Effects Of Sewage Irrigation On The Alfalfa Growth, Quality And Some Soil Physical And Chemical Properties

Pot experiments were conducted to study the effects of different irrigation methods using sewage and reclaimed water on the Alfalfa's growth, quality and soil environment. Seven treatments were set up: fresh water(Q) irrigation, sewage(W) irrigation, reclaimed(Z) water irrigation, sewage mixed (W+Q) and rotational (W/Q) irrigation with fresh water and reclaimed water mixed (Z+Q) and rotational (Z/Q) irrigation with fresh water.The results indicated that sewage and reclaimed water increased stem length and yield compared with fresh water, but inhibited Alfalfa leaf area in early irrigation. Sewage irrigation also inhibited Alfalfa root growth. Effects of irrigation water quality treatments on Alfalfa K content was not remarkable at the first clipping, but W and Z irrigation showed higher K content than Q irrigation by 33.05% and 40.68% at the second clipping, and by 12.90% and 23.39% at the third clipping. Compared with Q irrigation, W and Z irrigation significantly increased Alfalfa Ca contents at the first clipping, however at the second and third clipping, W and Z irrigation treatments were lower than Q irrigation in Alfalfa Ca contents. The three reclaimed water treatments (Z, Z+Q and Z/Q) restrained alfalfa's Fe content, and the sewage treatments(W, W+Q, W/Q) promoted the absorption of Fe at the first, but then inhabited; sewage and reclaimed water irrigation increased Cu content of alfalfa.W and Z irrigation were disadvantageous to the alfalfa's soluble sugar accumulation, but using mixed and rotational irrigation methods increased soluble sugar contents significantly; Pb content in alfalfa was significantly increased under W irrigation , though Z irrigation promoted accumulation of Pb,there was no obvious difference between Z and Q irrigation; The six sewage and reclaimed water treatments(W, Z, W+Q,W/Q,Z+QZ/Q) caused alfalfa Cd accumulation compared with Q irrigation, and the accumulation degree under three sewage treatments was more severe than the three reclaimed water treatments. Although sewage and reclaimed water irrigation caused Pb, Cd accumulation, Pb and Cd contents in Alfalfa were lower thancontamination threshold of National Sanitation Standard (GB 13078-2001).Compared with fresh water (Q) irrigation, sewage (W) and reclaimedwater (Z)irrigation decreased soil pH and increased soil EC , and the influenceof W irrigation was more effective than Z irrigation. Effect of irrigation waterquality treatments on soil inorganic nitrogen was not obvious at the firstclipping, but compared with Q irrigation, W and Z irrigation increased soilinorganic nitrogen contents by 63.59 and 35.02% at the second clipping, andincreased by 82.18% and 30.72% at the third clipping. W irrigationsignificantly increased Pb contents of soil at the third clipping. In threeclippings, the difference between three reclaimed water (Z, Z+Q and Z/Q)irrigation and Q irrigation was not significant. Compared with Q irrigation, Wirrigation increased soil Cd contents in three clippings by 33%, 117.65% and138.89% and Z irrigation increased by 13.33%, 64.71% and 61.11%.Evaluation of heavy metal pollution in soils indicated that during theexperiment, all treatments didn't cause soil pollution by Pb, but soil waspolluted by Cd under sewage irrigation. Accordingly, sewage shouldn't beused for irrigation, but after mixed or rotational with fresh water, it canproperly decrease the adverse effects; reclaimed water can be used as a sourceof irrigation in Alfalfa growth for a short period of time and their long-termeffect should be concerned.