Clovers are an important part of the rotation for many Arable farmers, particularly in mid and north Canterbury. White clover is the most important clover by area with approximately 5000ha grown annually. Generally, the number of flowers produced per meter square drives the seed yield of clovers when pollination is not limiting. Many clover species require insects, usually honey or bumble bees, for pollination to be successful. Weed control is important in clover seed production to ensure market access in international markets, low dressing losses and low competition towards the crop.
Irrigation of white clover
White clover (
Trifolium repens) is an important forage species in New Zealand because it fixes nitrogen, is high in feed quality and improves forage intake of animals. It is usually sown in a pasture mix at 2-3 kg/ha and can be found in most NZ pastures, in well managed pastures it can make up to 20-30% of pasture content. White clover crop seed yields in NZ range between 100 and 1000 kg/ha with an average of approximately 650 kg/ha. White clover seed yield is primarily driven by flower number, which in turn is affected by the canopy density and shading of emerging flower heads. Overwatering can cause lush vegetative growth and reduce light to stolons, therefore reducing flower production and hence seed yield. Other studies have shown the effect of irrigation timing can be used to manipulate white clover canopy growth prior to flowering and at seed fill during flowering and therefore seed yield. Studies have shown that moisture stressing white clover at flowering can increase seed yield and that the optimum potential soil moisture deficit (PSMD) on heavy soils is approximately 350-450 mm. It has also been found that seed yield is closely related to flower number. The objective of this trial was to investigate how irrigation timing and rates from the onset of flowering effects white clover seed yield and to determine the optimum PSMD on lighter soil types, which is more representative of Canterbury.
FAR is interested in seed production of all possible commercial crops which could benefit Arable farmers in NZ. One possible crop for the future in Subterranean clover where FAR trials have shown it is possible to produce in excess of 1000 kg/ha of harvestable seed. Work is now required to investigate methods of removing seed from burs to make this a commercial crop.
Phenoxy herbicides for weed control in white clover
In New Zealand (NZ) growers of white clover for seed production face decisions on herbicide products, rates and timings to control a number of challenging weeds. It is well known that an essential element to achieving high white clover seed yields is to minimize (i) in-field competition and (ii) the seed cleaning losses by achieving high level of field hygiene. The roles of base herbicides such as flumetsulam and/or imazethapyr are quite well understood. Control of some difficult weeds such as thistles, ( Carduus, Cirsium, Sonchus spp.), hawkweeds (Crepis spp.) and groundsels (Senecio spp.) have been a longtime challenge. Herbicide options include the phenoxy herbicides, of which the range commonly used in NZ are an MCPB/MCPA mix, various forms of 2,4-D: 2,4-DB, 2,4-D Amine in SC and WG forms, and 2,4-D Ester. These products have different levels of efficacy and selectivity towards the clover crop. The MCPB/MCPA mix has high crop selectivity but is effective on a narrower range of target weeds and they need to be at early growth stage, whereas at the opposite end 2,4-D Ester has greater weed efficacy but causes a high level of crop growth damage.
To assist growers in the decision processes, and to demonstrate these herbicides to visitors to the 2013 IHSG workshop a trial was established at Creeside Farm near Methven to demonstrate the effect of phenoxy herbicide products and rates, used in conjunction with a proprietary herbicide Jaguar® (bromoxynil + diflufenican), applied at two timings July 22 and August 22.
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FAR continues to investigate the application of Plant Growth Regulators (PGR) to white clover. In white clover initiation of flower numbers does not limit seed yield of white clover where over 2000 flowers per m2 are initiated during spring. Shading of newly emerging flowers leads to flower abortion and is the main factor limiting seed yield for New Zealand seed producers. Thus, FAR is investigating methods to either reduce leaf size (often associated with fertility and soil water status), to ensure more light reaches the stolons, reduce internode length and thus encourage more leaves flowers to emerge. This work involves methods including topping, cultivation, inter-row spraying, irrigation and PGR applications.
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