Drought and Waterlogging Characteristics during the Grow th Period of Summer Maize in Luxi Plain Areas

Peiliang SUN，Xu LIU，Caibo FENG，Yaping LI

Liaocheng Meteorological Bureau，Liaocheng 252060，China

Liaocheng，also known as the Water City，is a prefecture-level city in western Shandong province，People's Republic of China.It borders the provincial capital of Jinan to the southeast，Dezhou to the northeast，Tai'an to the south，and the provinces of Hebei and Henan to the west.The prefecture-level city of Liaocheng administers eight county-level divisions，including one district，one county-level city，and six counties.Liaocheng is located in the west of Shandong with Mount Taias its close neighbor.The area of arable land is577.5 hm2，and the main planting pattern is winter wheatsummer maize cropping.In recent years，with the rise of the market demand for corn，the planting area of summer maize has showed an increasing trend，and the perennial planting area of summer maize has reached 367.5 hm2，with the yield per unit of about7 000 kg／hm2.Liaocheng City features a semi－arid continental climate，with the annual precipitation of only 566.7 mm，and the precipitation during June to August accounting for 62.9%of total annual precipitation［1－2］.Under high yield conditions，the soil moisture remains at about80%of field moisture capacity during the growth period of summer maize，and the amount of water needed during the growth period is417.30－507.45 mm［3］.Conspicuously，the precipitation does not meet the high yield requirements.The precipitation is highly concentrated，and the formation of waterlogging disaster is inevitable，so drought or waterlogging has become one of the main meteorological disasters limiting the high yield and quality of summer maize in Liaocheng City.According to statistics，the average annual summer maize drought-hit area accounts for 50%of the total area，and the waterlogging disaster area accounts for 18%of the total area［4］.

Therefore，based on the observed data of Liaocheng agro-meteorological observatory，we analyze the drought and waterlogging characteristics during the growth period of summer maize over 50 years in Liaocheng City，in order to provide a reference for scientific disaster prevention and mitigation，reducing the impact of drought and waterlogging on summer maize production，and ensure high yield and quality.

1　Materials and methods

1.1Data sources and processing （i）The growth period data of summer maize are from the agricultural meteorological observation reports of Shandong Liaocheng national agricultural meteorological observation station.（ii）The meteorological data are from the atmospheric observation report of Liaocheng national standard meteorological observation field.（iii）In accordance with the provisions of Agro-meteorological Observing Practices of China Meteorological Administration，the growth period of maize is divided into ten stages：sowing，seedling emergence，three-leaf stage，seven-leaf stage，elongation，tasseling，flowering，silking，milky ripe stage and maturity.According to the characteristics of needs for water during the different growth stages of summer maize，the growth and development period of summer maize is divided into four main phases：seedling stage（sowing-seedling emergence），elongation stage（three-leaf stage-elongation），flowering stage（tasseling－flowering），maturity stage（silking-maturity）.The statistical period of precipitation takes the average annual growth period of summer maize in Liaocheng City as the statistical date limit（Table 1）.

1.2Drought and waterlogging index calculation method

The ratio of the natural rainfall within the growth period of summer maize to the physiological water demand threshold during the growth and development period，is used to calculate the drought and waterlogging index，which can better reflect the impact of drought and waterlogging on the growth and development of summer maize.The specific formula is as follows［4－12］：

where K is the drought and waterlogging index；S is the available water during the growth period（in this article，it refers to the natural precipitation within the growth period of summer maize（mm）；D is the physiological water demand of summer maize（Table 2）.The ratio of the average water demand within the growth period of summer maize to the minimum water demand and the ratio of the average water demand within the growth period of summer maize to the maximum water demand，is used as the basis for the grade classification of drought and waterlogging grade index.

According to the value of K，the drought and waterlogging index is divided into five grades：severe drought0.7≤K；drought0.7＜K≤0.9；normal0.9＜K≤1.1；waterlogging 1.1＜K≤1.3；severe waterlogging 1.3＜K.

1.3Calculation method of climate trend rate Climate trend rate uses the simple regression equation method.Assuming the data sequence is Y，and the time sequence is x.x is the year sequence number（1，2，......n），then：

b×10 is the climate trend rate，namely the climate change trend every 10 a.The positive value means that Y increases over the time and the negative value means that Y decreasesover the time.

Table 1 The average grow th period of summer maize during the period 1961－2011

1.4Regional distribution technology GIS technology is used to carry out the analysis of regional distribution characteristics.

2　Results and analysis

2.1Drought and waterlogging analysis （i）According to the calculated drought and waterlogging index during the growth period of summer maize in Liaocheng City from 1961 to 2011，the frequency of drought and waterlogging disasters is as high as81.5%.In the natural rainfall conditions，the probability of occurrence of drought and waterlogging during the growth period of summer maize in Liaocheng City is eight in ten years，with frequent drought and waterlogging.The drought is significantly more than waterlogging，and the drought frequency is61.8%.The frequency of occurrence of severe drought is 34.3%.The frequency of occurrence of waterlogging is 19.8%，and the frequency of severe waterlogging is7.3% （Fig.1）.

Table2 The physiological water demand during various grow th stages of summer maize

（ii）The regional characteristics of drought and waterlogging are very obvious.The frequency of drought in the western region is significantly higher than that in the eastern region，and it is the highest in the southwestern region.The waterlogging is the other way around，and the frequency of waterlogging in the eastern region is significantly higher than that in the western region，the highest in the southeast（Fig.2）.

（iii）Along with the global warming climate change，during the growth period of summer maize，the entire Liaocheng region shows the climate trends of conversion to drought（The climatic trend rate of drought and waterlogging index in Liaocheng，Linqing，Gaotang，Chiping，Dong'e，Yanggu，Shenxian and Guanxian is－0.012，－0.028，－0.019，－0.029，－0.038，－0.029，－0.033，－0.012，respectively，with the regional average of－0.025），which poses grimmer situation for the Liaocheng region whose natural precipitation can not meet the requirements of high yield and quality cultivation of summer maize.Since the 1980s，the frequency of droughtand waterlogging during the growth period of summer maize has been significantly increased，and the disasters of droughts and waterlogging have had an increasingly serious impact on summer maize production.Especially in the tasseling and silking period of summer maize，the drought will seriously affect the yield and quality.

In the late growth period of summer maize in 2002，the scarce rainfall resulted in serious reduction of output of summer maize，and in Liaocheng City，2.1×104hm2of summer maize was affected by the disaster and 7.7×103hm2of summer maize underwent crop failure.During the filling period of summer maize in 2011，the rainy weather resulted in the reduction of output of summer maize more than 10%，and delayed the maturity period of summer maize compared to normal years，affecting the timely sowing of winter wheat and making some winter wheat fail to produce tillers before winter.

2.2Analysis of drought and waterlogging situation at different stages of grow th Through the analysis of drought and waterlogging index at various developmental stages，it can be found that the frequency of occurrence of drought and waterlogging during the seedling period is up to100%，and the frequency of occurrence of drought accounts for 80.4%，that is，it is very prone to serious drought phenomenon，seriously affecting the normal growth and development of summer maize during the seedling period.

The frequency of occurrence of drought and waterlogging during the elongation period is 82.4%，and the frequency of occurrence of waterlogging accounts for70.6%，that is，the water is too much，hampering the root growth，and the drought-resistant power of maize in the late period is weak.

Fig.1 The frequency of occurrence of drought and waterlogging in Liaocheng City（%）

Fig.2 Regional distribution of frequency of occurrence of drought and waterlogging

The frequency of occurrence of drought and waterlogging during the flowering period is 74.5%，and the frequency difference of droughts and waterlogging is the smallest in this period.

The frequency of occurrence of drought and waterlogging during the maturity period is90.2%，and the frequency difference of drought accounts for 86.3%.The natural rainfall is insufficient，affecting maize's filling rate and grain formation，and also affecting the yield and quality（Table 3）.

Table 3 The frequency of occurrence of drought and waterlogging at different stages of grow th（%）

At various stages of the growth period of summer maize，there is the climate trend of transforming to drought（The climate trend rate of drought and waterlogging index at the stages of seedling，elongation， flowering and maturity is －0.001， －0.088，－0.083，－0.007，respectively），which will further destroy the moisture supply and demand balance during the growth period of summer maize，and affect the high yield and quality cultivation.

At various growth stages，the regional characteristics of drought and waterlogging are more obvious.At the seedling stage，the drought is very serious in the central regions and most serious in the south-central regions（Fig.3-a）；at the flowering stage，the regional distribution is relatively even；at the elongation stage，the waterlogging is serious in the southern regions（Fig.3-b）；at the maturity stage，the drought is most obvious in the central areas（Fig.3-c）.

3　Conclusions and recommendations

Fig.3 The drought and waterlogging frequency of maize during various grow th stages and regional distribution

3.1Conclusions Liaocheng City is located in the irrigation area of lower reaches of the Yellow River，and with the accelerated process of the development in the Yellow River Delta，the industrial and domestic water demand is increasing year by year，so it is extremely difficult to increase the water diversion to solve the problem of water shortage for the growth of summer maize.Based on this，the fundamental way to solve water shortage problems for summer maize is to develop high-yielding and water-saving cultivation techniques of summer maize，research the laws of occurrence of drought and waterlogging，store water when there is waterlogging，save water when there is drought，make full use of groundwater，scientifically develop the air resources，and regulate the water supply and demand balance at different growth stages of summer maize［13］.

3.2Recommendations We put forth the following recommendations：

（i）Selecting drought-resistant varieties，and improving the water resource use efficiency.

（ii）Promoting the water and fertilizer coupling，sprinkler irrigation，drip irrigation，micro-irrigation and other water-saving irrigation technologies，and improving the water use efficiency.

（iii）Promoting the ditch，ridge and laminating cultivation technology，reducing the field evapotranspiration，keeping warming and conserving moisture，and saving water resources.

（iv）Strengthening the construction of water conservancy facilities，so that it can be irrigated during drought and drained during waterlogging.

（v）During dry season，timely organizing artificial rainfall operation，and increasing precipitation in arid areas to ease drought.

（vi）Rationally exploiting the groundwater，and improving the underground water use efficiency.Liaocheng，as the Yellow River alluvial plain，has abundant groundwater.The exploitation and utilization of groundwater should gradually shift from the role increasing water to the function of adjusting the seasonal imbalance between supply and demand of water，to improve the efficiency of utilization of groundwater resources.

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