Effect of plough pan thickness on crop growth parameters, nitrogen uptake and greenhouse gas (CO2 and N2O) emissions in a wheat-maize double-crop rotation in the Northern China Plain: A one-year study

Plough pan can affect crop growth, nutrient uptake and the fates of substances in the environment. To determine the effects of plough pan thickness on crop and environment, a field survey and a field experiment were conducted on a typical calcareous fluvo-aquic soil in a winter wheat-summer maize rotation system in Northern China Plain from 2014 to 2016. Specifically, the thickness of plough pans was surveyed in 108 field plots in 2014, and then based on the survey results a field experiment was established to study the effects of different plough pan thicknesses (PP15: 15 cm of plough pan; PP10: 10 cm of plough pan; PP5: 5 cm of plough pan; PP0: 0 cm of plough pan) on crop growth, nitrogen (N) utilization and the environment. The survey showed that the thickness of topsoil averaged at 14.7 cm, and the plough pan was approximately 15 cm deep. The plough pan was found at 76% of the survey locations, and it was distributed commonly from 15 to 30 cm beneath the soil surface. Breaking the original plough pan partially or completely could promote the net photosynthesis rate, leaf water use efficiency, crop yield, and N use efficiency, decrease N2O emission, but increase CO2 emission. Among all treatments, breaking plough pans completely (PP0) and by 2/3 (PP5) resulted in best crop performance, whose photosynthetic parameters (especially net photosynthetic rate and leaf water use efficiency) were significantly higher than PP10 and PP15. For both wheat and maize, PP5 resulted in greater yield (7 130 kg ha−1 for wheat and 8 240 kg ha−1 for maize) than other treatments. Although it did not differ with PP0 significantly, PP5 had significantly higher N uptake (410 kg ha−1) and N use efficiency (40.1%) than PP10 and PP15. The magnitude of N2O emission peak decreased with an increasing degree of plough pan breakage. The cumulative N2O emission and intensity in PP5 was obviously lower than that in PP10 and PP15. Annual cumulative CO2 emission did not differ significantly among PP5, PP10 and PP15. Net ecosystem productivity (NEP) of the rotation system increased as the thickness of plough pan decreased, so PP5 had relative higher NEP (9 740 kg C ha−1) than PP10 and PP15. Thus, considering better crop growth, higher yield, optimized N utilization, lower N2O and CO2 emissions, as well as higher NEP and less mechanical costs, breaking the original plough pan partially is a good choice to ameliorating the plough pan restrictions in the Northern China Plain.