Graduate Thesis Or Dissertation
 

The effect of soil acidity and lime placement on root growth and yield of winter wheat and alfalfa

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  • The application of lime to an acid Nekia soil significantly increased the yield of winter wheat and alfalfa in a field experiment. Crop yields maximized when the lime was partially mixed into the surface four inches of the soil. Thorough mixing of the lime into the surface six inches of soil did not increase crop yields over partial mixing of lime, and on some plots the yields were reduced by the more thorough mixing treatment. The reduction in yield on the thoroughly mixed plots occurred with the lower rates of lime application. Deterioration of soil structure due to rototilling was also a factor in the reduction of yield in the plots where the lime was thoroughly mixed. The yields of wheat decreased over a three-year period following the application of one ton of lime per acre. It was felt that part of this decrease in yield was caused by a more thorough mixing of the lime into the soil with annual seedbed preparation on the partially mixed plots, and by a decrease of Ca and increase of Al in the soil solution as the quantity of free lime in the soil decreased. The importance of the soil solution pH and Al and Ca concentrations in the soil solution is also demonstrated by the fact that the R 2 values for the relationship between the soil test pH and wheat yields, were highest for the 1 N KC1 pH values the first two years, and highest for the water pH value the third year. Third-year wheat yields were also decreased by an infestation of the root fungus, Ophiobolus Graninus, with the adverse effect on the yield decreasing as the lime rates increased. High levels of soil acidity adversely affected the survival of the alfalfa seedlings and the rhizobia which inoculate the alfalfa. The concentration of nitrogen in the plants and the quantity of nitrogen harvested in the plants, increased as the rate of lime applied increased. The wheat and alfalfa roots which grew in the unlimed soil exhibited Al-toxicity symptoms. The Al-toxic roots were thicker than the healthy roots, and there was very little lateral root development on the Al-affected roots. The application of the intermediate and high rates of lime to the acid Nekia soil eliminated the Al-toxicity symptoms and promoted the growth of fine fibrous root systems. The distribution of the alfalfa roots in the samples taken from the field experiment, corresponded with the distribution of the lime in the soil. The field experimental data showed that the yields of wheat and alfalfa were closely correlated to the weight of the root samples. Growth chamber experiments using winter wheat as an indicator crop and acid Nekia and Dayton soils were also conducted. Maximum yields of dry matter were harvested when 30 per cent of the total soil volume was limed, and the dry matter yield decreased as the low rate of lime was mixed into larger volumes of soil. The wheat roots grew in the limed portion of soil, whereas root growth was restricted in the unlimed soil. Plant analysis data showed that the concentrations of plant nutrients were similar for all lime treatments. Plant water potential data indicated that water stress induced by Al-toxicity of wheat roots contributed to the lower yields of wheat grown in soil receiving zero and one ton of lime per acre.
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