Agronomic studies in red clover seed production: A dissertation submitted in partial fulfilment of the requirement for the Degree of Bachelor of Agricultural Science with Honours at Lincoln University New Zealand

Abstract

The effects of time of closing and level of nitrogen on final seed yield, flowering pattern, seed yield components and dry matter were investigated in a Grasslands Colenso red clover (Trifolium pratense L.) field experiment. Closing date treatments included 15th of October 1996 (C₁), 7th of November (C₂), 1996, 21st of November, 1996 (C₃) and the 13th of December, 1996 (C₄). In the three latest closing date treatments the effect of two rates of nitrogen were also investigated. Rates included no nitrogen (N₁) and 20kgN/ha (N₂) applied as urea. The experiment design was a randomised block design with four replicates. Nitrogen had no effect on any of the components measured, probably due to the high soil fertility status of the second year stand. At 317 and 300kg/ha the bulk seed yields of C₃ and C₄, respectively were higher than the two earliest closing treatments C₁ (248kg/ha) and C₂ (220kg/ha). Yield component measurements failed to explain these differences , but they did show that the low seed yield in C₁ was associated with a slight decrease in the number of seeds per inflorescence. Comparison of the experimental yield components with those of a much higher yielding commercial crop nearby suggested that the low seed yields were associated with poor pollination resulting from a low nectar flow, inclement weather, an absence of pollinators or some combination of these factors. Thermal time alone did not predict when peak numbers of inflorescence production occurs. Later closing resulted in a delay in inflorescence appearance producing a distinct period of peak numbers of inflorescences. The earliest closing treatment accumulated a large amount of thermal time due to being closed for the longest duration in relation to the photoperiod stimulus. The stimulus for flower initiation in red clover was determined to be not a particular day but the accumulation of several factors and was an ongoing process. This can explain why flower production occurred at an earlier date in progressively earlier closed crops. This allowed these treatments to produce more advanced development of both stems and inflorescences. A seven point scale was drawn up to describe and quantify inflorescence development. Variation in the rate of inflorescence development from the visible green hairs stage (stage 1) was influenced by both variations in accumulated thermal time and closing date. The increased rate of development exhibited by the earlier closing date and the first fortnightly interval were associated with varying canopy microclimate and accumulated thermal time. The results confirmed that after flower initiation, inflorescence development is driven purely by temperature. An separate experiment within the same experimental area of Colenso examined the effects of applying MCPA to the maturing crop, a practice commonly used commercially to restrict late vegetative growth. MCPA at 0, 1, 2 and 4 litre/ha was applied on the 19th of March and seed was hand harvested on the 9th of April 1997. Two independent germination tests performed on the seed samples, one at Lincoln University and one by the MAF seed testing station in Palmerston North showed no significant differences between seed quality and the rate of MCPA applied. Normal seedlings and abnormal seedlings for both tests ranged from (60 - 70%) and ( 4 - 10% ), respectively. This result is possibly due to the seed having reached physiological maturity before the application of the herbicide. Some differences in the results produced by the two tests were attributed to differences in technical skills and laboratory equipment.