Date of Award
Doctor of Philosophy
T. C. Kaspar
Field, growth-chamber, and constant-temperature room experiments were conducted over three years to determine if corn residue exerts toxic effects on corn growth and yield. All three experiments showed that corn residues are toxic, and that this toxicity varies depending on the residue type and the corn genotype grown. Each experiment tested eight genotypes for residue tolerance. In the field studies, some genotypes, such as B73 and A632 x H99, had reduced yields when grown in no-till fields that retained residue. These yield reductions, however, were quite variable depending not only on the residue in the fields, but on all the other environmental conditions influencing crop growth. More detrimental than no-tillage was the effect of corn residue in a continuous-cropping system. When corn was grown every year in a field, drastic yield reductions occurred. Fields cropped to B73 x LH38 showed yield decreases when B73 x LH38, B73, or LH38 were grown the next year. Corn grown in plots that were continuously cropped and no-tilled had shorter plant heights, fewer leaves, less leaf area, higher field moistures, less dry matter accumulation, slower silking and tasseling, lower plant populations, fewer ears, and less yield than plots that were fall plowed and previously fallowed. In the growth-chamber experiments, residues incorporated in the potting soil reduced plant heights, leaf numbers, and harvest dry weights. Generally, the hybrid residues used were more toxic than the inbred residues. The genotypes grown, however, did not differ in their tolerance to individual residues. In the constant-temperature room experiment, the two residue extracts tested also showed different toxicity levels. These extracts effected seedling shoot length, root length, and dry weight. The extracts did have varying inhibitory effects on the genotypes grown. By sequentially eliminating environmental factors that could cause reduced crop growth, these three experiments indicate that residue can be toxic to subsequent crop growth and yield.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Denise Ann McWilliams
McWilliams, Denise Ann, "Tillage and continuous cropping influence on corn genotypes " (1988). Retrospective Theses and Dissertations. 9699.