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The use of copper (Cu) in pig production to stimulate growth and improve feed efficiency is presently being questioned due to the potential environmental hazards associated with the repeated disposal of the resulting Cu rich manure in agricultural land. Results of field experiments conducted on three diverse Virginia soils indicated that the long-term application of Cu as either copper sulfate or Cu rich pig manure, even at high application rates (average application rate for 9 years was 108 metric tons of manure ha⁻¹ year⁻¹ or 32 kg Cu ha⁻¹ year⁻¹), had no adverse effects on corn yields. Copper levels in corn grain and leaf tissue were not increased by the nine annual applications of Cu rich manure or CuSO₄ , except for a slight increase in Cu concentration in corn grain from CuSO₄ application on only one soil. Copper concentrations in all plant tissues were well within normal ranges for all treatments at all sites. Corn grain yields were not decreased by Cu application on any of the three soils. / M.S.

Under the conditions of the Rotation Experiment with Fertilizers, the following results were obtained with corn: The phosphorous plat, complete fertilizer plat and the manure plats produced a much higher yield of corn than the check plat. Also, these plats produced a higher percentage of marketable grain than the other plats. There was not much difference in the shelling percentage from the various plats but it was somewhat lower on the nitrogen and the floats plats. The nitrogen-phosphorous plat produced the greatest number pounds of shelled corn per pound of stover. The complete fertilizer plat also produced a high percentage of grain to stover. The percentage of matured ears was greatly increased on the nitrogen-phosphorous plat and the three manure plats. The corn plants on the manure plat developed sooner than those on the other plats while those of the check plat developed later. Also, the plants were larger in circumference and in height on the manured plat. The means of the corn characters were greater on the fertilized plats than on the check plat, and the means increased as the productivity increased. On the whole, the constants of variation were greater on the fertilized plats than on the check plat. The differences were sufficiently great to indicate that they were significant. On the whole, the coefficients of correlation of the corn characters were greater on the fertilized plats than on the check plat but the odds do not show that they are significant. Opposite results were obtained with wheat which is shown in Table 9. Also, in the case of wheat, the odds on the whole are not significant . In summing up all of the data in this experiment, it may be said that manure and acid phosphate were the chief limiting factors affecting yield. High yield of corn is usually accompanied by a high percentage of marketable grain, high shelling percentage, high ratio of grain to stover, high percentage of matured ears, and early maturity of plants. / Master of Science

Winter-annual cover crops reduce soil erosion by providing ground cover, while producing energy-cheap N for a subsequent crop. Incorporated cover crops or those left as no-till mulch can enhance soil structure and water infiltration. A series of studies was designed to test agronomic advantages of growing mixtures of rye plus hairy vetch and hairy plus bigflower vetches. Plots were arranged in randomized complete blocks and the study conducted for two consecutive cover crop/corn sequences. I measured N yield of cover crops, their ground-covering ability, and their influence on soil structure and a subsequent corn crop. Nitrogen yields ranged from 53 to 187 kg/ha using either pure stands of hairy vetch or mixtures of hairy vetch plus bigflower vetch. Nitrogen yields for rye plus hairy vetch mixtures ranged from 90 to 179 kg/ha. Rye growing in association with vetch had lower C:N ratios (47:1) than pure rye (59:1), apparently deriving additional N from vetch. Vetches were poor at covering the ground in the fall (< 15% cover) as compared to rye (> 41% cover) or mixtures of rye and vetch (25 to 45% cover). When compared to vetch pure stands, corn yields were suppressed 5 to 42% by including rye with vetch due to N immobilization from the rye component and reduced N yield from the vetch component. Corn yields from hairy vetch or hairy: bigflower vetch mixtures were 15.5 Mg/ha and 16.2 Mg/ha respectively and statistically similar to rye + 140 kg N/ha (16.7 Mg/ha). Corn following the two-vetch mixture took up 129 kg N/ha, while corn following hairy vetch took up 114 kg N/ha. Using N fertilizer, corn N uptake was 183 kg N/ha following 140 kg N/ha fertilizer and 213 kg/ha following 210 kg/ha N fertilizer. Increased soil moisture seemed to be related to the presence of a surface mulch. I was unable to detect any changes in water-stable soil aggregates in the upper 15 cm after 2 years of cover cropping. During 1988, water infiltration in no-till plots was lower than in plots that had been disk incorporated, but a tillage effect was not seen in 1989. / Ph. D.

Concerns for environmental quality stimulate the development of various management strategies that mitigate nutrient losses to the environment. / Field experiments were conducted at St. Emmanuel, Quebec, from 1998 to 2000 to investigate the combined effects of water table management and N fertilizer application rates on corn yield, concentrations of NO3- -N in the soil profile and tile subsurface drainage water, denitrification and N2O production rates, and N2O:N2O+N 2 production ratios in the soil profile. There were two water table treatments: free drainage (FD) with open drains at a 1.0 m depth from the soil surface and subirrigation (SI) with a water table depth of 0.6 m below the soil surface, and two N fertilization rates: 120 kg N ha-1 (N120) and 200 kg N ha-1 (N 200) arranged in a split-plot design. Compared to FD, subirrigation reduced NO3--N concentration in the soil by up to 50% and in drainage water by 55 to 73%. Water table had little effect on corn yield during the study period. Greater denitrification rates under SI were not accompanied with greater N2O emissions as ratios of N2O:N2O+N2 were lower under SI than in FD plots. Denitrification rate, N2O emissions, and their ratios were unaffected by N rate. / A second field experiment was initiated from 1999 to 2000 to assess impacts of tillage systems on NO3--N, denitrification, N2O, and ratios of denitrification end-products (N2O:N 2O+N2). The experiment was conducted on long-term momocropped corn experimental plots under conventional tillage (CT), reduced tillage (RT), and no-till (NT), located at the Macdonald Research Farm, McGill University. Soil NO3--N concentrations tended to be lower under RT than under NT or CT. Denitrification and N2O were similar among tillage systems. / Approximately 50% of soil denitrification activity was measured within the 0.15--0.45 m soil layer. Consequently, we propose that sampling the 0--0.15 m soil layer alone, as is usually done, may not give an accurate picture of soil denitrification activity. Dissolved organic carbon concentrations remained high in all soil depths sampled, but was not affected by water table, N rate or tillage system.