter pasture growth was very strong within the farmlets. Pasture cover was especially high on the non-mulched farmlet when sampling occurred in mid June with a lot of kikuyu stolon in the base of the pasture.

SEEDLING COUNTS
Overall the number of seedlings counted within the sward was considered very low with an average of 4.7/m2. However, identifying Italian ryegrass seedlings within this competitive sward was difficult and there was a lack of confidence that all seedlings present were counted. The data (Figure 1) does show 8 times the number of seedlings within the mulched pastures than the non-mulched pastures.

Figure 1. Average Italian ryegrass seedling count per square metre where introduced with or without mulching

PASTURE DISSECTIONS
Pasture samples were collected and dissected in June and again during September.
An average of 64% of the sward as Italian ryegrass at the September assessment should be viewed as a
successful establishment within the mulched paddocks (see Figure 2). Even 37% within the non-mulched paddocks is a significant proportion. It is unknown
how much of the Italian ryegrass is a result of this years oversowing. Indications from the seedling counts would suggest that a large proportion of the Italian ryegrass present was carry-over from the previous season, especially within the un-mulched treatment.
The proportion of Italian ryegrass within the sward was significantly higher in the mulched than the non- mulched treatments at both assessment times.

Figure 2. Average Italian ryegrass proportion within the sward where Italian ryegrass was introduced with or without mulching

Mulching reduced the proportion of kikuyu within the sward at the June assessment, however by the
September assessment kikuyu presence was low within both treatments (see Figure 3).

Figure 3. Average kikuyu proportion within the sward where Italian ryegrass was introduced with or without mulching

There was no significant difference between treatments in the presence of perennial ryegrass (see figure 4).

Figure 4. Average perennial ryegrass proportion within the sward where Italian ryegrass was introduced with or without mulching

Mulching significantly reduced the proportion of other grasses within the sward at the September assessment (see Figure 5). The majority of the other grasses present were observed to be Poa spp. These ‘filler’ grasses appear to have taken up space left within the sward due to the seasonal kikuyu dieback, whereas much of this space was likely filled by Italian ryegrass within the mulched treatment.

Figure 5. Average proportion of other grasses within the sward where Italian ryegrass was introduced with or without mulching

CONCLUSIONS
Establishing Italian ryegrass within existing kikuyu based pastures was much more effective when introduced with mulching rather than without mulching.
Overall Italian ryegrass seedling establishment in this ‘growthy’ autumn appeared to be low within both treatments, however introducing Italian ryegrass seed through mulching compared to not mulching showed 8 times the seedling establishment compared to not mulching.
By September, mulched pastures had almost twice the proportion of Italian ryegrass within the sward and half the proportion of other grasses compared to non-mulched pastures.

HOW WILL THE GROUP APPLY THE PROJECT RESULTS TO THEIR AGRI- BUSINESSES?
This information is one component of a large farm systems trial. This information helps complete the picture of the larger trial which will assist farmers in making decisions around regrassing and kikuyu
management. Good information on which to base these decisions is very important for Northland farmers.

Prepared by: Kate Wynn and Chris Boom
Date: 14 November 2011

Download full trial design and results here: