Christof Kluß

Effects of catch crops on silage maize (Zea mays L.): yield, nitrogen uptake efficiency and losses

Under the climatic conditions of north-western Europe, silage maize (Zea mays L.) production optimized with respect to nitrogen (N) fertilization and crop rotation is required to reduce N losses. Whether winter catch crops (CC) can serve as a beneficial biological tool in terms of N-loss abatement as well as maize yield also under optimized N management, is unclear. Therefore, a 2-year field experiment was conducted to study the short-term effects of a continuous maize-catch cropping system on maize yield performance, N2O emission and N leaching, as affected by maize harvest/CC sowing date (10, 20, 30 September and 15 October, respectively, hd1–hd4) and CC species (rye, Secale cereale L. and Italian ryegrass, Lolium multiflorum Lam.). Treatments without CC served as control and N fertilization was applied as synthetic N to better adjust to maize N demand. The CC treatment (with or without) had no effect on maize dry matter and N yields, but the N uptake efficiency of maize responded significantly to the N accumulation (Ntot) of CC. Nitrate leaching mostly stayed below the critical load value for EU drinking water and rye significantly reduced nitrate leaching, given that environmental conditions allowed sufficiently high CC biomass accumulation. Annual nitrous oxide emission was unaffected by CC treatment. Restricted N fertilization of maize following CC led to N deficiency, since CC decomposition obviously was not synchronized with maize N demand. Under the given environmental conditions, rye may serve as beneficial CC in continuous maize cropping even in already optimized N management.

Can arable forage production be intensified sustainably? A case study from northern Germany

Abstract. Greenhouse gas emissions (GHG) resulting from forage production contribute a major share to ‘livestock’s long shadow’. A 2-year field experiment was conducted at two sites in northern Germany to quantify and evaluate the carbon footprint of arable forage cropping systems (continuous silage maize, maize–wheat–grass rotation, perennial ryegrass ley) as affected by N-fertiliser type and N amount. Total GHG emissions showed a linear increase with N application, with mineral-N supply resulting in a steeper slope. Product carbon footprint (PCF) ranged between –66 and 119 kg CO2eq/(GJ net energy lactation) and revealed a quadratic or linear response to fertiliser N input, depending on the cropping system and site. Thus, exploitation of yield potential while mitigating PCF was not feasible for all tested cropping systems. When taking credits or debts for carbon sequestration into account, perennial ryegrass was characterised by a lower PCF than continuous maize or the maize-based rotation, at the N input required for achieving maximum energy yield, whereas similar or higher PCF was found when grassland was assumed to have achieved soil carbon equilibrium. The data indicate potential for sustainable intensification when cropping systems and crop management are adapted to increase resource-use efficiency.