| Soil erosion is an important environmental problem,and caused agricultural non-point source pollution which has become the largest source of water environmental pollution in the world.Runoff is not only the main driving force of agricultural non-point source pollution but also the driving force and transportation carrier of soil nutrient losses.The proportion of various nutrients in water body may be unbalanced after soil nutrients entering water along with runoff,thus causing changes in the biogeochemical cycling process of water.The usual result is deterioration of water quality and gradual eutrophication of the water body.At the same time,the imbalance of soil nutrient element proportions because of nutrient losses also directly affect the nutrient absorption efficiency of crops,thus affecting the crops' growth and yield.Ecological stoichiometry is a science that studies the equilibrium relationships and interactions of various chemical elements(mainly C,N and P)in ecosystem.However,at present,few studies have explored the characteristics of carbon(C),nitrogen(N)and phosphorus(P)ecological stoichiometry in crops,soil and runoff based on the ecological stoichiometry,and revealed the coupling relationship between them.In addition,studies show that different agronomic measures have different influence on crop nutrient absorption efficiency,soil nutrient accumulation and soil erosion,but studies on their influence on the stoichiometry characteristics of C,N and P in crops,soil and runoff and their relationships are even less.Purple soil is an important soil type,which is shallow,loose and prone to soil erosion.Therefore,exploring the C,N,P stoichiometry characteristics of runoff-soil-crop system in purple soil sloping cropland under different agronomic measures is helpful to understand C,N,P losses mechanism of farmland system and its relationship with agricultural non-point source pollution under fertilization and cultivation measures,and provides new ideas for controlling regional agricultural non-point source pollution.This study was carried out in field monitoring plots of different agronomic measures in the soil and water conservation test site of Houshan Farm,Southwest University.The local maize variety "Zhongnuo309" in Chongqing was used to carry out the field crop,soil and runoff positioning monitoring test.5 treatments(3 replications for each treatment)were used: no fertilizer with downslope cultivation(CK),combined application of manure and fertilizer with downslope cultivation(T1),chemical fertilizers with downslope cultivation(T2),chemical fertilizer with increasingfertilization with downslope cultivation(T3),and chemical fertilizer with contour cultivation(T4).The carbon(C),nitrogen(N)and phosphorus(P)contents of runoff,soil of 0-10 cm and 10-20 cm,and corn in each plot at different growth stages of corn(seedling stage,jointing stage,heading stage and mature stage)were measured,the stoichiometry characterisitics of C,N and P in runoff,soil and corn were compared and analyzed,and the coupling relationship between them was explored.Main conclusions were as follows:(1)There were significant differences in runoff,C,N and P losses of runoff under different agronomic measures and maize growth periods in purple soil sloping cropland(P<0.05).The runoff of CK was the largest,while that of T4 and T1 were smaller.With the development of maize growth periods,the runoff gradually increased.C,N and P losses of T3 were largest,while that of T4 and T2 were smaller under different agronomic measures.With the development of maize growth period,the losses of C and N increased first and then decreased,with the maximum value at heading stage and the minimum value at seedling stage.P loss gradually increases.There was no significant difference in C:N,N:P of runoff between different agronomic measures and different growth periods of maize(P>0.05).C:N was the largest in T1(30.34)and N:P was the largest in CK(31.21).With the development of maize growth period,C:N of runoff decreased first and then increased,reaching the highest at maturity(33.88),N:P increased first and then decreased,reaching the highest at heading stage(41.63).The results showed that combined application of manure and fertilizer and contour cultivation were beneficial to reduce the nutrient losses of runoff in purple soil sloping cropland.N:P of runoff was mainly affected by phosphorus.(2)There were significant differences in the responses of soil physical and chemical properties and stoichiometric characteristics to soil layers,agronomic measures and maize growth periods(P<0.05).With the deepening of the soil layer,the bulk density of the soil gradually increased,and the contents of organic C,total N and total P gradually decreased.Under different agronomic measures,the bulk density was CK>T2>T4>T3>T1,and the water contents was T1>T2>T3>T4>CK.The C,N and P contents in fertilization treatment were higher than those in CK,and the contents were higher in T1 and T4.Only the C:N of T4 and the N:P of T1 were higher than CK.With the development of maize growth periods,the bulk density of soil gradually decreased,the water content decreased first and then increased,and the contents of C,N and P decreased first and then increased,with the maximum value at seedling stage and theminimum value at heading stage.With the development of maize growth periods,soil C:N gradually increased,C:P first increased and then decreased,the maximum value was at jointing stage(26.89),the minimum value was at seedling stage(23.60),soil N:P first increased and then decreased,the maximum value was at jointing stage(2.31),and the minimum value was at maturity stage(2.07).This showed that combined application of manure and fertilizer could significantly improve the C,N and P contents of sloping farmland in purple soil,and could effectively alleviate the N deficiency in this area.(3)The C,N,P contents and their stoichiometric characteristics of maize under different agronomic measures and growth periods were significantly different(P<0.05).The C,N and P contents of maize in fertilized treatments were higher than those in control treatment,and those of T1 treatment was the highest.The C:N,C:P and N:P of maize in fertilized treatments were lower than those of control,C:N and C:P were the lowest at T1,57.66 and 299.77 respectively,and N:P was the lowest at T3(5.18).With the development of maize growth periods,the content of C in maize increased first and then decreased and then increased,while the content of P and N increased first and then decreased,which were the highest at jointing and heading stages.With the development of maize growth periods,maize's C:N showed an increasing trend,and C:P,N:P decreased first and then increased.The results showed that the contents of C,N and P and their stoichiometric ratio were affected by fertilization,growth period,climate,soil,planting system and their own characteristics.(4)The correlation of C,N and P stoichiometric characteristics of runoff,soil and crops in different growth periods of maize was not significant(P>0.05).Except the seedling stage,the soil C:N,N:P in other maize growth stages were negatively correlated with the runoff C:N,N: P.Soil C:N,C:P,N:P at jointing stage and maturity stage were positively correlated with crop C:N,C:P,N: P.C:N,N:P of runoff at jointing stage and maturity stage were positively correlated with C:N,N:P of crops.This showed that the C,N and P-stoichiometric ratios of runoff,soil and crops were affected by many factors.More research is needed to explore the reasons that affect their stoichiometric ratios and their relationships. |
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