Cheyenne Nicholson

Recent trends of land use in New Zealand has created pressure to finish a larger number of sheep and beef animals on hill country farms, largely due to the more productive finishing land being converted to dairy production or dairy support. It means research into hill country and improving hill land is becoming increasingly important.

A selection of papers focused on hill country research were presented at the 2017 Grassland Association conference.

Phosphate fertiliser application and white clover cultivar introduction for hill pasture improvement

The basis for achieving pasture productivity gains in New Zealand hill land lies in the ecological concepts described by Sears and levy in 1960 and 1970 respectively. Nitrogen (N) is the nutrient most strongly limiting pasture growth in hill pastures followed by phosphorus (P).

The classical pasture improvement sequence addresses the N limitation by first reducing the soil P deficiency to create an environment favourable to legume growth. This increase in clover in turn stimulated biological nitrogen fixation and nutrient cycling processes.

White clover cultivars bred specifically for NZ hill environments have been around since the 1990s but while there is a lot of agronomic information available from small-plot studies with white clover cultivars in hill country, the impacts of cultivar introduction on animal production aren’t known. With a range of factors that influence hill land productivity it is un-wise to assume results seen in small, simple plot experiments will translate to higher animal production in self-contained grazing systems.

A research project that originally began in the mid-1980s and presented at the 2017 Grassland conference looked to compare the animal production response to P fertiliser application with the introduction of white clover cultivars in hill country.

The how

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 introduce in 1986) Huia and Tahora.

Fertiliser rates: 0,8.5, 22.5 and 26.5 kg/ha/year of citrate – soluble P.

Grazing management “wasn’t terribly sophisticated” and 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 were clear. Both P fertiliser addition and white clover cultivar introduction significantly increase 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.

Practical implications: Managing for improved productivity

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 liveweight gain/ha compared with unfertilised.

“The established recommendation of viewing 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.”

Sediment and nutrient losses under winter cropping on hill country soils

Aerial Spraying and surface seeding of winter crops in uncultivable hill country is being rapidly adopted as a method of increasing winter feed supply and as a precursor to regrassing. There is little research on the sediment and nutrient losses that may result from this practise. Given the current focus on the environmental aspects of farming, this paper looked to quantify sediment and nutrient losses from hill country cropping

The study was carried out at Massey University’s Tuapaka Agricultural Experiment Station. Two small sub-catchments were selected for the study and features sloped ranging from 0-28 degrees and contrasting soil types. Crop type: swedes.

Soil damage caused by the winter grazing of the swedes generated sediment losses that were 5.5 times greater on the imperfectly drained soil than the well-drained soil. Surface run-off over three months resulted in losses of 1.1 tonnes/ha of sediment, 0.85kg of P and 5.4kg of N/ha from the poorly drained soil.

The key risk period contributed between 99-99% of the total annual sediment and total N and P losses compared to pasture and crop establishment phase. A comparison with two other sediment and nutrient loss studies on the same farm suggested the losses associated with winter cropping in the landscape may be extreme. It highlighted the need for targeted mitigation strategies and strategic grazing management to reduce soil and nutrient losses to minimise the impacts on waterways of winter grazing of hill country crops. Further research is required to assess the practicality of different mitigation options.