green over the winter and resumes growth early in the spring. It adds little organic matter if plowed under in early spring while still small. If allowed to grow until late May, it can reach three to four feet and contribute a fair amount of organic matter. Unless plowed under while quite small, it can be difficult to break up the clumps of winter rye, making it difficult to seed crops.
Some growers prefer oats as a winter cover. Oats should be planted in late summer to make good growth in the fall. Oats winter kill and don't regrow in the spring, making it easy to incorporate them into the soil. If there is time to make good growth in the fall, oats can contribute several tons of organic matter per acre.
Hairy vetch is a legume which some farmers are using as a winter cover. If planted in mid-August and plowed under in spring, it can grow enough to contribute 100 lb or more of nitrogen per acre. Hairy vetch can be planted as late as mid-September, but it won't grow much in the fall, and must be allowed to grow until late May to reach its potential for nitrogen contribution. Most farmers plant vetch in combination with rye or oats.
A number of vegetable growers are growing a summer cover crop to increase SOM. This may involve taking a field out of vegetable production for a season, but an early vegetable crop can be grown and followed by a summer cover crop. A good choice is sorghum-sudangrass. This is a fast-growing plant that looks like skinny corn. It can produce a high amount of organic matter if planted by early July. It grows up to ten or twelve feet high and is difficult to turn under. However, this can be made more manageable by mowing two to three times during the season, whenever it reaches three to four feet.
As we discussed, organic matter is broken down by microbes which use carbon for energy. They also have a high requirement for nitrogen. Microbes have a requirement of about one nitrogen atom for each 25 carbon atoms. This is a carbon-to-nitrogen ratio (C:N) of 25:1 or 25. If the organic matter has a higher C:N, microbes will need more nitrogen than is in the organic matter and will take it from the soil. Microbes are more efficient than crops in obtaining nitrogen from the soil. If there is not enough nitrogen for both the microbes and the crop, the crop will not obtain what it needs. Eventually there will be a net gain in nitrogen, but crops can suffer in the short term. If organic matter with a high C:N is applied to soil shortly before planting a crop, additional nitrogen may be needed to assure that the needs of both the microbe and the crop are met. Organic matter with a C:N of less than 25:1 (25) should not be a problem and in some cases can contribute nitrogen for crop use. Examples of C:N ratios for some sources of organic matter are as follows:
Legume hay 15-19:1
Non-legume hay 24-41:1
Corn stalks 42:1
Oat straw 70:1
Rye straw 82:1
Cow manure 8:1
Finished compost 17-20:1
Agricultural soils 8-14:1
Hardwood sawdust 500:1
We should consider the C:N when incorporating a cover crop into the soil. In recent experiments peppers were planted following: 1) no winter cover crop; 2) winter rye; 3) winter rye plus hairy vetch. The cover crops were plowed down at the end of May. On plots with no nitrogen added, the plants following rye were stunted and yellow compared to those following no cover crop. At the time of incorporation, rye would have had a C:N ratio of well over 25, causing reduced availability of nitrogen to the peppers. The peppers following vetch/rye grew better than either of the other treatments. Apparently, the vetch contained enough nitrogen to supply the needs of both the microbes and peppers.
Crop residues contribute nutrients and organic matter if they are returned to the soil. Residues are usually returned by incorporating them directly into the soil, but on a small scale they can be removed from the field, composted and then returned to the soil. Crops vary considerably in the amount of organic matter and nutrients their residues contribute. An acre of corn stalks can contain several tons of organic matter. About two-thirds of the nutrients taken up by a corn crop go into the stalks and leaves. This is returned to the soil if only the ears are harvested and the stalks are plowed under. Some sweet corn growers sell their corn stalks to dairy farmers who chop them for silage. The going price is about $40 per acre based on the feed value of stalks without ears. This doesn't pay the cost of fertilizer to replace the nutrients lost in the stalks, not to mention the value of the organic matter. The amount of organic matter and nutrients in the unharvested parts of plants varies considerably depending on the crop. For instance, onions or cabbage leave little in the field after harvest. The New England Vegetable Management Guide contains a table and other information regarding nutrient uptake of crops. This information is presented for the part of the crop harvested and the residue left in the field. From this you can estimate the nutrient value in residues of various crops.
Demonstration Vineyard for Seedless
Table Grapes for Cool Climates
Sonia Schloemann, UMass Extension
Reprinted from UMass Berry Notes, Vol. 17, No. 14
This project is designed to evaluate the suitability of seedless table grape varieties for production in a zone 5 climate. This will require multiple years of observation and assessment, particularly with regard to winter hardiness. The project will also seek to develop information for growers on best management practices for successfully growing table grapes in our climate. Once the vines are fully established, demonstration of canopy management, cluster thinning, cane girdling and other treatments can commence. These trials will be guided by work done in other cold climate grape production areas such as Michigan and New York. Significant interest among consumers in seedless table grape consumption, coupled with the availability of many new cultivars with increased winter hardiness, has prompted the need for this type of evaluation. Many tree fruit growers have expressed interest in learning more about viticulture, which makes the inclusion of this project at the UMass Cold Springs Orchard especially appropriate.
(Continued on page 10)