An 18-year field experiment to assess how various types of organic waste used at European regulatory rates sustain crop yields and C, N, P, and K dynamics in a French calcareous soil
Résumé
Recycling organic waste (OW) in agriculture can improve soil fertility and substitute chemical fertilizers depending on the OW and their treatment. The effects of OW have often been studied in simplified cropping systems to strengthen the observed effects. The objective of this study was thus to evaluate the long-term effects of different types of OW used at European regulatory rates on C storage, crop yields and N, P, and K dynamics. OW has been applied every 2 years at 170 kg N ha-1 since 2001 in the long-term field experiment PROspective in northeastern France on a silty loam calcosol. The 5 types of OW included urban sewage sludge (SLU), green waste and SLU compost (GWS), municipal biowaste compost (BIO), farmyard manure (FYM), and composted FYM (FYMC). The control treatment (CON) did not receive any OW. All treatments were studied after applying (N + ) or not applying (N-) mineral N fertilization at an annual optimal rate. Biowaste digestate was also applied after 2014 in N- treatments. OW application increased crop yield compared with the unfertilized control. Mineral N fertilizer partially substituted by OW allowed crop yield to be sustained compared with mineral fertilizer only, saving 18–54% mineral N fertilizer, 56–80% mineral P fertilizer and 14–76% mineral K fertilizer. No effects on crop grain N, P and K concentrations were found. The efficiency of OW to maintain SOC, total N, Olsen-P and exchangeable K contents in soils greatly varied with the type of OW. Except for SLU, the SOC stocks significantly increased from + 2.9 to + 7.0 t SOC ha-1 for FYMC_N- and BIO_N-, respectively. SLU and digestate had the greatest N fertilizer replacement value (58% and 69%, respectively). N-leaching risk did not increase with OW application in the long term. For a positive
of 100 kg ha-1, Olsen-P increased by 2 mg P kg-1 in the GWS_N- and SLU_N- treatments, whereas Olsen-P decreased in other treatments. A surplus of + 100 kg ha-1
raised the exchangeable K stock by 20 and 21 kg K ha-1 in the FYM_N- and FYMC_N- treatments, respectively, whereas exchangeable K decreased in the BIO and GWS treatments. Our results highlight the ability of all tested types of OW to sustain crop yields in the long term when used at EU regulatory rates, while their effects on mineral fertilizer savings, SOC, soil mineral N, Olsen-P, and exchangeable K contents greatly varied according to the considered OW.