Long-term combined effects of tillage and rice cultivation with phosphogypsum or farmyard manure on the concentration of salts, minerals, and heavy metals of saline-sodic paddy fields in Northeast China

Authors: HUANG, LIHUA - Chinese Academy Of Sciences; LIU, YING - Jilin University; Ferreira, Jorge; WANG, MINGMING - Chinese Academy Of Sciences; NA, JIA - Chinese Academy Of Sciences; HUANG, JINXIN - Chinese Academy Of Sciences; LIANG, ZHENGWEI - Chinese Academy Of Sciences

Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/3/2021
Publication Date: 10/13/2021
Citation: Huang, L., Liu, Y., Ferreira, J.F.S., Wang, M., Na, J., Huang, J., Liang, Z. 2021. Long-term combined effects of tillage and rice cultivation with phosphogypsum or farmyard manure on the concentration of salts, minerals, and heavy metals of saline-sodic paddy fields in Northeast China. Soil & Tillage Research. 215. Article 105222. https://doi.org/10.1016/j.still.2021.105222.
DOI: https://doi.org/10.1016/j.still.2021.105222

Interpretive Summary: China is the main rice producer in Asia with 209.63 million tons being produced in 2019. Over 90% of this production is obtained from irrigated paddy fields with northeast China provinces, which account for 37.6 million tons, 18% of the national rice yield (https://www.statista.com/statistics/242360/production-of-rice-in-china-by-province/). However, soil salinity and sodicity have become a major ecological problem in northeast China due to poor management of irrigation, overgrown population, and intensive livestock grazing in past years. Rice provides both food security for a growing population and an agricultural approach recommended by the government to reclaim saline-sodic soils into productive fields. However, rice cultivation alone has not solved the issue. Thus, a 10-year field experiment used a combined approach where annual tillage and rice cultivation were combined with either phosphogypsum or locally available farmyard sheep manure compared to undisturbed grassland fields. Both amendments were applied at 25 tons ha-1 once at the onset of the experimental period. Rice paddies were inundated with a groundwater film of approximately 10-cm deep each year. After 10 years, rice cultivation and tillage alone were not enough to significantly reduce soil salinity and sodicity in all soil layers. However, when rice cultivation and tillage were combined with phosphogypsum or farmyard manure, respectively, soil layers had an approximate reduction in soil sodium concentrations of 61.5 and 61%; soil carbonates of 63 and 58%; chloride concentration of 76 and 80%; soil alkalinity (pH) in 1.0 and 1.3 units; and soil electrical conductivity (a main measure of salinity) of 49 and 48%. These amendments also increased soil organic matter, available nitrogen, and available phosphorus significantly. Although both amendments are sources of heavy metals, soil heavy metal concentrations were kept below the environmental quality standards held for Chinese soils. Phosphogypsum and farmyard manure are both locally available and affordable to farmers and can be successfully used to reclaim saline-sodic soils into agriculturally productive soils in China. The knowledge generated in this long-term field research can be applied to large-scale rice cultivation and is important for food security and agricultural production using soils previously colonized by salt-tolerant plants only used for livestock grazing.

Technical Abstract: Soil sodicity is a major ecological problem in the western Songnen Plain of Northeast China and rice cultivation is the main approach used to mitigate saline-sodic soil. However, rice cultivation alone may not be the most effective practice. This study aimed to investigate the combined effects of annual tillage and rice cultivation with either phosphogypsum or farmyard manure on soil salinity, mineral status, and concentration of heavy metals in saline-sodic paddy fields. Treatments were: 1) untreated (no amendments), untilled, and uncultivated (no rice) saline-sodic native grasslands (UG); 2) untreated, tilled, rice-cultivated paddy fields (PFU); 3) tilled, rice-cultivated, amended paddy fields with phosphogypsum (PFPG); and 4) tilled, rice-cultivated, amended paddy fields with farmyard manure (PFFM). The effectiveness of these treatments on soil improvement was evaluated after a 10-year field experiment. Compared to the UG control, the 0-20-cm topsoil layer of PFU, PFPG, PFFM had respective decreases in Na+ concentrations by 42.9%, 61.5%, and 60.9%, in CO32-+HCO3- concentrations by 18.9%, 63.2%, and 57.9%; in Cl- concentration by 64.6%, 75.7%, and 79.9%,; in pH units in 0.57, 1.05, and 1.30 units; in soil electrical conductivity (EC1:5) by 18.3%, 49.1%, and 48.3%; and in exchange sodium percentage (ESP) by 47.2%, 66.9%, and 72.5%. Also, the 0-20-cm topsoil layer of PFPG and PFFM had its concentrations of soil organic matter (SOM), available nitrogen (AN), and available phosphorus (AP) significantly (P<0.05) increased compared to the UG control. However, the concentrations of five heavy metals (As, Pb, Cd, Cr, and Hg) were kept within a safe range in saline-sodic paddy fields amended with phosphogypsum or farmyard manure and were far below the environmental quality standard held for Chinese soils. Therefore, phosphogypsum and farmyard manure significantly decreased soil salinity and sodicity and increased soil fertility and SOM. Because these amendments are locally available and affordable to farmers, their use is deemed suitable for large-scale soil reclamation and the mitigation of salinity and sodicity in soils destined for rice cultivation in Northeast China.