Residual impact of raw and composted poultry litter on soil carbon pools

Authors: Cavigelli, Michel; Dao, Thanh

Submitted to: Electronic Journal of Integrative Biosciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/13/2008
Publication Date: 12/29/2008
Citation: Cavigelli, M.A., Dao, T.H. 2008. Residual impact of raw and composted poultry litter on soil carbon pools. Electronic Journal of Integrative Biosciences [serial online]. 6:30-40.

Interpretive Summary: Application of animal manures or composts to soils increases some aspects of soil quality. However, there is little information on the duration of these effects after manure or compost applications cease. We showed that soil bulk density was greater in cropping systems fertilized with mineral fertilizers (MF) than in similar cropping systems fertilized with poultry litter (PL) and composted poultry litter (CPL) four years after PL and CPL were last applied even though PL and CPL were applied only two or three times at rates < 4 Mg per ha per application. While there were no differences among cropping systems in total soil carbon and nitrogen or in soil carbon that is readily decomposed by soil microorganisms four years after PL and CPL were last applied, the amount of carbon incorporated into the soil during the years that PL and CPL were applied were positively related to the amount of soil carbon that decomposed at an intermediate rate four years later. Also, the rates of decomposition of soil carbon that decomposed quickly and at intermediate rates were greater in PL than in MF systems and intermediate in CPL systems. Since carbon decomposition rates are generally related to nitrogen decomposition rates, PL applications likely had a positive residual effect on soil nitrogen fertility relative to MF four years after application. We conclude that soil quality benefits of low rate applications of PL and CPL can last up to four years after PL is last applied and that these improvements should be considered when valuing PL and CPL as soil amendments and as sources of fertility.

Technical Abstract: Application of animal manures or composts to soils increases soil carbon levels and improves soil physical properties. However, there is little information on the duration of these effects after manure or compost applications cease. We evaluated the residual effects of applying poultry litter (PL) and composted poultry litter (CPL) at < 4 Mg ha-1 application-1 on soil carbon fractions and other soil properties in low input crop rotations. We sampled soil four years after PL and CPL were last applied in wheat-soybean-corn rotations fertilized with 1) NPK mineral fertilizers (MF) only, 2) PL supplemented with MF, and 3) CPL supplemented with MF. Soil bulk density was greater in MF than in PL and CPL systems compared to initial values (P < 0.10) four years after PL and CPL were last applied. There were no differences among systems in total soil C and N or in active and slow soil C pool sizes four years after PL and CPL were last applied. The size of the slow C pool, however, was positively related to C input levels during the years that PL and CPL were applied, indicating that there was a 4-year residual impact of C inputs on the slow C pool. Also, active and slow C pool rate constants were greater in PL than in MF systems (P < 0.05), averaging 0.2870 and 0.0053 d-1 compared to 0.1103 and 0.0037 d-1, respectively. Rate constants were intermediate in CPL systems, averaging 0.2398 and 0.0045 d-1. Since C mineralization rates are generally correlated with N mineralization rates, PL applications may have had a positive residual effect on soil N fertility relative to MF. We conclude that soil quality benefits of low rate applications of PL and CPL can last up to four years after PL is last applied and that these improvements should be considered when valuing PL and CPL as soil amendments and as sources of fertility.