Response of intensively grazed ryegrass dairy past

Authors: M D A Bolland I F Guthridge G Blincow

Publish Date: 2011/03/09

Volume: 90, Issue: 2, Pages: 281-298

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Abstract

Intensively grazed rainfed dairy pastures on the predominantly sandy soils in the high rainfall 800 mm annual average Mediterraneantype climate of southwestern Australia comprise 90 ryegrass annual ryegrass Lolium rigidum Gaud and Italian ryegrass L multiflorum Lam To maximise pasture use for milk production the pastures are rotationally grazed by starting grazing when ryegrass plants have 3 leaves per tiller and fertiliser nitrogen N and sulfur S in the ratio of 3–4 N and 1S need to be applied after each grazing for profitable pasture dry matter DM production In addition farmers usually also apply low levels of phosphorus P and potassium K fertiliser to these pastures after each grazing despite Colwell soil test P usually being well above critical values for pasture production and fertilizer K being only required for clover in the traditional clover Trifolium subterraneum L ryegrass pastures of the region In field experiments undertaken May 2006–June 2010 on intensively grazed ryegrass dairy pastures in the region no significant ryegrass DM responses to applied fertiliser P or K were obtained regardless of level or method of P or K application When no P was applied soil test P declined gradually by between 44 and 71 mg/kg per year and remained above the critical value for the soils at 2 sites but declined below the critical value for soil at a third site Critical soil test P is located near the maximum yield plateau in the flat part of the relationship between yield and soil test P particularly when as appropriate for dairy production the critical value is for 95 of the maximum pasture DM yield Consequently when no P is applied and soil test P decreases significant pasture DM yield decreases will only occur when soil test P approaches the steeper part of the relationship which can take some time In addition as occurs on farms faeces deposited by cows while grazing supplied P to pasture even when no fertiliser P was applied Soil K testing proved unreliable for indicating the need for fertiliser K applications to pasture in the next growing season because many soil samples collected within and between urine patches contained elevated levels of K deposited by cows while grazing We conclude fertiliser P should only be applied to intensively grazed ryegrass dairy pastures when soil testing indicates it is required Further research is required to assess if plant K testing is an alternative but urine patches may also pose a problem for plant testingThe experiments were undertaken on properties of the following farmers who provided enthusiastic support and helped in many ways Miles and Dionne Mottershead Grant Peter and Sue Evans and Victor Denise and Kath Rodwell Technical assistance was provided by Peter Needs Funds were provided by the Government of Western Australia and Dairy Australia Greener Pastures 1 project DAW11011 We are grateful for comments and suggestions of anonymous referees which helped us improve the paper

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