Effects of Straw Return and Feed Addition on the Environment and Nitrogen use E ciency in the Rice–Cray sh System


 Purpose Understanding the direction of nitrogen flow in the rice-crayfish system (RC) and optimizing the rate of nitrogen fertilizer application (ORN) are of great significance for sustainable development of RC. Methods To this end, a field experiment involving straw and feed treatment was conducted to delineate the flow of the nitrogen present in the straw (straw-N) and feed (feed-N). Second, under different feed and straw treatments, we carried out a mesocosm experiment with different rates of 15N-labeled nitrogen fertilizer application to explore the optimal rate under the effects of feed-N and straw-N supply.Results The results showed that at 75 kg N ha-1(75N), 14% and 1.86% of feed-N and 4.3% and 8.78% of straw-N is absorbed by crayfish and rice, respectively. The percentage of feed-N and straw-N lost to the environment was the lowest at 75N, i.e., 84.48% and 86.92%, respectively. Using straw return to the field and feeding as the basic management measures for RC, we observed that the rice yield was the highest under 75N, and the highest nitrogen utilization efficiency (NUE) was 25%, and the highest the percentage of soil storing nitrogen by the fertilizer-derived was 34% (lost to the environment, at least 41%).Conclusions ORN could help in the effective utilization of feed-N and straw-N via a compensation effect, promote the absorption and transport of nitrogen, and ultimately lead to an improvement in NUE in RC.

respectively. Using straw return to the field and feeding as the basic 25 management measures for RC, we observed that the rice yield was the 26 highest under 75N, and the highest nitrogen utilization efficiency (NUE) 27 was 25%, and the highest the percentage of soil storing nitrogen by the 28 fertilizer-derived was 34% (lost to the environment, at least 41%). 29 Conclusions ORN could help in the effective utilization of feed-N and   In order to explore the impact of straw return and feed addition on the  In the non-rice season, straw was returned to the field using a    Stable isotope values were reported in δ notation: Where R is 15 N/ 14 N, and the standard sample used for determining 15 N 266 concentration is N 2 from the air ( 15 N = 0.003676).

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The percentage of nitrogen from the fertilizer in the total rice biomass-N 268 or total soil nitrogen was calculated as follows:  We estimated the percentage of fertilizer-derived nitrogen that was 275 used by the rice as follows: where N rice is the total rice biomass-N and N fertilizer is total fertilizer-N 277 in the mesocosms experiment. 278 We estimated the percentage of fertilizer-derived nitrogen that was 279 stored by the soil as follows: where N dff is the percentage of fertilizer-derived nitrogen in the soil. The

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H value is 20, representing the thickness of the soil layer (cm). BD is soil 283 bulk density (g cm 3 ), and TN soil is the TN content of the soil (g kg -1 ).

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N fertilizer is 15 N-labeled urea nitrogen content (kg ha -1 ) and the 10 is for unit yield of crayfish in SN was significantly higher than that in NN (p<0.05).

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Although there was no significant difference in crayfish production 321 between SF and NF, the crayfish production with SF treatment was 9% 322 higher than that with NF treatment ( the environment was reduced to 84.48% (Fig. 2b).

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Under different rates of nitrogen application, 4.3% of straw nitrogen 345 was absorbed by crayfish (Fig. 2) was absorbed by the rice, respectively (Fig. 2a, b, c, d). With the increase 348 in nitrogen rates, the amount of straw nitrogen lost to the environment 349 increased (Fig. 2).   under different straw and feed treatments in RC fields is shown in Figure   380 3. The storage of fertilizer nitrogen in the soil (Rsoil(%)) was calculated 381 using formula 9 and the soil bulk density value ( in the nitrogen levels across micro areas with these application rates. treatments than in the NN and SN treatments (Fig. 4) (Fig. 3). Although under the NF condition, the Rloss(%) was not 436 significantly different between 75N and 150N, the Rloss(%) at 150N was 437 15% higher than that at 75N (Fig. 3). Under the SF condition, although 438 the dry matter accumulation in rice stems and leaves was the highest at an 439 application rate of 225N, the dry matter in the grains was the lowest 440 (Table 2). Further, the total nitrogen accumulation in the stems, leaves, 441 and grains was the lowest under SF treatment (Fig. 4). The excessive use     13.9 ± 7.6a 21.7 ± 5.7a 20.0 ± 9.9a 21.1 ± 12.0a water content(%) 0.7 ± 0.0a 0.7 ± 0.0a 0.8 ± 0.0a 0.7 ± 0.0a TN(g kg -1 ) 6.9 ± 0.4a 6.6 ± 0.4a 6.4 ± 0.7a 6.4 ± 0.9a Crayfish yield (t ha -1 ) 0.6 ± 0.02c 1.2 ± 0.03a 0.7 ± 0.01b 1.