The influence of sowing depth, compaction and fertiliser placement on caucasian, subterranean and white clover grown in pots : A dissertation submitted in partial fulfilment of the requirements for the degree of Bachelor of Agricultural Science with Honours at Lincoln University, New Zealand

Abstract

An experiment to measure the effects of sowing depth and soil compaction on emergence, early growth and development of Caucasian clover (Trifolium ambiguum M. Bieb), subterranean clover (Trifolium subterraneum L.) and white clover (Trifolium repens L.) was sown on 5 April 2002, into a low fertility soil, in a pot experiment at the Lincoln University glasshouse facilities, Canterbury, New Zealand. Five sowing depths 0-mm (surface sown), 20-mm, 40-mm, 60-mm and 80-mm, each with a compaction layer (80-mm below soil surface), or no compaction, were investigated. By 14 August 2002 plants had emerged from the 0-mm, 20-mm and 40-mm sowing depths; no plants had emerged from the 60- and 80-mm sowing depths. The soil compaction had restricted root length in the subterranean clover plants only, by 51-mm. The surface sown seed of all three clover species gave 75% or greater emergence 22 days after sowing. This was due to the friable nature of the and white clovers 39%, 73% and 43%, respectively. The low emergence of the Caucasian clover was due low seed vigour, while white clovers' small seed size (1.2g thousand seed weight, compared with 3.5g and 4.2g for subterranean and Caucasian clovers, respectively) and lack of seed reserves reduced seedling emergence from the 20-mm sowing depth. Plants that grew from the 40-mm sowing depth were considerably smaller: and slower in development because of their delayed emergence, than those from the 0-mm and 20-mm sowing depths. Phyllochron is a measure of the thermal time requirement for the appearance of the number of leaves per plant. White clover phyllochron was calculated to be 91⁰C days and stolon initiation occurred at 374⁰C days. Caucasian clover had a phyllochron of 541⁰ C days and rhizome initiation had not occurred in the 1082⁰C thermal time accumulation (base temperature 4.2⁰C for germination and 1⁰C for subsequent growth) for the experiment. This high phyllochron, or slow rate of leaf appearance in the Caucasian clover may be due to another limiting factor, possibly nutrient deficiency. A fertiliser placement experiment was established to investigate the effect of fertiliser on root growth and development. A pot trial using a low fertility, sieved soil at the Lincoln University glasshouse facilities had three placements of fertiliser, either placed 20-mm below the seed, with the seed or broadcast on to the soil surface. Fertiliser broadcast (above the seed) gave the greatest root dry weights for all three clover species (0.219g plantCaucasian clover, subterranean clover 0.720g plant⁻¹ and white clover 0.321 g plant⁻¹).