Effects of lime, phosphorus and sulphur on the establishment of Hairy Canary and Tagasaste on an acid high country soil.

Legumes play a critical role in New Zealand high country farming systems as the sole provider of nitrogen (N) to the pasture sward through biological nitrogen fixation. N also increases the quantity and quality of pastures increasing animal performance, and overall farm productivity and profitability. However, high country soils are commonly acidic, resulting in high concentrations of exchangeable soil aluminium (Al), low soil fertility and moisture stress. Traditional legumes commonly grown in New Zealand high country fail to successfully establish and persist. Alternative legume species that are adapted to acidic soils with low levels of phosphorus (P) are required. Literature on alternative legumes and their soil fertility requirements at establishment is scarce or non-existent. Two woody perennial legume species, tagasaste (Chamaecytisus palmensis) and Hairy Canary (Dorycnium hirsutum) were investigated in a pot trial for 32 weeks at Lincoln University. Plants were established and grown in an acidic high country soil collected from Armidale station, Central Otago. The initial establishment period was under controlled external conditions, before pots were moved into the glasshouse in mid-April. The trial was a fully replicated complete factorial design of two species and 22 treatments. Lime (100% CaCO₃) was applied at four rates (0, 2, 4 and 8 t lime/ha) and P at four rates (0, 50, 150 and 500 P/kg). Sulphur (S) was applied to most treatments at 120 kg S/ha (Gypsum) with a complete ‘optimum’ treatment and a zero S control treatment also included. Plants were harvested five times during the experiment, twice in autumn and three times in winter. Shoot and root yields and lengths were measured and root nodule scores determined. Winter shoot herbage was analysed for macro and micronutrient concentrations. Soils were analysed for pH, P and S contents at the completion of the experiment. Hairy canary was the highest yielding species (4.07 g DM/pot at a soil pH of 5.4), however, for the first two harvests tagasaste grew faster than hairy canary. Total shoot yield for both species ranged from 2.32 to 4.32 g DM/pot. Lime substantially increased the yields of both species to a maximum point, beyond which yields declined with further lime additions. Lime addition significantly increased (P < 0.05) the mean root yield of both legume species. At the most acidic soil pH (pH 4.9) hairy canary was the most productive legume species with a maximum root DM yield of 0.78 g DM/pot, producing 105% greater root mass than tagasaste. The tolerance of these alternative legumes to acidic soils is evident as the greatest root dry matter response occurred at a pH of 5.0 - 5.5 (lime rate 2 – 4 t ha⁻¹). Soil pH was the key driver of yield where increased soil pH reduced soil exchangeable Al levels which in turn increased shoot molybdenum (Mo) and P concentration. Tagasaste was the most responsive legume to phosphorus inputs and experienced the greatest shoot and root growth at the lowest P levels (0 - 50 mg P kg⁻¹). At high lime rates shoot concentrations of Boron (B) and P declined, reducing legume yields. The results show the potential for tagasaste and hairy canary to provide a nitrogen source and high quality feed in acidic conditions typical of the high country. The lack of research in this area indicates the need for these results to be confirmed by field experiments. Applied phosphorus did not increase the DM yield of hairy canary or tagasaste. The initial soil Olsen P was at a ‘medium’ level (17 μg mL⁻¹), hence plant yield response to phosphorus was not significant. Sulphur application caused a significant yield response for both species. Winter and autumn nodulation of tagasaste was significantly increased by lime rate and peaked a pH range of 5.0 – 6.5, which may be directly related to nitrogen fixing ability across a range of soil pH values. The optimum soil pH and Olsen P levels in the soil have been identified for the successful establishment of hairy canary and tagasaste. Their potential growth on acidic high country soils represents valuable and exciting new information. There is a need to confirm the results of this experiment in the field environment under natural climate and grazing conditions, to determine if similar establishment and yield responses would occur in New Zealand high country