Improvement Of Two Acidic Soils By Calcium-Montmorillonite And Lime

It is estimated that the acid soil area in the world accounts for about 40%-50%of the potential arable land.And about one-fifth of China's cultivated soil has been aged to acidic soils.The improvement of acid soil is of great significance to crop growth,ecological environment and human health.Soil acidification is known to be a natural and slow process along with clay mineral weathering.In recent years however,with intensive soil utilization in agriculture,soil acidification has increased dramatically and nitrification of ammonium nitrogen fertilizer is one of the main contributors to soil acidification.The research on the improvement of acidic soil has been mainly from the perspective of increasing soil nutrients or neutralizing acid,rather than the nature of the soil.Lime is the traditional application to improve acidic soils but it often makes the soil acidic again leading to soil compaction in most cases.Montmorillonite is the main clay mineral component of alkaline or neutral soils,more so it is known to undergo further weathering processes during soil acidification.In this study,from the perspective of soil clay minerals,indoor simulation experiments and outdoor pot experiments were designed to conduct comparative tests between traditional improvers and clay mineral amendments.The use of laboratory-based incubations was used in this study,and nitrification was measured while kinetic curves were fitted to check the effects of decreasing soil acidity by calcium hydroxide?Ca-OH?and calcium-montmorillonite?Ca-Mont?on nitrification of this acidic soil.Through a one-year outdoor pot experiment,calcium-montmorillonite Ca-Mont)and calcium carbonate?Ca-CO₃?were added to acidic purple soil and red soil,respectively,to plant Chinese cabbages four times,and the effects of different types of amendments on crop yield and soil properties were determined and compared.The results of indoor simulation experiments showed that significant nitrification was observed both in Ca-OH and Ca-Mont treatments,and the nitrification process was fitted in the first-order kinetic model,N_NO3=N₀+N_p?1-exp?-k₁t???P<0.001?.The net nitrification rate of Ca-OH treatment(3.43 mg N·kg^-1·d^-1)was significantly higher than that of Ca-Mont treatment(2.38 mg N·kg^-1·d^-1).The potential nitrification rate?V_p?were6.42,8.58 mg N·kg^-1·day^-1 at pH 5.7 and 6.2 respectively,and the average nitrification rate?V_a?of Ca-OH treatment were 2.71,3.88 mg N·kg^-1·day^-1 respectively,which were significantly greater than those of Ca–Mont treatment(V_p were 3.40,4.56 mg N·kg^-1·day^-1 and V_a were 2.36,3.04 mg N·kg^-1·day^-1 at pH 5.7 and 6.2 respectively).Therefore the net nitrification rate,potential nitrification rate?V_p?and average nitrification rate?V_a?of Ca-OH treatment were significantly higher than that of Ca-Mont treatment,suggesting that the possibility and degree of soil reacidification by using lime to improve acidic soil is greater than using calcium montmorillonite.The results of outdoor pot experiments showed:1)Adding calcium-montmorillonite?Ca-Mont?and calcium carbonate?Ca-CO₃?modifiers to the acid purple soil and red soil,respectively,could increase soil pH and reduce soil exchangeable acid?EA?and exchangeable aluminum?EAl?content.In contrast,Ca-Mont treatment in increasing pH was not as effective as calcium carbonate did in acidic soils?purple soil and red soil?.In the calcium carbonate group,the pH increased to above 6 at the end of the first planting,and it was found in purple soil and red soil.However,after one year,the Ca-CO₃ treatment also showed a greater decrease in pH,with a decrease of 0.7 and 1.3 units in purple soil and red soil,respectively;while the Ca-Mont group decreased by 0.3 and 0.9 units,respectively.In both acidic soils,the EA content of Ca-CO₃ group was below 2.0 mmol·kg-1,while the EA content of Ca-Mont group was significantly higher than that of Ca-CO₃ group,and the change trend was different in the two soils.During the one-year pot experiment,the EA content in the Ca-CO₃ group in the purple soil showed an upward trend in the later period,with a increased of 53.57%;while the Ca-Mont treatment continued to slowly decrease,with a decrease of 25.37%.But the effect was not obvious in red soil.Even the EA in the Ca-Mont group had an increasing trend,and the exchangeable hydrogen was mainly increased by about50%.Acidic soil acidity decreased slowly when not grown?Fallow Control group?,but the acidity of acidic soils will increase?purple soil?or show an increase trend?red soil?.2)The application of calcium-montmorillonite?Ca-Mont?and calcium carbonate?Ca-CO₃?in acid soil increased the yield of crops in different degrees.The yields of calcium carbonate treatment in purple soil and red soil were 110.26 g and 37.30 g,respectively.Calcium-montmorillonite treatment was 66.22 g and 33.00 g,respectively.And the output of calcium carbonate treatment in both acidic soils was better than that of montmorillonite treatment,but it was higher in calcium-montmorillonite treatment in the last three cultivations,especially in acidic red soil,even two times the calcium carbonate group.Dry weight had a similar trend.From the perspective of four plantings,Ca-CO₃treatment in the two acidic soils had a significantly higher pH-elevation effect than Ca-Mont,but as the planting time prolonged,the soil of Ca-Mont treatment group was effective for the growth of Chinese cabbage,both were better than that of the Ca-CO₃treatment group.3)The application of calcium-montmorillonite?Ca-Mont?and calcium carbonate?Ca-CO₃?increased the cation exchange capacity?CEC?content and the base saturation?BS%?both in acid purple soil and red soil.In the two acidic soils,the cation exchange capacity of calcium-montmorillonite soil was above 15.4 cmol·kg^-1,while the content of CEC in calcium carbonate soil was between 6.2 cmol·kg^-1 and 15.4 cmol·kg^-1,and the former was significant higher than the latter.However,its base saturation was opposite,that was,calcium carbonate treatment soil?above 95%?is significantly higher than calcium-montmorillonite treatment?90%⁹5%?,indicating that the calcium carbonate treatment soil wass more sensitive to acidification in both acidic soils.4)Compared with the Fallow Control treatment,the Chinese cabbage planting?Blank Control,Ca-Mont,Ca-CO₃?process increased soil nitrification potential.As a kind of clay mineral,calcium-montmorillonite not only improved the soil structure and soil fertility.At the same time,after one year of pot experiment,the nitrification potential of Ca-Mont treatment was only half that of Ca-CO₃ treatment.The nitrification potential of calcium carbonate treatment in acid purple soil and red soil was stronger than that of calcium-montmorillonite.Indicated that Ca-CO₃ treatment soil was more easily acidified,which was consistent with the results of indoor simulation experiments.In one word,the study showed that the clay mineral modifier,calcium-montmorillonite practical effect was better than that of the inorganic chemical material,calcium carbonate,and the acid return ability of calcium-montmorillonite treatment was also weaker than that of the lime treatment.It was in order to provide a new reference for the improvement of acidic soil.