As you lucky ones get to work in your patches (I still have have a 4 foot snowdrift over mine) remember to keep the Carbon/Nitrogen ratio in mind when tilling in organic matter. If you have a high C:N ratio (greater than 30:1) this could tie up your N for this year as the organic matter decomposes. A low C:N ratio (less than 28:1) will release N as the organic matter decomposes.
Some C:N ratio for common things are: hay 12:1, rotted manure 15:1, grass clippings 19:1, fruit wastes 35:1, leaves 60:1, corn stalks 60:1, straw 80:1, sawdust 500:1, wood 700:1.
You will not lose the N it will only be released at a much later date depending on what the ratio is and length of decomposition. You can also mix organic material to lower the C:N ratio (ie three parts grassclippings and one part straw will give about a 34:1 ratio; (19+19+19+80)/4=34.25).