Department of Environmental Sciences, Government College University, Faisalabad, Faisalabad, Punjab, Pakistan.
Institute of Soil and Environmental Sciences, University of Agriculture Faisalabad, Faisalabad, Punjab, Pakistan.
PeerJ. 2024 Sep 5;12:e17984. doi: 10.7717/peerj.17984. eCollection 2024.
Sequestering carbon dioxide (CO) in agricultural soils promises climate change mitigation as well as sustainable ecosystem services. In order to stabilize crop residues as soil carbon (C), addition of mineral nutrients in excess to crop needs is suggested as an inevitable practice. However, the effect of two macronutrients ., nitrogen (N) & phosphorus (P), on C cycling has been found contradictory. Mineral N usually decreases whereas mineral P increases the soil organic C (SOC) mineralization and microbial biomass. How the addition of these macronutrients in inorganic form to an organic-matter poor soil affect C cycling remains to be investigated.
To reconcile this contradiction, we tested the effect of mineral N (120 kg N ha) and/or P (60 kg N ha) in presence or absence of maize litter (1 g C kg soil) on C cycling in an organic-matter poor soil (0.87% SOC) in a laboratory incubation. Soil respiration was measured periodically during the incubation whereas various soil variables were measured at the end of the incubation.
Contrary to literature, P addition stimulated soil C mineralization very briefly at start of incubation period and released similar total cumulative CO-C as in control soil. We attributed this to low organic C content of the soil as P addition could desorb very low amounts of labile C for microbial use. Adding N with litter built up the largest microbial biomass (144% higher) without inducing any further increase in CO-C release compared to litter only addition. However, adding P with litter did not induce any increase in microbial biomass. Co-application of inorganic N and P significantly increased C mineralization in presence (19% with respect to only litter amended) as well as absence (41% with respect to control soil) of litter. Overall, our study indicates that the combined application of inorganic N and P stabilizes added organic matter while depletes the already unamended soil.
将二氧化碳（CO）封存在农业土壤中有望实现减缓气候变化和可持续生态系统服务的双重目标。为了将作物残茬固定为土壤碳（C），建议添加超出作物需求的矿物质养分，这是一种不可避免的做法。然而，两种大量营养素——氮（N）和磷（P）对 C 循环的影响却存在矛盾。通常情况下，添加矿物质 N 会减少土壤有机碳（SOC）矿化和微生物生物量，而添加矿物质 P 则会增加这种情况。向有机质贫化土壤中添加这些大量营养素的无机形式如何影响 C 循环仍有待研究。
为了解决这一矛盾，我们测试了在有无玉米秸秆（1 g C kg 土壤）的情况下，添加矿物质 N（120 kg N ha）和/或 P（60 kg N ha）对贫有机质土壤（SOC 为 0.87%）中 C 循环的影响。在培养过程中定期测量土壤呼吸，而在培养结束时测量各种土壤变量。
与文献相反，P 添加在培养初期非常短暂地刺激了土壤 C 矿化，并释放出与对照土壤相似的总累积 CO-C。我们将其归因于土壤有机碳含量低，因为 P 添加只能解吸少量微生物可用的易位 C。添加 N 和秸秆增加了最大的微生物生物量（比仅添加秸秆增加 144%），而与仅添加秸秆相比，没有进一步增加 CO-C 的释放。然而，添加 P 和秸秆并没有增加微生物生物量。无机 N 和 P 的共同施用显著增加了有秸秆存在（与仅添加秸秆相比增加 19%）和不存在（与对照土壤相比增加 41%）的情况下的 C 矿化。总的来说，我们的研究表明，无机 N 和 P 的联合施用稳定了添加的有机物，同时耗尽了未经修饰的土壤。
