Miscanthus x giganteus yield in a REpeated PLAnting Year (REPLAY) experiment across three sites in Iowa, USA.

Research objectives were to study nitrogen (N) fertilization and age effect on Miscanthus x giganteus (mxg) yield and their interaction. In addition, we studied how establishment conditions affected mxg yield response to N fertilization. This is the first repeated planting year experiment conducted on perennial bioenergy grasses. Data showed that mxg yield response to N fertilization was highly variable. Establishment effects were an important driver of this variability and caused significant changes on the magnitude and direction of one-year-old stands’ response to N fertilization. With repeated planting we compared yield gain from first to second year of growth of different single starts. Yield gain of each single start was different within and between sites. This site-specific response suggests that important biases could be introduced when comparing results across studies if repeated planting is not utilized.

Biomass from mxg plots was sampled annually in winter or early spring after multiple days with freezing temperatures (Table 1). At each harvest, two 1-m2 quadrats per plot were collected by hand at 0.10 m above the soil surface and weighed. In 2016 and 2018, we used a composite subsample to estimate dry matter content. In 2017, the dry weight subsamples were made of 15 randomly collected stems from each plot. Subsamples were weighed in the field and dried to constant mass at 60 °C in a forced air drier. The final mass was recorded and dry matter content was calculated for each plot.

本研究旨在探究氮肥（N）施用及植物年龄对巨型芒（Miscanthus x giganteus，简称mxg）产量及其相互作用的影响。此外，研究还关注了立地条件对mxg产量对氮肥响应的影响。此项研究是首次在多年生生物能源草地上进行的重复种植年实验。数据显示，mxg对氮肥的产量响应具有高度变异性。立地效应是导致这种变异性的重要驱动力，并对一龄植株对氮肥响应的幅度和方向产生了显著改变。在重复种植过程中，我们比较了不同单株在不同年份的产量增益。每个单株的产量增益在同一立地内及不同立地间均存在差异。这种具有立地特异性的响应表明，若未利用重复种植，跨研究比较结果可能会引入重要的偏差。mxg地块的生物质每年在冬季或早春，在经历多次低温冷冻天气后进行采样（见表1）。在每个收获季节，每个地块通过手工收集两个面积为1平方米的样方，并放置于土壤表面0.10米处进行称重。在2016年和2018年，我们使用复合子样来估算干物质含量。2017年，每个地块随机收集了15根茎作为干重子样。子样在田间称重后，在60°C的强制空气干燥器中干燥至恒重，并记录最终质量以计算每个地块的干物质含量。