Graduate Studies

 

First Advisor

Nicolas Cafaro La Menza

Second Advisor

Patricio Grassini

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Agronomy and Horticulture (Crop Physiology and Production)

Date of this Version

12-2024

Document Type

Dissertation

Citation

A dissertation presented to the faculty of the Graduate College at the University of nebraska in partial fulfillment of requirements for the degree of Doctor of Philosophy

Major: Agronomy and Horticulture (Crop Physiology and Production)

Under the supervision of Professors Nicolas Cafaro La Menza and Patricio Grassini

Lincoln, Nebraska, December 2024

Comments

Copyright 2024, Luzviminda Ann Ramos Sazon. Used by permission

Abstract

In high-yield soybean environments, the seed yield is limited by nitrogen (N) supply. However, the response of soybean to N fertilizer application is inconsistent. Understanding the seasonal N uptake dynamics in soybean can provide insights on diagnosing N limitation if soybean. To understand soybean N dynamics, we assessed seasonal trends on dry matter and N accumulation in vegetative organs (leaves, stems, and petioles) from 42 field experiments. Each experiment included a ‘zero-N’ treatment, where crops relied on N supply from soil and biological N fixation (BNF), and a ‘full-N’ that received ample N via N fertilizer addition. Vegetative storage proteins (VSPs) in stems were measured via a detailed proteomic analysis at one site. Similarly, we used a large number of variables from a subset of 35 experiments to identify N-limited fields. We also included had included an 80-N treatment in this subset of experiments to identify fields with a cost-effective yield response to N fertilizer. Seed yield ranged from 4.2 to 7.3 Mg ha-1, with full-N higher by 11% relative to zero-N treatment. The full-N showed increased mobilized N from stems and leaves to seeds due to larger N stored before seed filling. These increases in mobilized N were larger in stems than leaves. Indeed, the VSPs abundance increased by 91% in the full-N relative to the zero-N in the stems. Analysis of yield response to full-N and 80-N indicated that 66% soybean fields were N-limited and amongst these fields, 65% were profitable to 80 kg N ha-1 applied around flowering. Soybean yield response to N fertilizer application can be diagnosed through stem N around flowering. Fields with stem N less than 3 kg N ha-1, between 3-6 kg N ha-1, and higher than 6 kg N ha-1 had 75%, 47%, and near zero chance of profitable yield response to 80-N. Our findings show that stem N plays an important role in meeting seed N demand and can be used to diagnose yield response to N fertilizer in soybean.

Advisors: Nicolas Cafaro La Menza and Patricio Grassini

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