Planting cover crops after corn-silage harvest could have a critical role in the recovery of residual N and N from fall-applied manure, which would otherwise be lost to the environment. Experiments were conducted at the University of Massachusetts Research Farm during the 2004-2006 growing seasons. Treatments consisted of oat and winter rye cover crops, and no cover crop, and four cover-crop dates of planting. The earliest planting dates of oat and winter rye produced the maximum biomass yield and resulted in the highest nitrate accumulation in both cover-crop species. The average nitrate accumulation for the 3 years in winter rye and oat at the earliest time of planting was 60 and 48 kg ha -1 , respectively. In 2004 where the residual N level was high, winter rye accumulated 119 kg nitrate ha -1 . While initially soil N levels were relatively high in early September they were almost zero at all sampling depths in all plots with and without cover crops later in the fall before the ground was frozen. However, in plots with cover crops, nitrate was accumulated in the cover-crop tissue, whereas in plots with no cover crop the nitrate was lost to the environment mainly through leaching. The seeding date of cover crops influenced the contribution of N available to the subsequent crop. Corn plants with no added fertilizer, yielded 41% and 34% more silage when planted after oat and rye, respectively, compared with the no-cover crop treatment. Corn-silage yield decreased linearly when planting of cover crops was delayed from early September to early or mid-October. Corn-ear yield was influenced more than silage by the species of cover crop and planting date. Similar to corn silage, ear yield was higher when corn was planted after oat. This could be attributed in part to the winter-kill of oat, giving it more time to decompose in the soil and subsequent greater release of N, while the rapidly increasing C : N ratio of rye can lessen availability to corn plants. Early plantings of cover crops increased corn-ear yield up to 59% compared with corn-ear yield planted after no cover crop.

Time of planting plays a critical role in nutrient recovery from soils by a winter rye (Secale cereale L.) cover crop. A delay in planting can signifi cantly decrease cover crop performance. Th is study evaluated cover crop planting dates for diff erent areas of Massachusetts using a spatial model based on growing degree days. Field studies were conducted during 2004 through 2009 to estimate biomass production and nutrient recovery of rye under various planting dates from mid-August to early October. A spatial model identifi ed the critical planting date (CPD) for all locations in Massachusetts based on fi eld studies combined with long-term weather data collected from 14 weather stations. In eastern areas of Massachusetts (Zone 5), CPD is the third week of September. In this region, there is adequate time for planting winter rye aft er corn (Zea mays L.) is harvested. Critical planting dates for central parts of the state ( Zones 3 and 4) are from the fi rst to second weeks of September. Growers in these regions should consider alternative management strategies including selection of shorter season corn hybrids to meet the suggested cover crop planting dates. Th e suggested critical planting dates (third-fourth week of August) for northwest regions of Massachusetts (Zones 1 and 2) may not be practical because corn silage is usually not ready for harvest until mid-September. Th e model can be a powerful decision-making tool for researchers and farmers, not only for winter rye in Massachusetts, but it also can be adapted for use with other cover crop species and for use in other regions where cover crops are grown. A. Farsad,

Leaching of chemicals (e.g., fertilizers, manure, pesticides, and petroleum products) from urban regions and areas impacted by human development is one of the main sources of underground nonpoint‐source pollution. Most methods of soil water sampling are not capable of extracting representative soil water samples to determine leaching volume and solute concentrations since they fail to create normal leaching conditions in the soil. Thus the volume of soil‐water collected, as well as its solute concentration, may not be accurately estimated. Sixteen units of cost effective and accurate automated lysimeters were designed and installed to measure post‐harvest nitrate leaching from a rye (Secale cereale L.) cover crop field during the falls and winters of 2007 to 2009. Major parts of the electronic system were electronic controller, data logger memory, digital clock and its battery backup circuit, relays, LCD display and electronic signal conditioning interfaces for amplifying, off‐setting, and digitizing the signals from vacuum sensors. The electronic system was designed to monitor soil tension every second with accuracy of 1 cm and apply the proper amount of suction to the sampling media (ceramic plate). Hourly data from soil tension and vacuum applied to the system were collected and stored by each unit. A safety system was designed for protecting the vacuum pump against unexpected major vacuum leakage events. The controller can be easily reprogrammed for different performance strategies. The automated lysimeter showed an accurate and reliable performance in both lab and field conditions. Ambient soil matric pressure and matric pressure above the samplers indicated a strong linear correlation which confirms that the lysimeter was successful in maintaining the sampler vacuum in equilibrium with soil.

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