Thesis (Ph. D.)--Michigan State College of Agriculture and Applied Science, 1928. / Includes bibliographical references (p. 28-30).

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Globally, an estimated 25% of the CO2 and 90% of the N2O is believed to come from agroecosystems. The objective of this study was to investigate the dynamics of the below-ground CO 2 and N2O concentrations and efflux in corn and soybean systems. In our field study, changes in the below-ground concentrations of CO 2 and N2O were closely related to seasonal changes in soil moisture, with the first two months of the growing season being particularly critical to the production of these gases. Tillage significantly increased CO2 content in the soil profile, however, this effect was greater in the soybean plots than in the corn plots. In our greenhouse studies, an average of about 79% of the soil respiration in corn came from rhizosphere respiration, compared to an estimated 58% in the case of soybean. Specific rhizosphere respiration was significantly higher in soybean (0.29 mg C g -1 root h-1) than corn (0.09 mg C g-1 root h-1), which supports previous observations made with regards to slower-growing plants (e.g. soybean) having relatively higher root respiration than faster growing plants. We observed a nonsignificant difference between N2O efflux in the soybean-planted soil and unplanted bulk soil, which is in contrast to the perception that legumes could stimulate more N 2O production from the soil by increasing the N pool through N 2 fixation. While corn had the greatest uptake of fertilizer N, N 2O efflux in corn pots was higher (2.84 mug N pot-1 h-1) than the soybean pots (0.06 mug N pot-1 h-1). In the laboratory setting, denitrification in the microaggregates proceeded at about 4.4 to 39.6 times higher rate than in large macroaggregates, small macroaggregates or the bulk soil, and showed the greatest response to high moisture levels (80% WFPS).

Soil phosphate is essential for the development and maturity of crops. Plants absorb phosphate from the soil solution which is continuously replenished by fertilizer application and/or desorption from the soil solid phase. Anion exchange membranes (AEMs), act in a similar way to plant roots, adsorbing P from soil solution. Desorption of available P was studied in 1997 on two Gleysolic soils rich in P, a Ste. Rosalie clay soil and a Duravin sandy loam soil, using fluoride-saturated AEMs let in soil suspension for various contact periods. Determination of available P using these AEMs was compared to P extraction using the Mehlich III extractant for predicting P availability to soybean (Glycine max L.). Desorption from both soils, and subsequent adsorption by AEMs was found to decrease with time. A high P desorption rate was calculated for both soils with the Elovich equation. Different chemical and physical characteristics such as pH, Mehlich III extractable Al, Fe and Ca, sand and clay content were in some cases, positively correlated and in other cases, negatively correlated with various contact periods for both soils. The use of AEMs better predicted P availability than the Mehlich III extractant, although the most important asset of using AEMs is that they showed the desorption effect over time on P availability. It was observed that P remobilization from the vegetative part to the grain was reduced due to the high P concentration in both soils.

Corn (Zea mays L.) production under monoculture and conventional-tillage management may cause soil degradation and nitrate (NO$ sb3 sp-)$ pollution. This study was conducted from 1991 to 1993 to evaluate the impact of conventional-tillage (CT) and no-tillage (NT) practices under corn-soybean (Glycine max L. Merill) rotations (C-S-C and S-C-S), continuous corn (C-C-C) and continuous soybean (S-S-S) systems on optimum N fertilization rates, yield and soil residual N levels. Field experiments were carried out on a Ste. Rosalie clay (Humic Gleysol) and an Ormstown silty clay loam (Humic Gleysol). Overall, tillage had little effect on soil and crop N levels or grain yields. Residual soil NO$ sb3$-N in the fall was related to fertilizer N rates in C-C-C, but not with S-S-S or soybean in rotation. Residual NO$ sb3$-N values after soybean were high and at zero added N were equivalent to 90 kg N with C-C-C. Consequently, soybean contributed the equivalent of 90 kg N ha$ sp{-1}$ to subsequent corn. Corn yields following soybean were higher than following corn, and less fertilizer N was required following soybean than following corn.

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