Biomass productivity and radiation utilisation of innovative cropping systems for biorefinery

Abstract

In order to supply future biorefineries there is a need to sustainably intensify the biomass production on current agricultural land. The aim of this work was to determine biomass yield and associated radiation utilisation for novel perennial grasses and annual crops in rotations optimised for biomass production, and compare their performance with traditional cropping systems commonly used in northern European agriculture. Measurements of biomass yield from 2012 to 2015 at two Danish sites differing in soil type and climatic conditions were conducted in three main cropping systems: i) optimised rotation of annual crops (maize, beet, hemp/oat, triticale, winter rye and winter rapeseed), ii) perennial crops intensively fertilised (festulolium, reed canary, cocksfoot and tall fescue), low-fertilised (miscanthus) or unfertilised (grass-legume mixtures) and iii) traditional systems (continuous monocultures of maize and triticale, and a rotation of spring barley−winter barley−winter rapeseed).The results showed that on sandy loam soil, the highest biomass yield (mean of three years following the establishing year) was achieved by festulolium (20.4Mgha−1), followed by tall fescue (18.5Mgha−1), optimised rotation (16.7Mgha−1), reed canary (15.9Mgha−1) and cocksfoot (15.2Mgha−1). On coarse sandy soil, the highest biomass was achieved by tall fescue (17.7Mgha−1), followed by cocksfoot (15.9Mgha−1), reed canary (14.3Mgha−1) and optimised rotation (13.9Mgha−1). The biomass yield of traditional cropping systems varied between 11 and 18Mgha−1, with continuous maize being the most productive. Although traditional maize produced similar or higher biomass yields than the novel cropping systems, the novel systems are expected to reduce environmental impact and have positive effects on biodiversity.The fraction of intercepted photosynthetically active radiation (fIpar), the accumulated intercepted photosynthetically active radiation (Ipar) and the radiation use efficiency (RUE) were determined from canopy radiations measured biweekly for three years. These results showed a higher annual Ipar (800–1200MJm−2) but lower RUE (1.0–2.0gMJ−1) for the most productive perennial crops than for the most productive annual crops such as maize and beet (Ipar=600–750MJm−2, RUE=2.3–3.0gMJ−1), with variations depending on crop species, management actions and prevailing meteorological conditions. The lower aboveground RUE of perennial crops than of annual crops indicates differences in photosynthesis efficiencies and partitioning of assimilates to non-harvested plant parts and calls for further breeding of the perennial crops to improve their RUE.