Kongoli C E, Bland W L
NOAA/NESDIS/ORA, Atmospheric Research and Applications Division, Camp Springs, MD 20746-4304, USA.
J Environ Qual. 2002 Jul-Aug;31(4):1174-83. doi: 10.2134/jeq2002.1174.
Winter landspreading is an important part of manure management in the U.S. Upper Midwest. Although the practice is thought to lead to excessive P runoff losses, surprisingly little has been learned from field experiments or current water quality models. We captured knowledge gained from winter manure landspreading experiments by modifying a mechanistic snow ablation model to include manure. The physically based, modified model simulated the observed delay in snow cover disappearance and surface energy balance changes caused by application of the manure. Additional model simulations of surface energy balance estimates of radiation and turbulent fluxes showed that during intense melting events the manure on top of snow significantly reduced the energy available for melt of the snow underneath, slowing melt. The effect was most pronounced when snowmelt was driven by both relatively high solar radiation and turbulent heat fluxes. High absorbed shortwave radiation caused significant warming of the manure, which led to substantial losses in turbulent fluxes and longwave radiation. Simulations of snowmelt also showed that manure applications between 45 and 100 Mg ha(-1) significantly reduced peak snowmelt rates, in proportion to the manure applied. Lower snowmelt rates beneath manure may allow more infiltration of meltwater compared with bare snow. This infiltration and attenuated snowmelt runoff may partially mitigate the enhanced likelihood of P runoff from unincorporated winter-spread manure.
冬季田间撒施粪肥是美国中西部上游地区粪肥管理的重要组成部分。尽管人们认为这种做法会导致磷流失过多，但令人惊讶的是，从田间试验或当前水质模型中了解到的情况却很少。我们通过修改一个机理化融雪模型以纳入粪肥，获取了冬季粪肥田间撒施试验所积累的知识。这个基于物理原理的改进模型模拟了因施用粪肥而观察到的积雪消失延迟和地表能量平衡变化。对辐射和湍流通量的地表能量平衡估计进行的额外模型模拟表明，在强烈融化事件期间，积雪上的粪肥显著减少了下层积雪融化所需的能量，减缓了融化速度。当融雪由相对较高的太阳辐射和湍流通量共同驱动时，这种影响最为明显。高吸收短波辐射导致粪肥显著升温，进而导致湍流通量和长波辐射大幅损失。融雪模拟还表明，每公顷施用45至100吨粪肥会显著降低融雪峰值速率，且与粪肥施用量成比例。与裸雪相比，粪肥下方较低的融雪速率可能会使更多融水渗入。这种入渗和减弱的融雪径流可能会部分减轻未混入土壤的冬季撒施粪肥导致磷径流增加的可能性。
