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

A mowing trial was conducted on the Mangatea clay loam (a yellow-grey earth or Umbric Dystrochrept fine hallositic mesic) to examine the mechanisms ca using 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 gen erally 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, 1 0 000 kg ha(-1)) in the presence of P (50 kg P ha(-1) yr(-1)), all in the p resence of sodium molybdate (Mo), and an additional treatment where P was a pplied in the absence of lime and Mo. Lime increased grass yield but decrea sed 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. Li me increased net N mineralisation by up to 58 kg ha(-1), resulting in incre ased grass growth. Plant P uptake in both grass and clover also increased w hen 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) Th e lime-induced increase in Mo availability would contribute to lime respons es 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 evi dence that Mn toxicity was limiting yield, nor of any lime-induced trace nu trient 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 gra ss, with about 30% of the extra clover N uptake in Year 1 being transferred to extra N uptake in grass in Year 2.