Effect of typical takyr solonetzs reclamation with Flue flue gas desulphurization gypsum and its security assessment

Abstract: Flue gas desulphurization (FGD) gypsum is an industrial waste, which is produced by coal-fired power plant based on limestone-gypsum with a novel wet device. Takyric solonetz, a typical subclass of alkali soil, is widely distributed in the north of Yinchuan Plain of Ningxia Autonomous Region, the west of Hetao Plain and the desert steppe in north Xinjiang in China. Due to the hard soil texture, poor permeability and difficult improvement, takyric solonetz has become the main factor severely affecting the development of local agriculture, and is expected to bring threat to the regional food security in the future. The present study was to evaluate the feasibility and effectiveness of FGD gypsum on improving the typical takyr solonetzs of Ningxia region. In 2013 and 2014, a comparative field experiment was conducted in the farmland of Qianjin Farm in Pingluo County, Ningxia region, China (106°13′-106°26′E, 38°45′-38°55′N) and the precocious japonica "Jite 605" was taken as the test material. Five application rates of FGD gypsum (0, 1.05×104, 2.10×104, 3.15×104 and 4.20×104 kg/hm2) were applied. Besides, the leaching amount (4.5×103 m3/hm2) was designed in combination with FGD gypsum. We investigated the changes in soil property and agricultural production as well as the safety of FGD gypsum as soil amendment. It showed that by using FGD gypsum stimulation, the soil pH value and ESP (exchangeable sodium percentage) decreased in the 0-20 cm soil layer, which were from 9.8 and 42.1% before experiment to 9.1 and 35.2% in 2013, and 8.3 and 25.7% after experiment in 2014, respectively. These changes facilitated the growth of rice, and thereby increased the rice yield and improved the quality of the plots treated with FGD gypsum. The rice yield increased by 2 333.3-3 317.4 kg/hm2. The amount of FGD gypsum used did not change much the rice grain weight, the milled rice, the brown rice rate and the chalky rate, while the head milled rice rate increased from 52.6% to 59.7%; the chalky grain rate and chalkiness degree were changed by the varying of the amount of FGD gypsum: it decreased from a peak value of 9.3% at 3.15×104 kg/hm2 FGD gypsum to 8.1% at first, and then increased gradually to 9.1%. The amount of FGD gypsum improved the appearance quality of rice, chalky rice rate but reduced the cooking quality of gel consistency. The results showed that the suitable amount of FGD gypsum applied to reclaim takyric solonetz farmlands and improve rice quality was 3.15×104 kg/hm2, which had obvious effect. The contents of metals i.e. chromium (Cr), arsenic (As), cadmium (Cd), mercury (Hg) and lead (Pb) in corn grains were quantified by the inductively coupled plasma mass spectrometry (ICP-MS). Comparing the metal contents in grains, when 3.15×104 kg/hm2 FGD gypsum was applied to cultivated paddy, the contents of almost all of the metals in the corn grains in the FGD gypsum-treated plots were the same to or lower than those in the control plot. Almost all of the metal contents were lower than the standard values set by pharmacopoeias for human intake. These results suggest that the proper use of FGD gypsum will be helpful to fertilize the soil, and thereby increase the production and improve rice quality. Moreover, the contents of the heavy metals in the soils well comply with the Hygienic Standard for Grains in China (GB/T2715-2005), which implies that FGD gypsum will not deteriorate the soil environmental quality. The findings of this study will provide technical support for improving the newly reclaimed takyric solonetz farmlands as well as data support for improving the rice quality.