Comparative Effects of Nitrogen and Sulfur Fertilization and Liming on Three Crops Grown on Four Soils

Two consecutive crops of corn (Zea mays L.), soybeans (Glycine max (L.) Merrill), and bromegrass (Bromus inermis) were grown in the greenhouse on four soils to 1) compare degree of response of these three crops to nitrogen and sulfur fertilizations as affected by overall soil characteristics; 2) evaluate the effect of soil characteristics on the relationship of dry matter production and plant N content; and 3) evaluate the N/S ratio and plant N content as indicators of adequacy of N for maximum dry matter production of these crops. The crops and soils were selected to give a wide range in crop and soil characteristics which would serve as a basis for concurrent comparisons. Dry matter production and plant N and S contents were determined. Regression procedures were used to develop response surfaces for the effect of N and S applications on these measured variables. Curves relating dry matter production with plant N content were examined for relationships among soils. Correlation was used to compare plant N content and N/S ratio as indicators of N supply for the plants. Response to nitrogen was common for corn and brornegrass but occurred to a smaller extent for soybeans. Although the magnitudes of N responses varied with the soil type, they were not closely related to soil organic matter or nitrate levels. Response to S was more evident during the second growing period than during the fist period. Soybeans responded to S application only on the sandy Thurman soil. Interactions of N and S applications were observed primarily where large main effects of each of the fertilizers were observed. The CaCO, had little effect on crop growth. The curves relating dry matter production to N content of the corn plants were essentially the same for all but one soil, whereas those for bromegrass were less similar. For soybeans, these two quantities were negatively related in several cases, indicating increasing plant growth with decreasing N content in the plant. The N content of the plant was more closely related to dry matter production than was the N/S ratio.