Abstract New Zealand dairy farming systems use considerable maize silage as a supplemental feed, often producing the crop within the farm boundary by cropping a paddock for one or more years then rotating through other areas of the farm. While globally the effects of permanent maize (Zea mays L.) cropping on soil carbon (C) stocks have been studied, little is known about the impact short-duration periodic cropping for maize silage within rotationally grazed pastures has on soil C stocks. In this study, we used the net ecosystem carbon balance (NECB) approach to determine the carbon budget of two maize silage crops in subsequent years and contrasted this with the alternative of grazed pasture on the same farm. Eddy covariance measurements provided CO2 exchange data, which were coupled with measurements or estimates of all other carbon imports and exports of the two systems. We chose to isolate just the period of maize silage production with our measurements extending from the time of herbicide application before planting of the maize crop through to seedling emergence of pasture re-establishment following harvest. The NECB of the maize silage system identified a large loss of C from the ecosystem (–850 g C m−2 and –415 g C m−2 for years 1 and 2 respectively), while the pasture was near neutral in year 1 (11 g C m−2) and a C source in year 2 (–114 g C m−2). Aboveground biomass production from the maize system was three times greater than the pasture system, with >90 % harvested and removed. In contrast, a net of ∼60 % of the aboveground biomass was removed from the pasture system. The large difference in exported biomass, coupled to long establishment periods with no photosynthetic C inputs of the maize were key factors in the much larger C losses from the maize system relative to the pasture.

中文翻译：

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量化永久温带牧场定期玉米青贮作物的碳损失

摘要 新西兰奶牛养殖系统使用大量玉米青贮饲料作为补充饲料，通常在农场边界内生产作物，在围场种植一年或多年，然后轮流穿过农场的其他区域。虽然在全球范围内研究了永久玉米 (Zea mays L.) 种植对土壤碳 (C) 库的影响，但对轮牧牧场内玉米青贮的短期定期种植对土壤碳库的影响知之甚少。在这项研究中，我们使用净生态系统碳平衡 (NECB) 方法来确定随后几年两种玉米青贮作物的碳预算，并将其与同一农场放牧的替代方案进行对比。涡流协方差测量提供了 CO2 交换数据，这与两个系统的所有其他碳进口和出口的测量或估计相结合。我们选择仅隔离玉米青贮生产的时期，我们的测量范围从玉米作物种植前的除草剂施用时间到收获后重新建立牧场的幼苗出现。玉米青贮系统的 NECB 发现生态系统中大量碳流失（第 1 年和第 2 年分别为 –850 g C m-2 和 –415 g C m-2），而牧场在第 1 年接近中性（ 11 g C m-2) 和第 2 年的 C 源（–114 g C m-2）。玉米系统的地上生物量产量是牧场系统的三倍，收获和移除的比例超过 90%。相比之下，从牧场系统中去除了约 60% 的地上生物量。