Root Distribution And Water Consumption Of Wheat/Maize Intercropping System

Intercropping systems comprise intensive planting practices.They have attracted increasingly greater attention as a strategy to alleviate the negative impacts of arable land reduction,land degradation,and climate change on agricultural productivity.Water consumption and productivity of intercropping systems under rainfed and supplementary irrigation conditions in semi-arid and semi-humid areas need to be further studied The objective of this study was to clarify the mechanisms affecting productivity and water consumption advantages of intercropping systems under rainfed and supplementary irrigation conditions in semi-arid and semi-humid areas based on root characteristics(root growth and root distribution),water consumption characteristics(soil moisture,evapotranspiration,water migration,sap flow),and water consumption assessment in a wheat/maize intercropping system.The water consumption evaluation index of the intercropping system was optimized by considering the consistency of the water consumption period and ecological benefits.Doing so permitted the objective and accurate evaluation of the water consumption characteristics of the intercropping system,which is more suitable for strategies such as fallow as a new trend in agriculture.The main conclusions were as follows:(1)Exploring root system characteristics and water competition of the intercropping system.Under rainfed conditions,intercropping promoted wheat root growth and spatial distribution,significantly increased wheat total root length,and significantly increased the asymmetrical distribution of the wheat root system.These changes resulted in wheat having greater access to soil moisture.Distribution of intercropped maize roots were inhibited both horizontally and vertically.There was no significant recovery in maize roots after wheat harvest,and their water use range and capacity were severely limited.Under supplementary irrigation,the lateral distribution of intercropped wheat roots was not obvious.After wheat harvest,the recovery of maize roots was promoted,the total root length was significantly increased,and the root system was significantly increased mainly in the horizontal direction,thereby improving the water absorption capacity of maize.Wheat was more competitive for water than maize due to the greater plasticity of the wheat root system,and this difference was particularly evident under rainfed conditions.(2)Identification of reasons for the advantages and disadvantages to wheat and maize transpiration in the intercropping system.Intercropping increased wheat transpiration under both rainfed and irrigated conditions,while intercropping increased maize transpiration only under supplemental irrigation.Under rainfed conditions,both border rows and inner rows of intercropped wheat had higher sap flow compared with sole wheat,but the greater sap flow was mainly observed for border rows.Specifically,in the wet season,the daily sap flow for the border row and inner rows of intercropped wheat increased by 38-45% and 2-7%,respectively,compared with sole wheat.In the dry season,daily sap flow for the border row and inner rows of intercropped wheat increased by 56-140% and 17-20%,respectively,compared with sole wheat.Intercropped wheat had greater drought resistance than sole wheat.Under supplementary irrigation,the transpiration advantage of intercropped maize was mainly due to the significant increase in maize sap flow after wheat harvest.During the key growth period for maize,sap flow values at different locations ranked in the order of border row> inner row> sole maize.Before wheat harvest,under the same water treatment,there was no significant difference in soil evaporation between different planting patterns.After wheat harvest,soil evaporation in the intercropped wheat strips was significantly less than observed in sole wheat.Soil evaporation in the intercropped maize strips was significantly larger than observed for sole maize.(3)Clarification of water migration and evapotranspiration partitioning in the wheat/maize intercropping system.There was a large amount of water migration between the wheat strip and the maize strip in intercropping,and the migration direction changed with the growth period.Under both rainfed and irrigated conditions,water migrated from the maize strip to the wheat strip before wheat harvest,and water migrated from the wheat strip to the maize strip after wheat harvest.Compared with the rainfed treatment,irrigation reduced the water migration amount from the maize strip to the wheat strip before wheat harvest,but increased the water migration amount from the wheat strip to the maize stirp after wheat harvest.Wheat canopy interception accounted for 11–22% of the evaporation,and maize canopy interception accounted for 11–26%.Except for the irrigated treatment in 2015,there was no significant difference in wheat canopy interception between different planting patterns.Under rainfed conditions,intercropped maize canopy interception was significantly lower than that of sole maize.There was no significant difference in canopy interception between sole maize and intercropped maize under irrigated conditions.Significantly greater water consumption was observed for intercropped wheat and intercropped maize than for sole cropping during the growth period.The increase in water consumption of intercropped wheat was due to the increase in evaporation and transpiration,and there was no significant difference in the T/ET ratio between sole wheat and intercropped wheat.The increase in water consumption of intercropped maize was due to the increase in evaporation,and the E/ET ratio of intercropped maize increased significantly compared with sole maize.(4)Clarification of the yield advantage,land use advantage,and water consumption advantage of the intercropping system.Under both rainfed and supplementary irrigation conditions,the intercropping system exhibited yield and land use advantages over the sole crop system.The yield increase of intercropped wheat relative to sole wheat was greater under rainfed conditions than under irrigation.Intercropped maize yield was 6% less than sole maize yield under rainfed conditions,but with supplementary irrigation,intercropped maize yield was 7% greater than sole maize yield.Based on the ΔWU and ΔWUE indicators proposed by Morris et al.,this study accounted for water consumption during the non-growth period of the sole cropping system,and additionally accounted for the ecological benefits of intercropping.Based on the optimized evaluation index,the water use efficiency of the wheat/maize intercropping increased and the total water consumption decreased.The results of this study indicated that when constructing an intercropping system,full consideration must be given to root growth characteristics and the resultant competition for water.The wheat root system exhibited stronger plasticity and greater capacity for water absorption than the maize root system,which resulted in yield and sap flow advantages,and greater ability to resist drought.Intercropped maize had advantages for root growth,sap flow,and yield only under supplemental irrigation.Compared with sole cropping,the intercropping system had advantages for yield,land use,and water use,and these results are of great significance for rainfed areas.These results are extremely important for further building and optimizing intercropping systems,evaluating the regional suitability of intercropping systems,and improving water management of intercropping systems.Intercropping systems used as a fallow practice have advantages with respect to water conservation and increased yield,and have potential to increase ecological and economic benefits.