Radiation Use Efficiency in Dual Winter Cereal–Forage Production Systems

Received for publication January 19, 2007. Winter cereal production systems in the northern USA are inefficient with respect to the capture of photosynthetically active radiation (PAR) during the year. Our objectives were to determine radiation use efficiency (RUE) in winter wheat (Triticum aestivum L.) and triticale (x Triticosecale Wittmack) at low (67–125 plants m^–2), medium (116–170 plants m^– 2), and high (205–332 plants m^–2) plant densities and RUE of interseeded red clover (Trifolium pratense L.) during two growth periods after cereal harvest. During the linear phase of cereal growth (GS 30–80), RUE averaged across plant density was 3.50 g MJ–1 for wheat and 3.21 for triticale in 2004 and 3.37 for wheat in 2006. In 2006, triticale RUE was similar at the low and medium plant density (3.28 g MJ^–1) but lower at the high plant density (2.84 g MJ^–1). Red clover RUE following wheat and triticale differed by growth period and exhibited varying levels of plant density dependence within growth period. Following wheat at the high plant density, RUE ranged from 1.40 to 1.97 g MJ^–1 across years and growth periods. Following cereal harvest in mid-July until early October, red clover interseeded in wheat intercepted on average 65% (2004) and 35% (2006) of incident PAR. The wheat–red clover system was more robust than triticale–red clover for grain RUE and intercepting PAR after cereal harvest.