Degree Type

Dissertation

Date of Award

1981

Degree Name

Doctor of Philosophy

Department

Agronomy

Abstract

Critical nutrient percentage is defined as the nutrient concentration associated with maximum yield with respect to the nutrient. Objectives of this research were: (1) to compare three methods for calculating maximum yields and associated critical % N and to determine effects of time of leaf sampling at or near silking on critical % N; (2) to determine effects of P fertilizer rates on critical % N and of N rates on critical % P; and (3) to determine effects of crop sequence, plant density, and moisture stress on critical % N and % P in both grain and leaf. Data were from 39 fertilizer experiments at 4 outlying research centers in Iowa;The direct regression method (yield on % N in the plant part) was generally poorer for estimating critical % N in the grain and leaf than the two-step method (yield and % N on N rates) or graphical method (highest yield based on significance and associated % N). The latter two were similar. Time of leaf sampling and weather factors prior to and during silking affected % N of treatments and critical % N;The P rates increased critical % N in grain as much as 0.12% and that in the leaf as much as 0.16%. As N rates increased, critical % P decreased as much as 0.028% in the grain and increased as much as 0.058% in the leaf. The critical % N and % P in the grain or leaf can evaluate N and P fertility status of corn better if levels of both are considered;The critical % N and % P in both grain and leaf were slightly less in C2 than in C1 in a C1-C2-soybean rotation. Increased stand level decreased critical % N slightly;Moderate-severe moisture stress increased critical % N 0.13% in the grain and decreased it 0.20% in the leaf in an N rate experiment (7 years). In an NP experiment (5 years), similar stress increased grain critical % N 0.14 to 0.23%, decreased leaf critical % N 0.07 to 0.17%, decreased grain critical % P as much as 0.017% and decreased leaf critical % P by 0.019%;In regressions of critical % N from 26 site-years, moisture stress prior to silking increased critical % N in the grain as much as 0.34%. In regressions from 21 site-years, stress after silking decreased leaf critical % N as much as 0.43%. In summary, several factors significantly affected critical N and P percentages in corn grain and leaf.

DOI

https://doi.org/10.31274/rtd-180813-11450

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Luiz Eugenio Coelho de Miranda

Language

en

Proquest ID

AAI8128841

File Format

application/pdf

File Size

328 pages

Share

COinS