Productivity, light interception and radiation use efficiency of organic and conventional arable cropping systems

How the productivity of crops in organic arable farming may be sustainably increased remains a key issue. We combined measurements of crop yield, total aboveground biomass (AGB) and light interception over a 4-year crop rotation cycle from 2015 to 2018 in a long-term experiment in Denmark with arable organic and conventional cropping systems. These cropping systems comprise one conventional (CGL) and two organic (OGL and OGC) crop rotations, where CGL and OGL had three spring cereal and one grain legume crop (faba bean) in the rotation, and the faba bean was in OGC replaced with grass-clover. All crop rotations were grown with and without the use of cover crops, and the organic systems were grown with and without the manure application. The light interception was calculated from measurements of spectral reflectance, and this allowed the AGB to be decomposed into accumulated intercepted PAR (AIPAR) and radiation use efficiency (RUE). The conventional cropping system (CGL) had significantly greater AGB, AIPAR and RUE compared with the corresponding organic, grain legume-based system (OGL). AIPAR of the organic grass-clover-based cropping system (OGC) was greater than CGL, although the contrary conclusion was found in AGB and RUE. Across crops, RUE was greatest for cereals and smallest for faba bean and grass-clover. AIPAR was consistently greatest for grass-clover, and both grass-clover and faba bean had smaller variability in AIPAR between years and treatments than the cereal crops. Cover crops significantly increased AGB and AIPAR in the organic cropping systems but not in CGL. RUE was not significantly affected by the inclusion of cover crops. The use of manure in the organic systems increased AGB, AIPAR and RUE. The results show that AIPAR can be higher in organic cropping systems compared with conventional cropping systems, but this is not translated into a greater yield of cereal crops. There is, therefore, a need for novel approaches to management and the use of biomass in organic cropping systems for increasing yields for feed and food, and which sustains soil fertility.