| Purple sloping cropland is an important agricultural resource in the south of China,which is widely distributed in the middle and upper reaches of the Yangtze River,with steep slopes and strong agricultural production activities,damage to farmland soil structure and serious soil erosion.Soil Water Repellency(SWR)exists all over the world,severe SWR will increase surface runoff,causing soil water loss and nutrient loss,reduce soil fertility and crop yields,lead to groundwater pollution and surface pollution.Mild SWR can increase the stability of soil aggregates and nitrogen fixation,reduce soil surface disintegration and stripping,and play a protective role in soil surface layer.Besides,soil water loss and soil structure damage in purple soil sloping cropland can cause SWR changes,however,studies on the changing characteristics of SWR and its influence factors in purple soil areas are rare.In particular,studies on the effects of different fertilization and cultivation practices and typical crops on SWR are rarely reported.Therefore,the study intends to use field monitoring plots to compare and analyze the change characteristics of SWR and other soil physicochemical variables,as well as runoff and sediment yields by setting different fertilization and cultivation measures,and at the same time,obtain the time evolution characteristics of SWR through high frequency sampling of soil during the typical crop growth periods,and reveal the interaction mechanism between it and soil physicochemical variables.This study will further enrich the theory of soil water repellency and provide solid scientific support for the sustainable development of mountain agriculture and environmental protection.In order to explore the effects of different fertilization and cultivation measures on soil water repellency and soil water loss of purple soil slopes,five treatments on sloping cropland in the purple soil were set up:(1)no fertilizer with downslope tillage(CK),(2)combined application of manure and fertilizer with downslope tillage(T1),(3)chemical fertilizers with downslope tillage(T2),(4)chemical fertilizer with increasing fertilization with downslope tillage(T3),and(5)chemical fertilizer with contour tillage(T4),each treatment repeated three times.Taking Chongqing’s local maize"Zhong-Yuan 309"varieties as the test varieties,by measuring SWR,total nitrogen(TN),soil organic carbon(SOC),soil moisture,p H,soil micro-aggregates,runoff and sediment yields over four periods of maize(jointing stage,tasseling stage,filling stage and maturity stage),analyzing and comparing the change characteristics of them,and exploring their coupling relationship.The main results of the study were as follow:(1)The soil was wettable under different fertilization and cultivation measures,and the SWR under T1 treatment was significantly higher than CK and T2 treatment.With the exception of soil moisture content,there were significant(P<0.05)differences in other indicators.The SOC content under T1 treatment and T4 treatment was significantly greater than CK treatment,the TN content under fertilization treatment was higher than CK treatment,and p H was lower than CK treatment under T2 and T3treatment.The proportion of the micro-aggregates in size 1-0.25 mm was lowest under CK treatment,and T4 treatment was highest.The proportions of the micro-aggregates in size 0.25-0.05 mm under T1 and T4 treatment were significantly lower than CK and T2treatment.SWR was highly(P<0.01)significant positively related to TN,and was significant(P<0.05)positive related to SOC content and the proportions of 1-0.25 mm micro-aggregates,but was significant(P<0.05)negative related to the proportions of0.25-0.05 mm micro-aggregates.SWR was not significant(P>0.05)related to p H,soil moisture,the proportions of 0.05-0.01 mm,0.01-0.005 mm,0.005-0.002 mm and<0.002 mm micro-aggregates.It was explained that the combined application of manure and fertilizer is beneficial to enhance SWR,what’s more,the content of TN,SOC and the proportions of 1-0.25 mm micro-aggregates had deep influence on SWR.(2)There was a significant(P<0.05)change in SWR under different growth periods of maize,and the SWR during the jointing stage was significantly stronger than tasseling stage and filling stage.The content of SOC at tasseling stage was(P<0.05)lower than other periods.The soil moisture content increased first and then decreased,with the minimum value at jointing stage and the maximum value at filling stage.The proportion of 0.05-0.01 mm micro-aggregates at tasseling stage was significantly(P<0.05)lower than that at filling stage and maturity stage.The proportions of 0.005-0.002mm micro-aggregates at jointing stage and tasseling stage were significantly(P<0.05)lower than that at filling stage and maturity stage,while the proportions of<0.002 mm micro-aggregates at jointing stage and tasseling stage were significantly(P<0.05)higher than that at filling stage and maturity stage.Besides,the content of TN,the proportions of 1-0.25 mm,0.25-0.05 mm and 0.01-0.005 mm micro-aggregates and p H did not differ significantly(P>0.05)during each growth periods.During the jointing stage,the relationship between SWR and other indicators was not significant(P>0.05).During the tasseling stage,there was an highly(P<0.01)significant positive correlation between TN content,and a significant(P<0.05)positive correlation between SWR and the proportion of 1-0.25 mm micro-aggregates,and a significant(P<0.05)negative correlation between SWR and the proportion of0.25-0.05 mm micro-aggregates(P<0.01).During the filling stage,the relationship between SWR and the contents of TN and SOC at was significantly(P<0.05)positive(P<0.05),and a significant(P<0.05)negative correlation between SWR and the proportions of 0.25-0.05 mm and 0.005-0.002 mm micro-aggregates(P<0.05).And during maturity stage,SWR was highly(P<0.01)significant positively correlated with SOC content,significant(P<0.05)negatively correlated with the proportion of0.05-0.01 mm micro-aggregates,and significant(P<0.05)positively correlated with the proportion of 0.01-0.005 mm micro-aggregates.It showed that there were many factors affecting SWR during the growth period of maize,and more in-depth research is needed to explore their relationship.(3)Under different fertilization and cultivation measures,there are significant(P<0.05)differences in runoff,sediment concentration and sediment yield,and the runoff ranked as CK(3.44 L/m~2)>T3(1.76 L/m~2)>T2(2.50 L/m~2)>T1(1.76 L/m~2)>T4(0.71 L/m2).The sediment concentration ranked as T3(1.76 L/m~2)>T2(2.50 L/m~2)>T1(1.76 L/m~2)>T4(0.71 L/m~2).And the sediment yield ranked as CK(5.62 kg/ha)>T3(2.70 kg/ha)>T2(2.36 kg/ha)>T1(1.43 kg/ha)>T4(0.21 kg/ha).For each treatments,CK treatment had the fastest rate of erosion and T4 treatment was the slowest,which was shown as CK>T3>T2>T1>T4,it showed that contour tillage can effectively reduce soil and water loss,and prevent soil erosion.The average runoff of tasseling stage was greater than that of filling stage,which indicated that the lager SWR in wettable soil could help reduce the runoff. |
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