Conserving end-of-season N with effective seeding dates for cover crops based on fall growing degree days

Conserving end-of-season N with effective seeding dates for cover crops based on fall growing degree days

Summary

Our hypotheses are i. that fall-winter losses of N leaching in corn fields are avoidable, and can be reduced or prevented if cover crops are used, and are planted early enough to be effective, and ii. that use of cover crops and nutrient management has economic benefit to the farmer, can be integrated into the cropping system through outreach and education, and is transferable to other regions. However, farmers are often impacted by adverse weather conditions and they have difficulty in meeting the planting dates for optimum end-of-season N accumulation. Use of early planting of early maturing corn hybrids can be helpful. On-farm and research trials have shown early hybrids on average have similar yield and improved quality compared to late season hybrids.

Objectives/Performance Targets

Our objectives are i. to determine critical seeding dates and a growing degree day (GDD) model for rye cover crops. ii. To evaluate methodologies for early establishment of cover crops, and iii. to demonstrate the economic benefit of adopting “effective” cover crops.

Of 20 dairy/livestock farmers who participate in on-farm studies and farm based outreach, 15 will use the developed assessment methods for cover crop effectiveness in recovering end-of-season nutrients, and 10 will make management decisions (changes) to ensure cover crops are effective for N uptake.

Accomplishments/Milestones

1. In the 2007-2008 two cover crop farm demonstrations with different cover crop planting dates were established. These were monitored after winter for crop survival and N contribution in spring of 2008. One of these studies was evaluated for growth of corn following the incorporation of the rye cover crops, and several additional farm demonstrations were established as described below.

2. Because inter-seeded cover crops into corn proved less than successful at the 8 farm locations in 2006 (and confirmed by others when presented at the 2008 New England CCA meeting) the alternative 2007 strategy was followed again in 2008. Cover crops in corn silage production were viewed as part of a total production system. The limitation to planting cover crops early for fall N accumulation is in part because the harvest date of corn is often too late for effective establishment of the cover crops. Therefore, our approach in 2008 followed that of the previous year where we involve farmers in an evaluation of yield potential of early hybrids comparing them to the later maturing hybrids they usually plant, and in time of planting studies since early planting helps ensure higher yield and an earlier corn harvest. We have started to expand this data base on yield potential of early season corn hybrids through similar evaluations in Maine and Vermont.

3. Again, in 2008 visits were made to farms involved in cover crop planting, early hybrid evaluations and time of planting trials. The on-going evaluations of cover crop seeding dates, early vs. late hybrid for yield and maturity date, and time of planting hybrids of different maturities were continued at the UMass Crops Research and Education Center.

4. Data from evaluations in 2007 were summarized and discussed at a three farmer research group meetings (two in March, one in July, 2008) with other farmers also involved. Similar meetings will be held in early spring 2009. More than 20 farmers were present at each of the spring meetings and 35 at the summer meeting. Two field days were held at the UMass Crops Research and Education Center and one at a participating farm where cover crops, corn hybrid yield and maturity evaluations and nitrogen conservation were discussed.

5. Results were again presented at the New England Certified Crop Advisors meeting in January 2008.

6. Work on growing degree model continues and graphs were shown in education programs in 2008. This work is being refined after compiling more growth and temperature data in this third year and GIS maps for seeding dates and fall GDDs are being developed.

7. Because of farmer interest and difficulty in achieving early planting of cover crops in a wet year as occurred in 2008 when corn maturity was delayed, we examined a further strategy to conserve N from fall applied manure. When manure is applied to the soil surface ammonia N can be lost to the atmosphere. Such losses can represent 50% of the manure N if all the ammonia N is lost. Our approach has been to examine the effect of temperature on ammonia volatilize from surface applied manure. Preliminary data indicates less ammonia is volatilized with cooler temperatures in late October or early November. We are hopeful if farmers can plant a cover crop by second or third week of September and then later apply the manure in October or November before soils freeze, that more N will be accumulated or held in the soil by the cover crop. This time of cover crop planting in mid September is the normal time for erosion control but two weeks too late for optimum N accumulation by a cover crop when planted following the application and incorporation of manure in the early fall after corn harvest.

Impacts and Contributions/Outcomes

1. Early establishment of cover crops was confirmed in three years of field studies for effectiveness in end-of-season N uptake. On-farm studies early seeded cover crops accumulated 100 lb N/ac from the fall applied manure and carryover N from the previous corn crop when seeded in the first week of September in Massachusetts. On incorporation the following corn crops had PSNT levels exceeding 25 ppm in June. Cover crops seeded on or after September 15 had PSNT levels below this threshold.

2. Growing degree day (GDD) analysis has shown that GIS maps relating GDDs to farm locations can be used as a decision aid for farmers wishing to seed effective cover crops.

3. Results of the early hybrid evaluation has shown planting early with early season corn hybrids can enable farmers to achieve high yields equivalent to late season hybrids and gain the added benefit of end-of-season N accumulation with effective cover crops.

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