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Unraveling the interactive controls of tillage, residue, and manure additions on nitrous oxide emissions in grain and silage systems

    Demand for organic food and products is growing and has become one of the fastest growing industries in the United States. Interest is growing to expand the organic acreage to reduce reliance on imported organic grains from overseas of unreliable organic standards. Tillage, cover cropping, and manure addition are the three cornerstones of organic agriculture as well as to a varying degree in conventional systems. These three components can interact in a diverse way to influence soil carbon and nitrogen biogeochemistry to trigger nutrient loss pathways, especially I am looking at greenhouse gas nitrous oxide and methane emissions. In this USDA NIFA (2015-2018) funded project, we are leveraging Penn State Reduced-Tillage Organic Systems Experiment, established in 2011, to achieve our research goals.

Tillage, cover crop, and manure application interact to influence nitrous oxide emissions from organic systems

Aerial image of the Reduced-Tillage Organic Systems Experimental plots

The objectives are:

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1) Quantify nitrous oxide and methane emissions from four three year corn-soybean-winter grain organic rotations varying in tillage, cover crop, and manure management practices. This information would enable calculating the carbon footprint of organic products

 

2) Employ Machine Learning tool Random Forest to predict nitrous oxide emissions by Identifying critical drivers and threshold conditions that trigger emissions

 

3) Identify the microbial source of nitrous oxide emissions by using advanced molecular and isotopomer tools

Random Forest partial dependence plot showing threshold conditions for emissions

Nitrous oxide emissions from a landscape transitioning to the energy crops Miscanthus and switchgrass

    Future liquid fuel demand from renewable sources may, in part, be met by converting the seasonally wet portions of the landscape currently managed for soil and water conservation (CRP, Conservation Reserve Program) to perennial energy crops. However, this shift
may increase nitrous oxide emissions, thus limiting the carbon benefits of energy crops in these landscapes. Particularly high emissions may occur during the transition period when the soil carbon and nitrogen cycling is accelerated due to disturbance, plants are establishing, and
nitrate and water accumulation in converging landscape positions may favor emissions. This project was in collaboration with USDA-ARS and funded by USDOT Sungrant, the USDA AFRI, and the Richard King Mellon FoundationIn (2011-2015). The research questions were:

 

          1) What is the effect of converting CRP lands to switchgrass and            Miscanthus on soil nitrous oxide emissions?


          2) What is the effect of nitrogen fertilization in switchgrass
          on nitrous oxide emissions?

 

          3) How do landscape heterogeneity and land conversion interact            to control nitrous oxide emissions?

 

For more information, please read Saha et al., 2016 & Saha et al., 2018

Simplified hillslope hydrology and nutrient dynamics in a landscape with corn and switchgrass in the upper and lower positions, respectively: implications for nitrous oxide emissions

A novel approach to design temporal nitrous oxide sampling strategy

    The goal was to combine the output of simulation models with
statistical methods to design a robust strategy for nitrous oxide sampling
that is less expensive than a regular fixed interval sampling. The
research questions were:

 

         1) How do different fixed interval sampling frequencies affect the uncertainty in estimating cumulative nitrous              oxide flux?

         

         2) Does the relative error of a given sampling frequency vary across soil, climate, and management scenarios?

 

         3) Is it possible to use simulation models to build decision tree based nitrous oxide sampling strategies that are           cost-effective?

 

    To answer these questions, we simulated and analyzed nitrous oxide emissions in four sites in the United States with diverse soil, climate, management practices, and temporally distinct emission patterns. Classification and Regression Trees (CART, Breiman et al., 1984) and Random Forests (Breiman, 2001; Liaw and Wiener, 2002) analyses were conducted on the daily simulation output to cluster the daily fluxes into groups that can be identified by specific properties (for example, precipitation, evapotranspiration or N fertilization rate in prior days). These properties can become rules for sampling, leading to a decision support tool for field nitrous oxide monitoring.

 

For more information, please read Saha et al., 2017

Soil organic carbon fractions and soil physical health attributes under different land uses in subtropical lower Himalayan ecoregions in the NW India 

    Land use change is very rapid in the lower Himalayan regions in the NW India due to biophysical and socioeconomic reasons. The shift from forest to arable land use has resulted in large-scale depletion of soil organic carbon due to accelerated soil erosion by water. The research objective was to understand the impacts of the forest, grassland, agricultural, and eroded lands on water aggregate stability, carbon storage (particularly in the deeper layers) and SOC fractions in Typic Ustochrepts in lower Himalayas of India.

         

For more information, please read Saha et al., 2011, Saha et al., 2014, & Saha et al., 2015

Soil erosion in northwestern India. 

Photo Credit: Dr. S. S. Kukal

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