| Nitrogen and phosphorus are the two most important nutrient elements in the growth of rice,their circulation and migration not only affect the growth and production of rice,but also affect the safety of agricultural environment and human health.The lack of nitrogen and phosphorus will cause the slow development of rice and the decrease of yield,and the excessive input of nitrogen and phosphorus will reduce the utilization efficiency of fertilizer,aggravate the loss of nitrogen and phosphorus and cause agricultural pollution.On the basis of the previous studies,this paper takes the rice-fish ecosystem(RF)as an example to design two patterns of rice fish chicken and rice loach,and the addition of Azolla filiculoides Lamk in the system.5 treatments are designed:rice,fish and chicken(A);rice-fish-chicken-duckweed(B);rice-loach(C);rice-loach-duckweed(D);and conventional rice(CK).An attempt was made to establish a rice-fish ecosystem that could reduce the input of agro chemical products,be green and safety to the environment;study the effect of the system on rice yield,and to analyze the cycle and migration of nitrogen and phosphorus in the system,and the difference between the treatment of duckweed and non-duckweed in the system.Compared with control treatment,the main results are as follows:(1)RF significantly increased the yield of rice,and the average yield increased by12.13%(6.93%?22.23%).Compared with CK,the average grain number,effective spikes and seed setting rates of RF increased by 17.50%(8.01%?24.97%),8.42%(7016%?10.19%),4.01%(0.06%?8.13%),respectively.In addition,the yield increase of B and D in RF was greater than A and C that without duckweed,and the average yield increased by 4.55%.The yield of the rice and loach model was larger than that of the rice-fish-chicken model,and the average yield increased by 31.54%.(2)the average content of total nitrogen,alkali-hydrolysable nitrogen,total phosphorus and available phosphorus in the soil increased by 9.40%(5.98%?33.33%),10.47%(-11.46%?40.92%),16.10%(1.69%?27.12%)and 47.52%(41.78%?60.27%),respectively,due to the existence of fish,chicken and loach in RF.(3)the inputs of nitrogen and phosphorus in RF and CK are roughly the same,mainly from irrigation,rainfall and fertilization,and the output of nitrogen and phosphorus is calculated by the absorption of rice and aquatic products.compared with CK,the total nitrogen input of RF decreased by 22.37%(20.60%?24.03%),while the total nitrogen output increased by 29.71%(26.00%?35.11%).The total phosphorus input of RF is not significantly different from that of CK,but the total phosphorus output is increased by20.40%(13.79%?24.40%)over CK.The total nitrogen and total phosphorus output of B and D in RF which containing duckweed were 5.69%and 4.50%higher than A and C that without it,respectively.(4)the nitrogen balance of the RF treatment was positive,the nitrogen balance of CK was negative,the average nitrogen balance of RF was 90.36 kg/hm~2 higher than that of CK;and the phosphorus balance in the RF and CK treatments were all negative,but the phosphorus equilibrium of RF was greater than that of CK,the average phosphorus equilibrium of RF was 12.94 kg/hm~2 higher than that of CK.It is proved that fish,chicken and loach in RF promoted the balance of nitrogen and phosphorus in paddy ecosystem.In addition,the balance of total nitrogen and total phosphorus of B and D in RF containing duckweed was greater than non-duckweed treatment of A and C,average increased by10.98%and 1.73%respectively. |
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