Enzyme Activity in Response to Fertilizer Application.

Over the past few decades, increases in crop production, especially corn grain yields, have been mainly a result of genetic improvements and plant population. This can easily be observed in yields of control plots from long-term trials where yields have steadily increased over the time even though no fertilizer has been applied to those plots. The advances in technology has allowed the farmer to have a much better view of crop performance throughout a given field by using yield monitor software combined with a GPS system. The use of this technology has shown that even though fertilizer can be applied homogeneously in a field, there will always be areas of high and low yields, this has been termed as field variability. This research was developed to try and understand the nature of this field variability but manipulating C (residue removal or incorporation), N (six rates from 0 to 200 kgNha^-1), P (five rates from 0 to 100 kgP₂O₅ha^-1), and S (four rates from 0 to 20 kgSha^-1) inputs in a continuous corn rotation replicated four times. Soil samples and tissue samples were collected two times during the growing season for nutrient availability and uptake and also for enzyme activity analysis, and grain was harvested at the end of the study for yield and nutrient uptake. The preliminary results showed that C, N and P were the most important factors controlling corn yield and enzyme activities in the soil. Incorporating the residue decreased yield by 19% compared with plots where residue was removed. However, incorporating residue increased enzyme activity, which could have increased microbial uptake of nutrients limiting nutrient availability for the crop.