Striking a balance between N sources: mitigating soil acidification and accumulation of phosphorous and heavy metals from manure

Authors: CAI, ZEIJIANG - Chinese Academy Of Sciences; WANG, BOREN - Chinese Academy Of Agricultural Sciences; ZHANG, LU - Chinese Academy Of Agricultural Sciences; WEN, SHILIN - Chinese Academy Of Agricultural Sciences; XU, MINGGANG - Chinese Academy Of Agricultural Sciences; CARSWELL, ALLISON - Rothamsted Research; Gao, Suduan

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/2/2020
Publication Date: 9/7/2020
Citation: Cai, Z., Wang, B., Zhang, L., Wen, S., Xu, M., Carswell, A.M., Gao, S. 2020. Striking a balance between N sources: mitigating soil acidification and accumulation of phosphorous and heavy metals from manure. Science of the Total Environment. 754. Article 142189. https://doi.org/10.1016/j.scitotenv.2020.142189.
DOI: https://doi.org/10.1016/j.scitotenv.2020.142189

Interpretive Summary: Soil acidification caused by large and continuous input of chemical nitrogen fertilizers has become a factor for limiting plant growth and manure amendment has shown the success to mitigate the problem, but potential accumulation of some nutrients or heavy metals are unknown. This research investigated impact of long-term manure amendment affected nutrient balance and heavy metal accumulation in soil based on a 9-year field study for maize production in an acidic red soil, southern China, and discussed how manure amendment can be managed to balance nutrient supply, prevent soil from acidification, and avoid accumulation of heavy metals. The research found that the amount of manure providing 40% or higher of total nitrogen supply prevented or reversed soil acidification. There is a high potential to use 20% of total nitrogen supply from manure to achieve the same outcome by increasing use efficiency and reducing total nitrogen input. The manure provided all plant needs for phosphorus, but not K, suggesting no chemical phosphorus fertilizers is needed but substantial K input from chemical fertilizers is necessary for crop production. There was a significant accumulation of heavy metal Pb, Cu, and Zn and source reduction by reducing their concentrations in animal feed would be the most effective way to minimize soil contamination and essential for sustainable use of manure in both soil acidity and nutrient management. Findings from this research are directly applicable to acidic soils around the world and also valuable for management of all soil types to improve sustainability of crop production systems.

Technical Abstract: Manure amendment has been shown to effectively prevent red soil (Ferralic Cambisol) acidification from chemical (synthetic) nitrogen (N) fertilization. However, information is lacking on how much manure is needed to mitigate acidification and maintain soil productivity while preventing accumulation of other nutrients and heavy metals from long-term inputs. This study determined the effects of various combinations of manure with urea-N on acidification and changes in soil P, K, and heavy metals in a 9-year maize field experiment in southern China. Treatments included chemical N, P and K fertilization only (NPKM0), and NPK plus swine manure that supplied 20% (NPKM20), 40% (NPKM40), and 60% (NPKM60) of total N at 225 kg N ha-1 year-1. Soil pH, exchangeable acidity, available P and K, and maize yield were determined annually from 2009 to 2018. Soil exchangeable base cations, total and phytoavailable Cr, Pb, As, Ni, Cd, Cu, and Zn were measured in 2018. While NPKM0 and NPKM20 resulted in significant decrease in soil pH from initial 4.93 to 4.46 and 4.71, respectively, NPKM40 and NPKM60 resulted in no change or a significant increase in soil pH (to 5.47), increased exchangeable base cations, and achieved the highest yield. Manure application markedly increased soil available P (but not K) to 67.6-182.6 mg kg-1 and also significantly increased total Pb, Cu, and Zn and available Cu and Zn in soil. The results indicate that 40% or higher of total N sourced manure can prevent or reverse acidification of red soil, provide all P, but need substantial K inputs from chemical fertilizers to balance nutrient supply for plants. An integrated approach by increasing N use efficiency, reducing chemical input, and reducing heavy metal concentrations in animal feed are all necessary for sustainable use of manure in soil acidity and nutrient management as well as minimizing environmental risks.