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Site-specific estimation of corn yield response to nitrogen fertilizer

By Vijaya Joshi, Jeff Coulter
 
Site-specific yield estimation is important for efficient management of agricultural inputs and explaining spatial yield variability. Current approaches for site-specific yield estimation include the use of historical yield maps (Fig. 1), crop simulation modeling, and remote sensing. Several years of historical yield maps provide information on spatial yield variability and help locate higher and lower yield zones in fields. However, the causes of yield variability may differ due to interactions among weather, crop management, and site characteristics such as soil type and topography.
 
 
 
Figure 1. Corn yield map from 2016 (above) and legend (right).
 
Crop models incorporate the effects of cultivar, soil, weather, and agronomic management, and simulate dynamic processes of crop growth, development, and yield. This approach is useful in providing information on yield-limiting factors. However, most crop models assume a uniform unit for application and their point-based simulation restricts their utility at larger spatial scales. At such scales, major limitations arise from the lack of site-specific inputs for model calibration and evaluation. 
 
Remote sensing data from aerial and satellite imagery provide nearly real-time information on crop growth status at larger spatial scales. It has an advantage of rapid, site-specific estimation of crop parameters such as biomass and plant nitrogen (N) content. While the estimated crop parameters can distinguish the spatial yield variability in a field, they have limited application in determining the yield-limiting factors. The use of geospatial data on crop growth parameters from remote sensing with crop models offers an opportunity to improve site-specific estimation of crop yield and determine the most yield-limiting factors.
 
Crop modeling study
 
A study was conducted during 2016 and 2017 at the University of Minnesota Southwest Research and Outreach Center at Lamberton, MN to evaluate a crop modeling approach (CERES-Maize) and an integrated approach of crop modeling with remote sensing (RapidEye satellite imagery) to estimate site-specific corn yield response to fertilizer N. The experiment was carried out across a heterogeneous 17-acre field with and without N fertilizer treatments. The fertilized treatment received sidedress application of urea ammonium nitrate at the six leaf-collar stage (V6) according to university N rate guidelines. Corn biomass at the five (V5) and ten (V10) leaf-collar stages was estimated across the field using regression equations obtained between normalized difference vegetative index (NDVI) and field measured biomass data. The estimated biomass at V5 and V10 stages from satellite imagery were used to spatially optimize the total soil N concentration in the crop model (Fig. 2). 
 
 
Figure 2. Diagram showing the use of remote sensing data with crop modeling for parameter optimization.
 
Results
 
Spatial optimization of total soil N concentration in the crop model improved yield simulations at both the V5 and V10 stages. However, optimization at V10 gave better yield simulations as compared to V5. These findings demonstrate that an integrated approach of crop modeling combined with remote sensing data could provide better simulations of the crop-soil system and improved corn yield estimates as compared to crop modeling alone. This approach could be useful for site-specific estimation of corn yield as well as for the development of spatially variable N fertilizer rate prescriptions.
 

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Moving Ag Research Forward Through Collaboration

Video: Moving Ag Research Forward Through Collaboration



BY: Ashley Robinson

It may seem that public and private researchers have different goals when it comes to agricultural research. However, their different strategies can work in tandem to drive agricultural research forward. Public research may focus more on high-risk and applied research with federal or outside funding, while private sector researchers focus more on research application.

“For me, the sweet spot for public private sector research is when we identify problems and collaborate and can use that diverse perspective to address the different aspects of the challenge. Public sector researchers can work on basic science high risk solutions as tools and technologies are developed. They then can work with their private sector partners who prototype solutions,” Mitch Tuinstra, professor of plant breeding and genetics in Purdue University’s Department of Agronomy, said during the Jan. 10 episode of Seed Speaks.

Public researchers they have the flexibility to be more curiosity driven in their work and do discovery research. This is complimentary to private research, which focuses on delivering a product, explained Jed Christianson, canola product design lead for Bayer CropScience, explained during the episode.

“As a seed developer, we worry about things like new crop diseases emerging. Having strong public sector research where people can look into how a disease lifecycle cycle works, how widespread is it and what damage it causes really helps inform our product development strategies,” he added.

It’s not always easy though to develop these partnerships. For Christianson, it’s simple to call up a colleague at Bayer and start working on a research project. Working with someone outside of his company requires approvals from more people and potential contracts.

“Partnerships take time, and you always need to be careful when you're establishing those contracts. For discoveries made within the agreement, there need to be clear mechanisms for sharing credits and guidelines for anything brought into the research to be used in ways that both parties are comfortable with,” Christianson said.

Kamil Witek, group leader of 2Blades, a non-profit that works with public and private ag researchers, pointed out there can be limitations and challenges to these partnerships. While private researchers are driven by being able to make profits and stay ahead of competitors, public researchers may be focused on information sharing and making it accessible to all.

“The way we deal with this, we work in this unique dual market model. Where on one hand we work with business collaborators, with companies to deliver value to perform projects for them. And at the same time, we return the rights to our discoveries to the IP to use for the public good in developing countries,” Witek said during the episode.

At the end of the day, the focus for all researchers is to drive agricultural research forward through combining the knowledge, skills and specializations of the whole innovation chain, Witek added.

“If there's a win in it for me, and there's a win in it for my private sector colleagues in my case, because I'm on the public side, it’s very likely to succeed, because there's something in it for all of us and everyone's motivated to move forward,” Tuinstra said.