Establishment of white clover seed crop under spring barley

A series of trials was carried out from 1984/85 to 1986/87 with two main objectives: to establish an adequate number of white clover plants under barley and to investigate the mechanism of competition between barley and white clover. White clover cultivar 'Grassland Huia' was undersown in 30 cm rows with barley cultivar 'Triumph' in all the trials. The combination of an adequate number of white clover plants with even distribution within rows was also investigated. Barley populations and row geometries were assessed in dryland trials during 1984/85 and 1985/86 and in an irrigated trial during 1985/86. No white clover plants survived under barley during 1984/85 due to severe drought in December and January and grain yield of about 3.5 t ha⁻¹ was not affected by the treatments. White clover plants surviving after barley harvest during 1985/86 were not affected by barley geometries in the dryland trial. However, an increase in barley population from 70 to 210 plants m⁻² reduced the number of surviving plants from 346 to 176m⁻². In the irrigated trial a significant interaction between barley population and row geometries showed that increasing barley population to 256 plants m⁻² reduced the number of white clover plants to 32 m⁻² under 15 cm geometry compared with more than 350 plants m⁻² established under lower barley populations or 10/20 cm and 20/40 cm row geometries. Changing barley geometry from 15 cm to 10/20 cm rows did not affect barley grain yield, in both dryland and irrigated trials. However, barley in the 20/40 cm geometry which was used only in the irrigated trial had 16% lower yield compared with 5.4 t ha⁻¹ under the 15 cm row geometry. Increasing barley population increased grain yield in both dryland and irrigated trials during 1985/86. During 1986/87 barley geometries of 15 cm, 10/20 cm and 20/40 cm rows were investigated with or without irrigation and with white clover undersown parallel to or at right angles to barley rows. Irrigation did not improve white clover survival, compared with the dryland crop. However, changing clover sowing direction from parallel drilling to cross drilling increased the number of white clover plants from 25 to 46 plants m⁻². An adequate number (56) of white clover plants survived under the 20/40 cm geometry compared with 19 and 30 plants m⁻² under the 15 and 10/20 cm row geometries respectively. Increase in light transmission to white clover increased its individual plant weight under irrigation (r²=0.804), with little effect under the dryland crop (r²=0.347). Irrigation increased grain yield in barley from 6.4 to 8.0 t ha⁻¹ compared with the dryland crop. Grain yield in barley was similar in the 15 and 10/20 cm row geometries; however, barley yield with the 20/40 cm geometry was 12% less than that under the 15 cm row geometry. A technique was successfully adopted to separate roots and shoots of white clover and barley under field conditions. During 1985/86 irrigation was used in the whole trial whereas during 1986/87 irrigated barley was compared with the dryland crop. Many white clover plants survived (>500 m⁻²) after barley harvest with no differences between treatments during 1985/86. However, white clover dry matter was less in the treatments where shoots were competing than in those where roots were competing. During 1986/87, no white clover plants survived under full competition, whereas only 41 plants m⁻² survived under root competition compared with 117 plants m⁻² under shoot competition in the dryland treatment. However, under irrigation, more than 100 plants m⁻² survived in all the competition treatments except full competition (53 plants m⁻²). White clover dry matter was similar under root and shoot competition in the dryland crop. With irrigation white clover under root competition had 12 times higher dry matter than that under shoot competition. An adequate number of white clover plants can be established along with a high barley yield of about 7 t h⁻¹ if the 20/40 cm barley row geometry is used. The competition for soil moisture was a crucial factor in affecting white clover survival in the dryland crop and competition for light was an important factor to affect white clover dry matter, especially when adequate moisture was present in the soil. A technique was developed to separate roots and shoots of competing species under field conditions. An adequate distribution in white clover sown in 30 cm rows was achieved with 50 plants m⁻², surviving 4 to 6 weeks after barley harvest.