| The agro-pastoral ecotone of North China is an intersection and transition zone of traditional agriculture and animal husbandry.Precipitation is the key yield-determining factor for rainfed agricultural production such as the agro-pastoral ecotone in North China with low amount and high variation of precipitation.Potato is the fourth largest food crop over the world and is also a staple crop in the agro-pastoral ecotone in North China.Both total amount of precipitation during potato growing season and the distribution of precipitation during different growth stages have important impacts on potato yield.Understanding the relationship between crop yield formation and precipitation and increase the match between precipitation and key water requirement period is important for increasing potato yield and ensuring local food security in the agro-pastoral ecotone.Adjusting planting date along with supplemental irrigation is widely used to narrow potato yield gap and increase water use effeciency in the agro-pastoral ecotone(APE).Serial planting experiment could make crop grow in different meteorological conditions within limited years and therefore is an efffecive method in determining optimal planting date and yield-controlling factors.Supplemental irrigation from rainfall harvesting could increase yield and water use efficiency of potato.Optimal planting date and time of supplemental irrigation depend on local rainfall year type and soil condition.Crop growth model could help analyze the optimal planting date and supplemental irrigation time and their interaction in the different regions and unde different climate year types.Supplmental irrigation could increase potato yield in the agro-pastoral ecotone,however,a large amount of irrigation is adverse to the sustainable development of agriculture in the region.Therefore,evaluating the impact of long-term cropping system under different agronomic managements on the change in soil moisture and groundwater is of significance to make sustainable development strategies for agriculture in arid and semi-arid regions.In this study,the yield-determining factor,optimal plating date of potato under different climate year types and different regions,and the impacts of different planting dates and irrigation schedules on potato yield,soil moisture and groundwater were ananlyzed based on the serial planting experiments and APSIM-Potato model.The study results showed that:(1)Potato yield had the highest correlation with the ratio of precipitation to potential evapotranspiration during the tuberization stage(PT/ETpT)(R2=0.51,P<0.01),followed by the effective precipitation during the post-tuber bulking period(EPpoTB)(R2=0.43,P<0.01)and during the entire growth period(EPgp)(R2=0.28,P<0.05).The potato yield was positively related to total solar radiation during the growth period(Sgp)(R2=0.37,P<0.01),especially during the pre-tuber bulking period(SprTB)(R2=0.44,P<0.01),while growth-period maximum temperature(Tmaxgp)had a negative effect on potato yield(R2=0.27,P<0.05).The multiple linear regression equation of potato yield and meteorological factors during the potato growth period showed that the variation in PT/ETpT,EPpoTB and SprTB could explain 71%of the variation in potato yield.The optimal planting dates,based on the 80th percentile of the highest yield related to PT/ETpT,EPpoTB and SprTB within the potential planting window from 1961 to 2010,were found to be May 27-June 12 for a wet year,May 3-May 26 for a normal year,and April 4-May 2 for a dry year,if sufficient soil moisture could ensure emergence of potato.(2)APSIM model performed well in simulating phenology,LAI,soil water dynamics,biomass of potato,and also captured the trend in potato yields under different planting dates.Based on the long-term simulations from 1981 to 2010,the optimal planting dates were May 10(local normal planting date),May 20 and May 30 in the eastern,middle and western APE,respectively.The optimal planting date produced higher potato yield and PWP by 12.5%and 7.0%in the middle APE,and 23.3%and 18.3%in the western APE,respectively,compared with the local normal planting date under rainfed condition.The supplemental irrigation(8-55 mm)from rainwater harvesting increased potato yield by 3.5-35.2%,6.9-41.8%,and 9.0-50.8%respectively,in the eastern,middle and western APE under normal planting date.The corresponding PWP could be enhanced by 1.2-22.7%,6.7-30.8%and 4.5-33.7%,respectively,in the three areas of APE.Combining the optimal supplemental irrigation times and above-mentioned maximal supplemental irrigation amount with the optimal planting dates increased potato yield and PWP by 36.8%and 23.4%,69.2%and 49.2%,64.3%and 48.8%,for the three areas of APE,compared with the simulation results under the local normal planting dates and rainfed condition.(3)Irrigated potential,rainfed potential fresh yields and their gap of potato ranged from 29000-39500,12000-24100 kg·ha-1 and 11400-24700 kg·ha-1,respectively in the agro-pastoral ecotone(APE)of North China.The rainfed potential yield only reached 35-67%of the irrigated potential yield.The yield gap was higher in the western APE due to lower pre-planting precipitation and match degree between the distribution of growing season precipitation and water requirement of potato than that in the middle and eastern APE.Potato yield could be enhanced by 41-86.8%in comparison with rainfed potential yield with the irrigation amounts of 60-240 mm and the yield gap between the irrigated potential yield and rainfed potential yield could be narrowed by 5-70%.However,applying irrigation amount of 60-240 mm would decrease the groundwater table by 4.2-44.8 m across the APE from 1981 to 2010.Continuous rainfed cropping system of potato(CP)could enhance the groundwater table by 0-3 m with supplement of precipitation but decreased soil available water at 1 m depth from 1981 to 2010.Cropping system with alternating planting and fallowing(AP)and long-term fallowing system(LFP)could increase soil available water at 1 m depth by 2-79 mm and 100-143 mm respectively,and groundwater table by 0-4.3 m and 6-16 m respectively compared with continuous cropping system from 1981 to 2010 in the APE.The study suggested that continuous rainfed cropping system of potato would decrease the soil moisture significantly which increase the risk of soil desertification in the APE.Alternating planting and fallowing could be a feasible way in maintaining soil available water and groundwater if government subsidy could guarantee the inputs of local farmers in the APE in North China. |
PDF Full Text Request