| Field experiment was conducted in Cheng Zhuang station of JingTai County to investigate the effects of irrigation and phosphorus on crop yields and physiological characters and wheat seed quality in wheat-maize-potato intercropping system in 2002-2003. Formulating field condition accordingly,tube simulated experiment was conducted by using the 30cm dia-meter PVC tube to investigate the effect of water-fertilizer coupling on crop yield and physiological and ecological character in wheat-maize intercropping system. In the net house of Gansu Agricultural University in 2003. The results were showed below:1. Irrigation and phosphorus application have significant effect on crop physiological characters in intercropping system. Under the treatment of middle irrigation (W2: 1050m3 /hm2) and high phosphorus (P2: 150 kg P2O5 / hm2), crops in wheat-maize-potato system have the tendency to keep leaf chlorophyll content and root dry weight high, to maintain leaf water status well and to adjust the root/shoot ratio to the optimum value, which contributed to high grain yield .The root grew deeper and the crop yield increased with light water deficit. Under the condition of serious water deficit, both fresh root weight and root oxidation-reduction activity reduced significant-ly while the relative penetrability of cell membrane of root and leaf increased obviously. The result was also indicated that phosphorus have high positive effect on root oxidation-reduction activity, root fresh weight and root length, which conduced to the yield increase. As opposed to no phosphorus treatment, phosphorus supply increased root oxi-dation-reduction activity of wheat and maize by 65.90% and 65.50% in the range of 0-30cm layers, respectively. In phosphorus supply, the fresh root weight of wheat and maize also enhanced by 94.66% and 67.67%. Supply, and the relative penetrability of cell membrane of wheat root ,wheat leaf ,maize root and maize leaf decreased by 7.96 % ,8.33%,2.50 %and 1.62 %, respectively.2. Crop water consumption was significantly changed with the variety of irrigation and phosphorus put into experiment plot. Water comsuption (ET)of wheat,maize and potato under the high-irrigation treatment (W3) was repectively 29.86%,63.01% and 46.38%higher than those under the low-irrigation treatment and respectively 16.17%,24.20% and 28.52% than those under the mid-irrigation treatment(W2) . The result was also found that c rops consumed more water under mid-(Pi)and high-phosphorus(P2) conditions than no-phosphrous(Po) in wheat-maize-potato system .Compared with the (Po), wheat,maize and potato consumed water from evaporation and transpiration (ET) with the increase of 29.86%, 10.17% and 2.7% respectively under the P2 treatment ;and compared with the Pi, with the increase of 6.88%,4.92% and 0.30% respectively .3.irrigation and phosphorus application have also significant influence on water use efficiency (WUE) based on ET, Phosphorus application increased crop WUE in this experiment ,which differed entirely from the effection of irrigation .By calculating the average WUE of three kinds of crops . the order of WUE was found to be: W2P2>W1P2>W1P1> W1P0> W2P0>W2P1 > W3P1> W3P2 > W3P0.So, the highest WUE with the highest grain yield correspondingly was under the W2P2 .The effect of phosphorus and irrigation on water consumption and WUE could be estimated from the linear eqation below:Note : x1-phosphorus, x2-irrigation , Y-yield,ET-water consumption,W-wheat,P-potato,C-com ,M-oloculture,I-Intercropping.*Correlation is significant at the 0.05 level (2-tailed).** Correlation is significant at the 0.01 level (2-tailed).4. Crops have the highest economic yield under the condition of appropriate irrigation and adequate phosphorus application in this experiment. It was showed in the field-formulating experiment that wheat seed yield increase by 239.56% in phosphorus supply. Yield was significantly different (a=0.05,LSD) among the treatments ,and the treatment with phosphorus and light water stress has the highest yield . In field experiment ,the economic...
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