Effects Of Organic Fertilizer Application On C,N Stoichiometric And Photosynthesis Of Spring Wheat Under Whole Field Soil-plastic Mulching And Bunch Seeding

Soil-plastic mulched and bunching seeding is one of the main cultivation methods for wheat in semiarid areas.This method usually adopts a single basal application of chemical fertilizer,which can lead to shortage of fertilizer later in the growing season,and it can affect the development of water production potential in wheat.Optimization of nutrient management to improve the efficiency of nutrient uptake and to realize efficient water and fertilizer use are therefore urgent problems to be solved for high yield and high efficiency production of wheat in semiarid areas.Currently,studies on yield increment in soil-plastic mulching technology are mainly focused on the relationship between soil thermal-moisture processes and yield composition.However,there is a lack of research into the relationship between soil water,carbon?C?and nitrogen?N?stoichiometrics,and photosynthesis,which is necessary in order to understand the mechanisms of wheat yield increments in response to plastic-soil mulching technology.This paper investigated the relationship from the perspective of chemometrics.Field experiments were conducted in the semiarid area of middle Gansu province,and involved three treatments:1)whole field soil plastic mulching and organic fertilization?PMO?,2)whole field soil plastic mulching?PMS?,3),and non-mulched and bunch seeded?CK?.The aims were to study changes in soil moisture,soil C and N stoichiometrics,and physiological characteristics of spring wheat;to analyze the effect of the relationships between these parameters on yield and water use efficiency,and to provide theoretical guidance for efficient fertilizer management of spring wheat.The main results are as follows:1.At the 0–300 cm profile,PMO enhanced soil water storage by 1.30–13.55%and 6.95–15.39%in whole wheat growth stages respectively,compared to PMS and CK.At the 0–300 cm profile,PMS soil water storage was lower than CK at the filling stage to the maturity stage,and it was reduced by 1.47–3.16%in the maturity stage compared to CK.Therefore,PMO can reduce water stress intensity and promote the increase and stable yield of spring wheat.2.PMO resulted in greater soil water storage in the middle and lower soil layers?100–300 cm?in the late growth period of spring wheat?from filling stage to maturity stage?than PMS and CK,whereas,PMS was lower than CK.The results showed that PMO could optimize the middle and lower soil water layers and reduce the risk of soil dry layer formation.Moreover,for soil fallow efficiency,it was increased by 16.67%and63.49%under PMO,compared to PMS and CK.PMO enhanced soil water storage by5.70%and 10.59%in the 0–300 cm profile in pre-sowing stages of wheat,compared to PMS and CK.Consequently,PMO could better store precipitation during the fallow period and spring wheat growth period,and reduce the negative impact of plastic film mulching in successive years on soil water balance in semiarid land.3.Through a field positioning test for two consecutive years,PMO averagely enhanced soil organic matter?SOM?content in the 0–30 cm profile by 50.04%and44.23%in pre-sowing stages of wheat in the second year,respectively,compared to PMS and CK.The average SOM content in the 0–50 cm soil layer of PMS was slightly lower than that of CK.In the whole wheat growth stages,PMO enhanced,on average,soil available nitrogen?SAN?content in the 0–50 cm soil profile by131.96%and64.39%,and soil organic carbon?SOC?content in the 0–30 cm soil profile by 50.04%and 44.23%,respectively,compared to PMS and CK.SOC content in the 0–30 cm soil profile was lower in PMS than CK.Moreover,PMO enhanced SAN accumulation in the 30–50 cm profile,respectively.Therefore,plastic film mulching may reduce the content SOM,SOC and SAN in the topsoil,but organic fertilizer application under plastic film mulching could significantly increase the content of SOM,which was beneficial to improve soil moisture and nutrient storage capacity,but promoted a surplus of SAN accumulation in the topsoil.4.From flag leaf stage to flowering stage,PMO significantly increased SAN content by 67.80%and 201.62%in the 0–30 cm profile,compared to PMS and CK.The decrease of SAN content in the 0–30 cm profile in the PMS treatment from heading to flowering stage was lower than CK.These findings indicated that PMO provided sufficient nitrogen for the growth of spring wheat compared to PMS and CK,and PMS might cause more restriction of soil nitrogen in the middle and later stages of wheat growth.Moreover,from the flagging to maturing stage,PMO averagely decreased SOC/SAN by 22.25%in the 0–30 cm profile,and by 60.22%in the 0–10 cm profile compared to PMS and CK,respectively.From heading stage to the filling stage,PMO averagely decreased the C/N of flag leaf by 5.72%and 23.73%,respectively,compared to PMS and CK.The results indicated that PMO can reduce the C/N ratio in topsoil during the growth and development of spring wheat which can alleviate the competition between spring wheat and soil for available nitrogen,thus relieving nitrogen limitation;and improving nitrogen supply,and to promote the distribution of N to flag leaves.5.During the whole growth period,PMO increased the SPAD value of leaves and the biomass per plant,and decreased the canopy temperature respectively,compared to PMS and CK.Compared with CK,the net photosynthetic rate,stomatal conductance,intercellular CO₂ concentration and transpiration rate of leaves from jointing stage to filling stage of PMO increased further than that of PMS,and the water use efficiency of leaves decreased.Compared to CK,PMO and PMS could significantly increase spike number per hectare,grain number per spike,and 1000-grain weight of spring wheat,but the increase of PMO was greater,and PMO grain yield was 9.11%and 53.74%higher than PMS and CK respectively;water use efficiency was 26.50%and 59.22%higher than PMS and CK,respectively.The results showed that PMO could improve chlorophyll content and reduce canopy temperature,and improve photosynthetic efficiency by alleviating water stress intensity and nitrogen limitation during the growth of spring wheat in semiarid land.This resulted in the accumulation of dry matter and grain solids,and optimized yield components,resulting in a significant increment of yield and water use efficiency.