Abstract

<p>The incorporation of a comprehensive crop module in land surface models offers the possibility to study the effect of agricultural land use and land management changes on the terrestrial water, energy and biogeochemical cycles. It may help to improve the simulation of biogeophysical and biogeochemical processes on regional and global scales in the framework of climate and land use change. In this study, the performance of the crop module of the Community Land Model version 5 (CLM5) was evaluated at point scale with site specific field data focussing on the simulation of seasonal and inter-annual variations in crop growth, planting and harvesting cycles, and crop yields as well as water, energy and carbon fluxes. In order to better represent agricultural sites, the model was modified by (1) implementing the winter wheat subroutines after Lu et al. (2017) in CLM5; (2) implementing plant specific parameters for sugar beet, potatoes and winter wheat, thereby adding the two crop functional types (CFT) for sugar beet and potatoes to the list of actively managed crops in CLM5; (3) introducing a cover cropping subroutine that allows multiple crop types on the same column within one year. The latter modification allows the simulation of cropping during winter months before usual cash crop planting begins in spring, which is an agricultural management technique with a long history that is regaining popularity to reduce erosion and improve soil health and carbon storage and is commonly used in the regions evaluated in this study. We compared simulation results with field data and found that both the new crop specific parameterization, as well as the winter wheat subroutines, led to a significant simulation improvement in terms of energy fluxes (RMSE reduction for latent and sensible heat by up to 57 % and 59 %, respectively), leaf area index (LAI), net ecosystem exchange and crop yield (up to 87 % improvement in winter wheat yield prediction) compared with default model results. The cover cropping subroutine yielded a substantial improvement in representation of field conditions after harvest of the main cash crop (winter season) in terms of LAI magnitudes and seasonal cycle of LAI, and latent heat flux (reduction of winter time RMSE for latent heat flux by 42 %). Our modifications significantly improved model simulations and should therefore be applied in future studies with CLM5 to improve regional yield predictions and to better understand large-scale impacts of agricultural management on carbon, water and energy fluxes.</p>

Highlights

  • 35 Crop yield is highly influenced by environmental conditions – weather, nutrient availability, atmospheric CO2 – and agricultural practices such as irrigation and fertilizer application

  • The improvement in simulated energy fluxes is in accordance with the results presented in the previous chapters (4.1 and 4.2) where 580 results are analysed for each crop functional types (CFT) respectively

  • The default Community Land Model version 5 (CLM5) was extended by adopting the winter wheat representation of Lu et al (2017), by including crop specific parameterization for winter wheat, sugar beet and potatoes and by the addition of a cover cropping subroutine that allows several growth cycles within one year

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Summary

Introduction

35 Crop yield is highly influenced by environmental conditions – weather, nutrient availability, atmospheric CO2 – and agricultural practices such as irrigation and fertilizer application. Global climate change is widely believed to have an important impact on future agriculture and food security under changing climate is an important research topic (Lobell et al, 2011; Aaheim et al, 2012; Ma et al, 2012; Gosling, 2013; Rosenzweig et al, 2014). 40 increasing irrigation requirements (Urban et al, 2012; Challinor et al, 2014; Deryng et al, 2014; Rosenzweig et al, 2014; Tai et al, 2014; Levis et al, 2018). General agricultural practices have adapted to changes in climate and inter-annual climate variability by adjusting irrigation amounts and fertilizer application as well as cultivating more resistant varieties of certain crops (Kucharik et al, 2006; Kucharik, 2008). The biogeochemical effects and benefits of cover crops as well as their potential to mitigate climate change are the focus of many studies

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