Agronomy and Horticulture Department

 

First Advisor

Cody Creech

Second Advisor

Roger Elmore

Third Advisor

Rodrigo Werle

Date of this Version

Summer 7-31-2020

Comments

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 Cody F. Creech and Roger W. Elmore. Lincoln, Nebraska: July, 2020

Copyright 2020 Alexandre Tonon Rosa

Abstract

With the increased cover crop (CC) popularity, producers of semi-arid regions of western Nebraska are questioning whether they could successfully incorporate CC into their rainfed winter wheat (Triticum aestivum L.)-corn (Zea mays L.)-fallow rotations. The major concern is that CCs may deplete soil water affecting the subsequent crop. Therefore, three studies were established under rainfed conditions of western Nebraska to access the effects of CCs on soil water, soil compaction, nutrient cycling, weed demographics, residue coverage, and subsequent corn yield. The first study evaluated the influence of CC planting and termination times prior to corn establishment. Late termination of CCs in the spring reduced weed density and biomass, but also decreased up to 17% of total nitrogen at 0-10 cm soil depth, and up to 26% of soil nitrate at 10-20 cm soil depth at corn V6 development stage. Cover crops planted early and terminated late had the most detrimental impact on corn grain yield. The second study evaluated the effects of different CC species. Cereal rye increased soil penetration resistance from 20-30 cm depth across site-years. Cover crop growth in the spring suppressed weeds during early corn growing season, especially cereal rye. On the other hand, CCs increased N immobilization (except brassicas) during corn growing season and consequently reduced the corn grain yields compared to fallow (except spring oats). The third study combined CCs and WW stubble height management. In Gothenburg and North Platte sites, the residue coverage biomass was increased by CC mixtures in comparison to fallow. Both CC winter-sensitive and winter-hardy mixtures reduced soil water content during CC growth period, especially from 15-45 cm deep and deeper in the soil profile compared to fallow. Consequently, corn grain yields were reduced in about 17% by CC winter-hardy mixture in all sites, except Gothenburg. The research findings will assist the development of recommendations for CC management in rainfed cropping systems of western Nebraska and Central Great Plains.

Advisors: Cody F. Creech and Roger W. Elmore

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