ALTERING SOIL CARBON AND NITROGEN STOCKS IN INTENSIVELY TILLED TWO-YEAR ROTATIONS

Authors: Griffin, Timothy; PORTER, G - UNIVERSITY OF MAINE

Submitted to: Biology and Fertility of Soils
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/20/2003
Publication Date: 2/20/2004
Citation: Griffin, T.S., Porter, G.A. 2004. Altering soil carbon and nitrogen stocks in intensively tilled two-year rotations. Biology and Fertility of Soils. 39: 366-374

Interpretive Summary: Declining soil organic matter is a serious problem in long-term potato production systems. Potato production includes several tillage operations and relatively small amounts of residue are returned to the soil. Several management options might help either maintain or improve the organic carbon and nitrogen pools in soil, ranging from the addition of cover crops or green manure crops to the application of compost, manure, or other amendments. We used soil samples from six field experiments in Maine that lasted from 6 to 13 years, to examine the effect of these management options on carbon and nitrogen pools in the soil. We determined that amendments were required to increase total carbon or nitrogen levels in the soil, applied occasionally or every year. The amount of carbon and nitrogen in clover cover crops or green manure crops was small compared to the total amount already in the soil. Cover crops and green manure did increase the amount of nitrogen found in organic matter around sand particles, called particulate organic matter. This organic matter pool is directly involved in nutrient cycling and in holding soil particles together. The application of any amendments could, in some cases, double the amount of carbon and nitrogen in this pool. The differences in the amount of carbon present in different forms, including carbon in the soil microbes, was a result of differences in the amount of carbon returned to the soil. This research shows that application of amendments is generally needed to change carbon and nitrogen levels in 2-yr potato rotations.

Technical Abstract: Declining soil organic matter is a serious problem in long-term potato production systems. Several management options might help either maintain or improve the organic carbon(C) and nitrogen(N) pools in soil, ranging from the addition of cover crops or green manure crops to the application of compost, manure, or other amendments. Archived soil samples from field experiments in Maine were used to assess the effect of cover crop, green manure crop, and intermittent or annual amendment on soil (C) and (N) pools. These field experiments, of 6-13 yr duration, were all characterized by 2-yr rotation with either sweet corn (Zea mays L.) or potato (Solanum tuberosum L.), and primary tillage each year. Total, particulate organic matter (POM), and microbial biomass (SMB) C and N pools were assessed for each experiment. Total C and N stocks were not affected by red clover (Trifolium pratense L.) crop or legume green manure, but were increased by 25-53% via single or annual amendment. Likewise, soil microbial biomass C and N were minimally affected by changes in cropping sequence, but were quite sensitive to amendments, even those that were primarily C. Particulate organic matter (POM) C and N, associated with the coarse mineral fraction (53-2000 microns) were more responsive to management factors, and these fractions exhibited proportionally greater increases than total C and N. The change in soil C fractions was a linear function of increasing C supply, across all experiments and treatments. Within these intensively-tilled production systems, substantial C and N inputs from amendments are needed to significantly alter soil C and N pools, although cropping sequence changes can influence more labile pools responsible for nutrient cycling.