Newer cultivars much improved

Date: 2009-02-01 | Category: News

Changing pasture species or cultivars is a key step in the pasture renewal process, according to a benefit-analysis report.

It was prepared for the Pasture Renewal Charitable Trust (PRCT), formed to help accelerate the rate of pasture renewal on New Zealand farms.

The report, prepared by AgResearch, says changing pasture species or cultivars has potential to change total drymatter production, seasonality of production, feed quality, animal health and ultimately, boost animal productivity from new pasture.

It says taking the decision to renew usually rectifies the factors that led to the decline of the original pasture.  So changes to soil fertility, the soil's physical structure, and the pest and disease cycles can result. 

Utilising new pasture for grazing by a range of stock types, plus hay and silage making, has a unique set of outcomes that impact directly on the size of any productive and economic gains and how long those gains will last.

The report says selecting which pasture species to sow is a major decision to be made after deciding to renew pastures.  The choice made will affect the resulting life span of the pasture and its productivity.

Some cultivars are bred for specific purposes so they are not expected to last as long in pasture compared to perennial species e.g.  chicory and red clover.  The ryegrass continuum (figure 1) shows the range from annual to perennial species and is as an effective tool to help explain how to choose cultivars that best meet the objectives expected from a new pasture. 

Understanding the relationships between cultivar types, best use and expected longevity helps the selection of cultivars that best fits the farmers' expectations, the report says.

Up until the early 1980s, the breeding of other varieties and species concentrated on providing a range of pasture plants that were uniform, consistent and adapted to NZ grazing systems.

Ryegrass cultivars currently dominate the market and are included in the majority of new sowings so the impact of genetic gain is important to consider when selecting cultivars.

Italian ryegrass improvement has been estimated at between 1.2 - 1.5%/year and perennial ryegrass gains at between 0.25 - 0.73%/year, with higher gains now being estimated.

The genetic gain of seasonal yield in annual and perennial ryegrass has also been estimated.

This is a key feature of annual ryegrass and contributes significantly to farmers choosing to use this species.  The greatest gains have been made in the summer and second autumn yields (2.67 and 3.62% respectively) which show increasing longevity is a major benefit of this species.

For perennial ryegrass gains in summer-autumn yield are estimated to be 0.7% which is greater than the annual total improvement.

AgResearch found the genetic gain in NZ white clover cultivars is estimated to have increased forage yield when tested under local grazing conditions.  These gains were 1.5% and 1.2%/year under sheep and cattle grazing respectively.

Gains estimated since the introduction of Plant Variety Rights have been even greater with increases as high as 2.5-4.4% a year.

It is clear farmers select new sires each year to gain in their livestock.  But AgResearch found the adoption of new genetically improved cultivars for pasture renewal has been slow, despite genetic gains in pasture species being in line with those made with livestock.

The genetic gains for pasture species in the past 20 years equate to cultivars producing from 15 and 50% more annual drymatter yield from ryegrass and clover respectively than the older cultivars. 

Evidence to support this increase in drymatter production comes from the NZ Plant Breeders Association trial results for ryegrass from 1991 to 2005.

The two newest ryegrass cultivars released in 2005 had mean yields of 14.05t DM/ha, compared with the 12.55t DM/ha from the control, which was released in the mid-1980s.  A gain of 15% would equate to a yield in the new cultivars of 14.4t DM/ha.

Total potential gains/ha estimated from these figures shows an increase of 57% in animal output.

This is done by applying the average genetic gain in both pasture and animal performance, weighted for potential ryegrass and white clover production in sowings 20 years ago (12.55t and 2.5t DM/ha respectively).

Total production would increase to 14.4t and 5.0t DM/ha for ryegrass and white clover respectively, while animal productivity would increase by 27% and 6% respectively. 

Actual gains on farm may be quite different from this total, depending on the management systems chosen.

Published courtesy of Country-Wide - March 2008. An edited extract from AgResearch's Literature Review.

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