| With the demand for grain and food constantly growing, water and soil loss and soil degradation for farmland resource used by depletion-type and high strength utilization, fertilizer of inputting farmland is increasing year by year, which leads to increasingly intensifying of water environment deterioration for agricultural non-point pollution (especially nitrogen and phosphorus).Therefore, exploring prevention and controlling measures of agricultural non-point pollution has been paid more attention to one of environmental problems. Farmland nitrogen and phosphorus loss mainly enter the water through runoff and soil. However, hedgerow technique, for its the roles such as mechanical block, not only effectively conserve water and soil, but also significantly reduce potential hazards of water eutrophication for the loss of nitrogen and phosphorus. At present, researches on effect of hedgerows on controlling farmland nitrogen and phosphorus loss mostly involved reducing amount of total nitrogen and phosphorus or runoff total nitrogen and phosphorus loss in analyzing conservation water and soil. Effect of plant absorbing and soil storing nitrogen and phosphorus is hardly studied; Reason of hedgerow on controlling nitrogen and phosphorus is hardly discussed. Researches on evaluating of comprehensive ecological benefits for hedgerow patterns mostly focus on benefits of conservation water and soil and improving land productivity. Benefit of controlling agricultural non-point pollution is neglected. Therefore, taking with slope farmland in upstream and surrounding of the Three Gorges Reservoir purple hilly region as the objective of research, effect of hedgerow-crop patterns on controlling nitrogen and phosphorus loss and its response to soil comprehensive anti-erodibility were studied by runoff plot experiment, laboratory analysis and mathematical statistics, and comprehensive ecological benefits of hedgerow-crop patterns were evaluated by multi-factor assessment, in this paper. Main results are as follows.1. Effect of hedgerow-crop patterns on controlling nitrogen loss in slope farmlandHedgerow patterns could reduce concentration of runoff total N and different form runoff N. In terms of runoff total N concentration, in Fuling experimental zone, compared with conventional contour crop pattern (T4), average concentration of runoff total N decreased by26.2%,27.5%,13.5%for Hemerocallis citrina baroni hedgerow pattern (T1), Honeysuckle hedgerow pattern (T2), two stripe contour Mulberry hedgerow pattern(T3), respectively; runoff N concentration under three stripe contour Mulberry hedgerow pattern(T5) and border mulberry pattern(T6) had no decreasing trend during experiment. In Ziyang experimental zone, compared with conventional contour cropping pattern (T7), average concentration of runoff total N decreased by36.0%,33.0%for Amorpha hedgerow pattern (T8) and Vetiver hedgerow pattern (T9) in20°slope farmland, respectively; Compared with conventional contour crop pattern (T10), average concentration of runoff total N decreased by5.9%for Alfalfa pattern(T11), and that of Eulaliopsis binata pattern(T12) had no significant decreasing trend, in13°slope farmland. Therefore, the order of effect of different hedgerow patterns on decreasing runoff nitrogen concentration was T2>T1>T3in Fuling, T8>T9in20°slope farmland of Ziyang, T11>T12in13°one. Hedgerow-crop patterns reduced amount of total N and different form N loss. In terms of amount of total N, in Fuling experimental zone, compared with T4, amount of total N loss under T1,T2and T3reduced7.34kg/hm2,6.54kg/hm2,1.78kg/hm2, and their reduction ratio were34.9%,31.0%,8.4%from2011to2012, respectively; That of T5and T6had no decreasing trend during experiment. In Ziyang experimental zone, compared with T7, amount of total N loss under T8and T9reduced217.33kg/hm2,95.75kg/hm2, and their reduction ratio were92.4%,90.0%from2010to2013in20°slope farmland, respectively; That of T11and T12reduced82.65kg/hm2,78.12kg/hm2, and their reduction ratio were88.7%,83.9%in13°slope farmland, respectively. Therefore, the order of effect of different hedgerow patterns on controlling nitrogen loss was T1>T2>T3in Fuling, T8>T9in20°slope farmland of Ziyang, T11>T12in13°one.2. Effect of hedgerow-crop patterns on controlling phosphorus loss in slope farmlandHedgerow patterns could reduce concentration of runoff total P and different form runoff P. In terms of runoff total P concentration, in Fuling experimental zone, compared with T4, average concentration of runoff total P decreased by38.1%,44.1%,41.9%,4.3%for T1, T2, T3, T4, respectively; runoff P concentration under T6had no decreasing trend during experiment. In Ziyang experimental zone, compared with T7, average concentration of runoff total P decreased by52.6%,42.1%for T8and T9in20°slope farmland, respectively; Compared with T10, average concentration of runoff total P decreased by40.4%,41.3%for T11, T12in13°slope farmland, respectively. Therefore, the order of effect of different hedgerow patterns on decreasing runoff phosphorus concentration was T2>T3>T1>T5in Fuling, T8>T9in20°slope farmland of Ziyang, T11≈T12for13°one.Hedgerow patterns reduced amount of total P and different form P loss, too. In terms of amount of total P, in Fuling experimental zone, compared with T4, amount of total N loss under T1,T2and T3reduced0.99kg/hm2,1.22kg/hm2,0.84kg/hm2, and their reduction ratio were38.4%,47.4%,32.7%from2011to2012, respectively; That of T5and T6also had no decreasing trend during experiment. In Ziyang experimental zone, compared with T7, amount of total N loss under T8and T9reduced53.91kg/hm2,51.39kg/hm2, and their reduction ratio were96.1%,91.6%from2010to2012in20°slope farmland, respectively; compared with T10, that of T11and T12reduced48.81kg/hm2,48.09kg/hm2, and their reduction ratio was reduced by94.0%,92.7%from2010to2012in13°slope farmland, respectively. Therefore, the order of effect of different hedgerow patterns on controlling phosphorus loss was T1>T2>T3in Fuling, T8>T9in20°slope farmland of Ziyang, T11>T12in13°one.3. Effect of plant absorbing and soil storing nitrogen and phosphorus under hedgerow-crop patternsHedgerow-crop patterns increased plant (including crops and hedgerows) absorbing and soil storing the amount of nitrogen and phosphorus. Relative absorption rates of plant absorbing N and P were1.6-30.0%,2.0-16.0%(except for Hemerocallis citrina baroni pattern) under hedgerow patterns, respectively; Relative storage rates of soil storing N and P were7.5-25.8%,9.7～50.9%, respectively. Therefore, it was called by plant absorbing and soil storing effect of hedgerow-crop patterns on controlling N and P loss that hedgerow-crop patterns increased amount of plant absorbing and soil storing N and P in this paper.Effect of plant absorbing and soil storing N and P under different hedgerows was different for the difference of their biological and physiological characteristics. On this research conditions, the order of the effect of plant absorbing N under different hedgerow patterns was Honeysuckle> mulberry>Hemerocallis citrina baroni in Fuling, Amorpha> Vetiver in20°slope farmland of Ziyang, Alfalfa> Eulaliopsis binat in13°one; The order of the effect of plant absorbing P was Honeysuckle> mulberry in Fuling, Vetiver>Amorpha in20°slope farmland of Ziyang, Alfalfa> Eulaliopsis binat in13°one. In Fuling experimental zone, the order of effect of soil storing N under different hedgerow patterns was Hemerocallis citrina baroni> Honeysuckle> mulberry, the order of effect of soil storing P was Hemerocallis citrina baroni> mulberry> Honeysuckle. In Ziyang experimental zone, the order of effect of soil storing N and P was Amorpha> Vetiver in20°slope farmland, Alfalfa> Eulaliopsis binat in13°one.4. Soil comprehensive anti-erodibility and their influence on amount of nitrogen and phosphorus loss under hedgerow-crop patternsIn Ziyang experimental zone, Soil shear strength (SS), anti-erodibility(AE), anti-scouring(AS) and comprehensive anti-erodibility(CAE) of hedgerow-crop patterns were higher than those of conventional contour crop one. In20°slope farmland, surface soil SS, AEI, ASI and CAEI for T8increased by70.3%,3.99,84.1%,102.9%, respectively, and those of T9increased by49.6%,2.65,49.0%,91.9%, respectively. In13°slope farmland, surface soil SS, AEI, ASI and CAEI for T11increased by62.2%,3.13,188.3%、87.9%, respectively, and those of T12were increased by89.7%,2.36,174.8%,82.9%, respectively. Therefore, In terms of CAE, the order of effect of different hedgerow-crop patterns improved CAE was Amorpha> Vetiver in20°slope farmland, Alfalfa> Eulaliopsis binat in13°one.Compared with conventional contour crop pattern, hedgerow and crop belt SS, AE, AS and CAE of slope farmland in each slope position were improved under hedgerow-crop patterns, especially hedgerow belt. Hedgerow-crop patterns weaken considerably the conditions that values of soil anti-erosion indexes decreasing by nearly line or rapidly decreasing from low slope to top slop, and improved excessive slope heterogeneity of soil anti-erosion indexes in slope farmland.Amount of slope farmland total N and P loss decreased by exponential or linear function with increasing of SS, AEI, ASI and CAEI values, and values of adjusted determination coefficient (R2) of fitting equation for between SS, ASI, CAEI values and amount of slope farmland total N and P loss reached extremely significant level. Therefore, it was inferred that effect of hedgerow-crop patterns on controlling N and P loss should increased with improving of SS, SAI and CSAI.5. Evaluating of comprehensive ecological benefits for hedgerow-crop patternsIn20°slope farmland of Ziyang, compared with T7, indexes of comprehensive ecological effect(A), soil and water conservation one(B1), controlling agricultural non-point source pollutant one (B2), increasing soil anti-erosion force one (B3) and improving land productivity one (B4) for T8were increased by301.9%,278.4%,346.6%,107.2%,23.6%, respectively, and those of T9were increased by288.1%,262.6%,333.9%,93.7%,25.3%, respectively. In13°slope farmland, compared with T10, indexes of A, B1, B2, B3and B4for T11were increased by215.6%,237.5%,220.2%,126.0%,33.6%, respectively, and those of T12were increased by206.4%,228.6%,212.6%,106.3%,35.8%, respectively. The order of index of different type ecological effect was B2(1.165)>B1(0.962)>B4(0.495)>B3(0.332) under hedgerow-crop patterns. Therefore, Hedgerow-crop patterns improved comprehensive and different type ecological benefits of slope farmland. The order of effect of different hedgerow-crop patterns improving ecological benefits was Amorpha> Vetiver in20°slope farmland, Alfalfa> Eulaliopsis binat in13°one. If shrub hedgerow patterns be carry out in slope farmland of southwest purple hilly area, especially lager than15°slope farmland, better comprehensive ecological benefit can be obtain.Overall, hedgerow-crop patterns could be effectively controlling nitrogen and phosphorus loss of slope farmland, increase plant absorbing and soil storing the amount of nitrogen and phosphorus, improve ecological benefit, which is extremely important theoretical and practical significance to protect water environmental quality of Three Gorges Reservoir and its small watershed in upstream region. Hedgerow-crop patterns can be used as source controlling technology of controlling agricultural non-point pollutants nitrogen and phosphorus. In this paper, relative absorption rate of plant absorbing N and P, relative storage rate of soil storing N and P was introduced, and they may characterized plant absorbing and soil storing effect of hedgerow-crop patterns controlling N and P loss, respectively; Relational model between the amount of total N and P loss and soil anti-erosion indexes was established; Evaluation index system including indexs of hedgerow patterns controlling agricultural non-point pollution of comprehensive ecological benefits under hedgerow-crop patterns was established. However, in this paper, effect of N and P loss for hedgerow-crop patterns controlling interflow isn’t studied; the economic and social benefits aren’t evaluated. Therefore, effect of N and P loss for hedgerow-crop patterns controlling interflow should be further studied from now on; Index system of evaluating social, landscape and comprehensive benefits under hedgerow-crop patterns should be reasonably established. |
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