Fortuna, A. M. 2001. Management of cropping system and compost additions for enhanced nitrogen availability and carbon sequestration. Ph.D. Dissertation, Michigan State University, East Lansing, Michigan, USA.

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The uniformity, low cost and ease of application associated with inorganic fertilizers have diminished the use of organic nutrient sources. Concern for food safety, the environment and the need to dispose of animal and municipal wastes have focused attention on organic sources of N such as animal derived amendments, green manures, and crop rotations. Providing nutrients to row crops from organic sources demands intensive management of the N and C cycles. Managing organic N sources to provide sufficient N at the grand phase of crop growth requires knowledge of C and N decomposition over several years particularly where manure and compost is applied. Management practices of this trial included: a comparison of compost and chemical fertilizer, use of a corn-corn-soybean-wheat rotation compared to continuous corn and the addition of a cover crop within each cropping system. Management strategies that reduced potential nitrification rates without limiting plant available N tended to increase plant biomass to N content (PNC), the above ground net primary productivity (ANPP) per unit of N in ANPP, and decrease the amount of NO 3 – available for leaching, and/or conversion to N 2 O. Nitrification potentials of integrated-compost treatments were 25% lower than integrated-fertilizer treatments during 1998 and 1999. Integrated-compost increased plant PNC (104-137 g g -1 N) above that of integrated-fertilizer (88 g g -1 N). Lowered soil N levels in compost managements decreased nitrification potential and the potential for NO 3 – leaching but diminished corn yield in some treatments and may have reduced grain quality.

Soil samples were taken in April prior to tillage from a 0-25 cm depth in the 2 nd (1994) and 6 th year (1998) of the experiment. These soils were used to conduct N (150 d) and C incubations (320 d) to determine the effect of cropping system and nutrient management on: N mineralization potential (NMP), the mineralizable organic N pool (No), the mean residence time (MRT) of No, C mineralization (C min ), and soil organic carbon (SOC) pool sizes and fluxes. Compost applications increased the resistant pool of C by 30% and the slow pool of C by 10%. The compost treatment contained 10% greater soil organic C than the fertilizer management. Nitrogen was limiting on all compost treatments with the exception of 1 st y corn following wheat fallow and clover cover crop. The added diversity of the clover cover crop and wheat-fallow increased inorganic N in both nutrient managements. We recommend that growers adjust their N fertilizer recommendation to reflect the quantity and timing of N mineralized from organic N sources. Proper management of nutrients from compost, cover crops and rotations can maintain soil fertility, improve soil quality, and increase sequestration.

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