Investigation into the mechanisms causing lime responses in a grass/clover pasture on a clay loam soil

Abstract

A mowing trial was conducted on the Mangatea clay loam (a yellow‐grey earth or Umbric Dystrochrept fine hallositic mesic) to examine the mechanisms causing lime responses in a grass/ clover pasture. The trial site was located on a sheep and beef farm 8 km south of Te Kuiti, New Zealand. The site generally had cool winters and warm moist summers, with an annual rainfall of about 1400 mm. The treatments consisted of 3 lime rates (0, 5000, 10 000 kg ha⁻¹) in the absence of P and 6 lime rates (0, 1250, 2500, 5000, 7500, 10 000 kg ha⁻¹) in the presence of P (50 kg P ha⁻¹ yr⁻¹), all in the presence of sodium molybdate (Mo), and an additional treatment where P was applied in the absence of lime and Mo. Lime increased grass yield but decreased clover yield for the first 2 years after application. In Years 3 and 4, the responsiveness of the grass decreased and that of clover increased. Lime increased net N mineralisation by up to 58 kg ha⁻¹, resulting in increased grass growth. Plant P uptake in both grass and clover also increased when lime was applied. However, yield responses were only seen in summer in clover when plant P concentrations in clover were less than 3.0 mg g⁻¹. The lime‐induced increase in Mo availability would contribute to lime responses if basal Mo was not applied. Subsoil Al toxicity, particularly in summer, was limiting growth in some parts of the trial. However, there was no evidence that Mn toxicity was limiting yield, nor of any lime‐induced trace nutrient deficiencies. Results from the application of P and Mo indicate that there was at least a 6‐month delay in the transfer of N from clover to grass, with about 30% of the extra clover N uptake in Year 1 being transferred to extra N uptake in grass in Year 2.

Keywords:

• aluminium
• clover
• fertiliser
• grass
• lime
• mechanism
• molybdenum
• nitrogen transfer
• phosphate
• response
• soil moisture