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Impact of manure and compost management on soil organic matter and nitrate dynamics

Amir Sadeghpour1, Sarah Hetrick1, Karl Czymmek1,2, Gregory Godwin1, Quirine Ketterings1
1
Cornell University Nutrient Management Spear Program, 2PRODAIRY

Introduction
When manure is applied in the fall or in spring without incorporation at rates to meet the nitrogen (N) needs of corn, phosphorus (P) often ends up being applied at a rate that exceeds crop removal, leading to an increase in soil test P over time. When soil test P levels are low or medium, this is a desirable way to build P fertility. As soil test P increases, agronomic justification for application is reduced, and the soil may reach a level of P saturation where managing risk of P runoff becomes a priority. It is important for farms that land-apply manure to consider P build up and draw down over time. To reduce the rate of P buildup, manure rates will need to be reduced while meeting N requirements where possible. Immediate incorporation of manure in the spring conserves significant ammonia N and is one way to compensate for lower application of N and also keep P in line. Manure, either in liquid or in more solid form, contains organic material that can contribute to an increase in SOM over time. On the other hand, SOM can be negatively impacted by tillage. Here we show changes in SOM and soil nitrate after surface application of compost and manure at high rates versus lower rate of manure with chisel incorporation in a corn silage system.

Field trial
In 2001, an experiment was initiated in Aurora, NY, on a field that had no prior manure history. The study implemented five replications and six treatments: (1) low rate of composted dairy solids (P-based; 20 tons/acre), (2) high rate of composted dairy solids (N-based; 32 tons/acre), (3) low rate of liquid dairy manure with immediate (within one hour) tillage incorporation (P-based; 7,000 gals/acre), (4) high rate of liquid dairy manure application (N-based; 21,000 gals/acre), (5) zero N control (0 lbs N/acre) and (6) side-dress inorganic N (urea ammonium nitrate) at the recommended rate of 100 lbs N/acre. For field preparation, each plot was chisel-plowed, disked, and rolled using a cultimulcher. The low rate of manure received one extra pass of the chisel-plow (two passes in total) to incorporate the manure directly after application. Corn for silage was planted and harvested from 2001-2006.

What did we find?
Soil Organic Matter:
At the start of the experiment, the SOM was 3.5%. After five years of annual addition of high rates of compost, SOM had increased to 3.9% (Fig. 1). Addition of compost at the low rate did not increase SOM. Applying the high rate of manure did not impact SOM while the tillage-incorporation of the lower manure rate resulted in an 11% decrease in SOM (Fig. 1). The plots that did not receive any manure or compost showed an 18% decrease in SOM compared to the original levels (Fig. 1).

Fig. 1: Soil organic matter. Treatments were HC: high rate of compost; LC: low rate of compost; HM: high rate of manure; LM: low rate of manure; N0: zero N control; and N100: 100 lbs sidedressed N/acre. This figure is comparing soil organic matter in April 2006 with soil organic matter in April 2001 for each fertility treatment.

ig. 1: Soil organic matter. Treatments were HC: high rate of compost; LC: low rate of compost; HM: high rate of manure; LM: low rate of manure; N0: zero N control; and N100: 100 lbs sidedressed N/acre. This figure is comparing soil organic matter in April 2006 with soil organic matter in April 2001 for each fertility treatment.

Soil Nitrate: End-of-season soil nitrate was impacted by fertility management as reflected in the amount of nitrate present in 0-8 inch soil cores collected at three different time periods: immediately after harvest, December before snow, and the following April. We excluded the first two transition years and focused on the last three years of the study (2003-2005). Averaged over growing seasons 4, 5 and 6, once differences were observed, soil nitrate loss in the fall (from September to December) was highest where inorganic N had been used (38% loss). The large decrease in soil nitrate between September and snowfall (December) with inorganic N management of corn reflected N loss through leaching and/or denitrification. In compost amended plots, soil nitrate measured in December was 8% higher than what was measured in September (Fig. 2), suggesting that nitrate mineralization in that time period exceeded nitrate-loss. The same was seen for the plots that had received the lower rate of manure (Fig. 2).

Fig. 2. Soil nitrate (0-8 inches) levels as influenced by fertility treatments from September to April (averaged over 2003-2005). Treatments were HC: high rate of compost; LC: low rate of compost; HM: high rate of manure; LM: low rate of manure; N0: a zero N control; and N100: 100 lbs sidedressed N/acre.

Fig. 2. Soil nitrate (0-8 inches) levels as influenced by fertility treatments from September to April (averaged over 2003-2005). Treatments were HC: high rate of compost; LC: low rate of compost; HM: high rate of manure; LM: low rate of manure; N0: a zero N control; and N100: 100 lbs sidedressed N/acre.

These results suggest that when manure and compost are added, mineralization of organic N into nitrate continues between September and December. The following April, soil nitrate levels were similar among all treatments each year, showing a “reset” of nitrate levels reflecting weather in the fall, winter and spring. The nitrate dynamics for both the inorganic fertilizer plots and the manure and compost plots emphasize the importance of planting cover crop species with the ability to grow rapidly in the fall and to overwinter as some of the N lost between harvest and the planting the next spring could have been captured by winter hardy cover crops.

Conclusions
In this experiment, SOM levels decrease in a tilled corn silage/hay/corn grain rotation, with all but the highest level of carbon addition in the high compost treatments. This suggests that application of manure during the corn years is not enough to improve SOM when regular tillage is also part of the management system. The benefits to increasing SOM are well known. For farms that want to increase SOM, it may be necessary to minimize tillage and include cover crops. A shift from high to low rates of manure and compost decreased end-of-season nitrate in the soil but, when combined with tillage-incorporation of the manure, negatively impacted SOM. Manure injection rather than tillage-based incorporation may counteract the negative impacts of a tillage-based manure incorporation system while conserving N and reducing soil test P buildup over time. Inclusion of overwintering cover crops when manure and compost are applied, will aid in capturing of N mineralized in the fall. This could also help with N supply in the spring as earlier work has shown somewhat suppressed yields with P-based application of manure and compost due to an N limitation.

Relevant References

  • Sadeghpour, A., Q.M. Ketterings, G.S. Godwin, K.J. Czymmek. 2016a. Nitrogen vs. phosphorus-based manure and compost management of corn. Agronomy Journal 108: 185-195.
  • Sadeghpour, A., Q.M. Ketterings, F. Vermeylen, G.S. Godwin, K.J. Czymmek. 2016b. Soil properties under nitrogen- vs phosphorus-based manure and compost management of corn. Soil Science Society of America Journal doi: 10.2136/sssaj2016.03.0086.

Acknowledgments
This material is based upon work that is supported in part by Federal Formula Funds and the National Institute of Food and Agriculture, USDA, under Award no. 2013-68002-20525. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the view of the USDA. We thank Aurora Ridge Dairy Farm for providing the liquid manure. Composted dairy solids were supplied by Willet Dairy (years 1 and 2) and Fessenden Dairy (years 3 through 5). For questions about these results contact Quirine M. Ketterings at 607-255-3061 or qmk2@cornell.edu, and/or visit the Cornell Nutrient Management Spear Program website at: http://nmsp.cals.cornell.edu/.
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