有机肥替代化肥对陇中旱区玉米生长及农田碳排放的影响

  【目的】  为降低陇中旱农区化肥氮用量且确保该区玉米持续绿色高产，开展了有机肥替代化肥对玉米生长、农田碳排放影响及机理的研究。  【方法】  试验采用单因素随机区组设计，在等氮 (N 200 kg/hm2) 条件下，设5个有机肥氮替代化肥氮比例处理:0 (T1)、50.0% (T2)、37.5% (T3)、25.0% (T4)、12.5% (T5)，同时设置一个不施肥处理 (T6)。在玉米拔节期、大喇叭口期、灌浆期、成熟期，取样测定玉米叶面积指数和干物质量，成熟期测产，并测定不同土层土壤pH、有机碳和全氮含量。在玉米播种后至收获，每隔15天测定一次CO₂通量。  【结果】  玉米叶面积指数、干物质积累量、生长率及籽粒产量表现为T1≈T5≈T3>T4>T2>T6。收获后，T3处理土壤pH与T1处理在0—5、5—10、10—30 cm土层差异均不显著。土壤有机质含量在0—5 cm土层中最高，T3较T1、T4、T5处理分别显著提高34.5%、9.9%、38.8%；5—10 cm土层内，T3处理的有机质含量与单施化肥T1处理差异不显著，T2、T3、T4处理间有机质含量差异不显著；10—30 cm土层T3较T1显著提高土壤有机质含量31.4%，较T5处理显著提高26.1%。全氮含量在5—10 cm土层中最高，T3较T1处理显著降低23.6%，各有机肥替代化肥比例处理间差异不显著。与T6处理相比，所有施肥处理均增加了玉米全生育期的总碳排放量，而在所有施肥处理中，T1、T3与T5碳排放总量较低且相互之间无显著差异。所有施肥处理较不施肥处理(T6)均提高了净生态系统生产力(NEP)和土壤碳平衡(SCB)，T3处理2019和2020年2年平均SCB高于其他所有处理，玉米农田均为大气CO₂的“汇”，T3表现出最强碳汇效应。相关性分析结果表明，土壤碳排放与土壤有机质含量(r=0.56*)、土壤温度(r=0.93**)呈显著或极显著正相关；与土壤pH呈极显著负相关(r= –0.77**)；叶面积指数(r=0.75**)、干物质(r=0.75**)、籽粒产量(r=0.93**)与土壤碳平衡呈极显著正相关；土壤理化指标中全氮 (r=0.72**)、温度(r=0.84**)与碳平衡间呈极显著正相关。  【结论】  在丰水年，陇中旱农区在施纯N 200 kg/hm2的水平下，37.5%左右有机肥替代化肥比例较单施化肥可使玉米稳产，改善土壤pH、提高土壤肥力，土壤CO₂排放总量较单施化肥处理没有显著增加，为陇中旱农区全膜双垄沟播玉米有机肥替代化肥的适宜比例。

Effects of substitution of chemical fertilizer by organic fertilizer on maize growth and field carbon emission in dry farming area of Longzhong,Gansu Province

  【Objectives】  Replacing a certain ratio of chemical fertilizers with organic fertilizer effectively reduces the total chemical fertilizer input. Here, we investigated the effects of replacing different ratios of chemical fertilizers with organic sources on maize growth and carbon emission in dry farming areas of central Gansu Province.  【Methods】  A field experiment was conducted in 2019 and 2020 in Lanchou City. Keeping an equal total N input of 200 kg/hm2, the five organic fertilizer N substitution rates were 0 (T1), 50.0% (T2), 37.5% (T3), 25.0% (T4), and 12.5% (T5), and there was a no fertilizer control (T6). Leaf area index and dry matter were measured at jointing stage, trumpeting, filling, and maturity, and yield was measured at maturity. Soil pH, soil organic carbon, and total nitrogen content were measured in different soil layers. CO₂ fluxes were monitored every 15 days after sowing until harvest.  【Results】  Throughout the maize reproductive period, leaf area index, growth rate, and grain yield were in the order T1≈T5≈T3 > T4 > T2 > T6. Soil pH was not different (P>0.05) in 0–5, 5–10, and 10–30 cm soil layers between T3 and T1 after harvest. The highest soil organic matter content was recorded at the 0–5 cm layer. The organic matter content of T3 in 0–5 cm soil (P<0.05) was 34.5%, 9.9%, and 38.8% higher than in T1, T4 and T5, respectively. The organic matter of T3 was not different (P>0.05) from T1 in 5?10 cm soil. In contrast, there was no difference (P>0.05) in the organic matter content among T2, T3, and T4. T3 (P<0.05) increased soil organic matter by 31.4% compared to T1 and 26.1% compared to T5 in 10–30 cm layer. The highest total nitrogen content was recorded in the 5–10 cm soil layer; total N in T3 significantly decreased by 23.6% compared to T1, and the differences among treatments of different proportions of substitution were not significant (P>0.05). Compared to T6, all fertilizer treatments increased total carbon emissions throughout the maize reproductive period. Notably, T1, T3, and T5 had lower total carbon emissions among all fertilizer treatments and were not (P>0.05) different. All fertilizer treatments increased net ecosystem productivity (NEP) and soil carbon balance (SCB) compared to T6, with the average SCB of 2019 and 2020 under T3 having a higher value than other treatments. The maize fields were all sinks for atmospheric CO₂, with T3 showing the highest carbon sink effect. Correlation analysis showed that soil carbon emission was positively correlated with soil organic matter content (r=0.56*) and soil temperature (r=0.93**, P<0.05), and negatively correlated with soil pH (r= –0.77**), SCB was significantly correlated with leaf area index (r=0.75**), dry matter (r=0.75**), seed yield (r=0.93**). The carbon balance was positively correlated with total N (r=0.72**) and temperature (r=0.84**).  【Conclusions】  Applying 200 kg/hm2 of pure N in the dry farming area of Longzhong during water abundant years shows that the proportional replacement of chemical ftilizers with organic fertilizer could help improve maize yield. Replacing 37.5% of urea with organic fertilizer maintains a stable yield compared to urea alone, improves carbon sink, soil fertility and pH, but the total soil CO₂ emission is not significantly different. Thus, the appropriate proportional replacement of chemical fertilizer with organic fertilizer in the dry farming area of Longzhong benefits the full-film double-ridge furrow-sown maize.