The effects of maize (Zea mays L.) hybrid and harvest date on above- and belowground biomass dynamics, forage yield and quality - A trade-off for carbon inputs?

There are two major environmental constraints of silage maize (Zea mays L.) production: loss of soil organic carbon (SOC) and nitrogen (N) leaching to groundwater. Winter catch crops (CC) increase carbon inputs and can accumulate residual N, but only if the preceding maize is harvested timely to allow high above- and belowground biomass and N accumulation. To quantify the combined effects of hybrid maize variety and harvest date on forage yield and quality, as well as on root dynamics, root turnover and carbon input, a two-year field experiment (April 2012-October 2013) was conducted in northern Germany. Early maturing Suleyka was harvested at 10 (hd1) and 20 (hd2) September and mid-early Ronaldinio at 30 September (hd3) and 15 October (hd4). Maize hybrids showed no consistent differences of aboveground dry matter (DM) and N accumulation dynamics. Only the very early harvest (hd1) resulted in 11-13% lower DM yields. Sufficiently high DM and starch contents, however, were not achieved at harvest dates prior to hd3 (30 September). Similar to shoot yield, the final accumulated root biomass, carbon (C) and N were not affected by hybrid/harvest date, and on average amounted 2.48 t DM, 1.2 t C and 52.9 kg N ha‐1 in the upper soil depth of 30 cm, which represented between 77 and 75% of the DM, C and N accumulation to 60 cm soil depth. Root turnover during the growing season reached up to 65, 75 and 69% of root DM, N and C. Stubble DM and C left on the field, however, was 31% lower at early harvest (hd1) compared to later harvests, resulting in a trade-off to total C inputs compared to delayed harvest. The quantified C inputs are discussed by two C balance approaches, which indicate that silage maize cultivation is not necessarily associated with SOC degradation, especially if winter catch crops are introduced.