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Boosting Hill Country Pastures

As more sheep and beef are being finished on hill country today, it’s become more vital to improve hill country pastures to get better results.

Better feed quality, and an extended seasonal pattern of feed supply from pasture, are two of the critical requirements to achieve the additional 10kg meat sold per breeding ewe (or equivalent) considered necessary for hill farm viability over the next 15 years (Fennessy et al. 2016).

Nitrogen (N) is the nutrient most strongly limiting pasture growth in hill pastures, followed usually by phosphorus (P).

A recent scientific study looked at the strengths of phosphate fertiliser and clover cultivars in relation to hill pasture improvement. The paper, ‘The relative strengths of phosphate fertiliser applications and white clover cultivar introduction for hill pasture improvement’, was presented at the 2017 Grassland Association conference.

The study included combinations of four P fertiliser rates and three pasture types with different white clover germplasms were compared in self-contained, replicated farmlets grazed by sheep over four years. The trial was done on the low-fertility no improvement hill land at Ballantrae Hill Country Research station.

White clover germplasms: The resident clover (first introduced in 1986) Huia and Tahora. Fertiliser rates: 0,8.5, 22.5 and 26.5kg/ha/ year of citric – soluble P.

Grazing management ran on a two-paddock, two-week on two week off system. Pasture covers were monitored on all plots and stocking rate adjusted to utilise pasture growth in a give and take type system.

The results of this experiment showed both P fertiliser addition and white clover cultivar introduction significantly increased animal production (measured as liveweight gain/ha/year). There were no significant interactions between fertiliser inputs and pasture type for any of the variables.

Fertiliser increased white clover herbage accumulate (HA) three to four-fold compared with the control treatment increasing total sward HA by 50%. The introduction of Tahora white clover increased white clover and total sward HA and nitrogen fixation compared with the resident and Huia-sown swards.

Sheep liveweight gain was greater in all systems fertilised with P and in systems sown with Tahora. A mean 12% improvement in animal performance from the introduction of a persistent adapted clover cultivar, at low initial cost, appears to offer an economically viable strategy for improving hill land production.

The three fertilised treatments produced an average 80% greater live weight gain/ha compared with unfertilised.

The improved availability of soil N resulting from greater clover growth and higher N fixation stimulated the growth of more productive grass species such as perennial ryegrass: compared with low fertility-tolerant grasses such as browntop, perennial ryegrass has the potential to grow more herbage on an annual basis and is more productive in winter when low pasture growth rates commonly limit stocking rates on hill swards.

An extra 300kg of white clover drymatter (DM)/ha/year was grown in the Tahora-sown sward compared with the resident, but a further 1000kg DM/ha/year (approximately) came from other species present.

When P fertiliser was applied, N fixation was 2.5-3.2 times greater than where no P fertiliser was applied.

Exclosure cage measurements revealed a strong effect of fertiliser (P<0.001) driven by 45% higher total annual pasture HA in the treatments where P fertiliser was applied compared to the control treatment (mean of 10,530kg DM/ha for the three fertiliser inputs versus 7275kg Dm/ha for control). The results of this experiment showed both P fertiliser application and white clover cultivar introduction significantly increased animal production.

The statistical and absolute effect of fertiliser was much stronger and larger than the effect of white clover cultivar introduction: over four years, fertiliser application increased animal production by an average of 80% compared to the control (unfertilised) treatment, whereas the difference between the best clover cultivar (Tahora) and the pastures based on the resident clover ecotype was only 12%.

The P fertiliser effect was the outcome of a large increase in total white clover HA, increased N fixation, and an increase in total HA of nearly 50%.

Because stock numbers allocated to each replicate of fertiliser x pasture treatment were adjusted fortnightly according to the amount of pasture available for grazing, higher stocking rates were achieved on the fertilised pastures. This was the major driver of increased animal production.

The recommendation of the study was that cultivar introduction as a compliment to fertiliser use, not as a replacement, remains valid and should be considered in any management decision concerning improvement strategies for hill land.

Seed and Feed
Now that the scientific insight is understood, a solution needs to be developed. Fertco have therefore developed a new product to allow farmers to tap into this production and profit benefit, SS8 combines seed-safe Dical 8 and Tahora white clover seed.

Fertco’s preferred form of Phosphate for over 20 years has been Dicalcic Phospate (or reverted super) and particularly our proprietary product Dical 8. One of the reasons for this preference (other reasons will be covered in future articles) is because it is “seed safe”.

This phrase “seed safe” refers to the fact that Dical 8 is close to pH neutral, where other products such as superphosphate are highly acid, pH 1. It is of course the acid in superphosphate that burns seed and therefore renders it not suitable in a lot of cases to be blended with seed.

Appling seed and fertilsier concurrently of coarse makes sense as there are application savings to be made and 400kg per ha, SS8 suppies 32kg of the above scientific paper points out the positive returns.

Designed for a spread rate of 400kg per ha 32 kg of phosphate, 28 of sulphur, 104 of calcium and 3kg of seed is applied. At a cost of $215 per ha plus application.

* Extracts from ‘The relative strengths of phosphate fertiliser application and white clover cultivar introduction for hill pasture improvement’, D.F. Champan, A.D. Mackay, B.P. Devantier, D.A. Costall and P.J. Budding.

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