Lin Jiajia, Compton Jana E, Leibowitz Scott G, Mueller-Warrant George, Matthews William, Schoenholtz Stephen H, Evans Daniel M, Coulombe Rob A
National Research Council, based at US EPA, Western Ecology Division, 200 SW 35 St., Corvallis OR 97333.
US EPA, Western Ecology Division, 200 SW 35 St., Corvallis OR 97333.
Biogeochemistry. 2018;142:247-264. doi: 10.1007/s10533-018-0532-0.
We constructed a seasonal nitrogen (N) budget for the year 2008 in the Calapooia River Watershed (CRW), an agriculturally dominated tributary of the Willamette River (Oregon, U.S.) under Mediterranean climate. Synthetic fertilizer application to agricultural land (dominated by grass seed crops) was the source of 90% of total N input to the CRW. Over 70% of the stream N export occurred during the wet winter, the primary time of fertilization and precipitation, and the lowest export occurred in the dry summer. Averaging across all 58 tributary subwatersheds, 19% of annual N inputs were exported by streams, and 41% by crop harvest. Regression analysis of seasonal stream export showed that winter fertilization was associated with 60% of the spatial variation in winter stream export, and this fertilizer continued to affect N export in later seasons. Annual N inputs were highly correlated with crop harvest N (r=0.98), however, seasonal dynamics in N inputs and losses produced relatively low overall nutrient use efficiency (41%), suggesting that hydrologic factors may constrain improvements in nutrient management. The peak stream N export during fall and early winter creates challenges to reducing N losses to groundwater and surface waters. Construction of a seasonal N budget illustrated that the period of greatest N loss is disconnected from the period of greatest crop N uptake. Management practices that serve to reduce the N remaining in the system at the end of the growing season and prior to the fall and winter rains should be explored to reduce stream N export.
我们构建了2008年卡拉波亚河流域（CRW）的季节性氮（N）预算，该流域是美国俄勒冈州威拉米特河一条以农业为主的支流，处于地中海气候区。向农田（以草种作物为主）施用合成肥料是CRW总氮输入的90%的来源。超过70%的河流氮输出发生在湿润的冬季，这是施肥和降水的主要时期，而最低输出发生在干燥的夏季。在所有58个支流子流域中平均计算，19%的年度氮输入通过河流输出，41%通过作物收获输出。季节性河流输出的回归分析表明，冬季施肥与冬季河流输出的60%的空间变化相关，并且这种肥料在后期季节继续影响氮输出。年度氮输入与作物收获氮高度相关（r = 0.98），然而，氮输入和损失的季节性动态导致总体养分利用效率相对较低（41%），这表明水文因素可能会限制养分管理的改善。秋季和初冬河流氮输出的峰值给减少氮向地下水和地表水的损失带来了挑战。构建季节性氮预算表明，最大氮损失期与最大作物氮吸收期不相关。应探索有助于在生长季节结束时以及秋季和冬季降雨之前减少系统中剩余氮的管理措施，以减少河流氮输出。
