Effects of Soil Moisture in Spring on Growth of Winter Wheat in North China Plain

Hongyan Wang1, Qiangzi Li1, Xin Du1*, Yewei Lu1, 2, Jilei Liu1 1. Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences, Datun Road, Chaoyang District, Beijing

100101, China 2. China University of Mining & Technology, Xueyuan Road, Haidian District, Beijing 100083, China

First author e-mail: wanghy@radi.ac.cn, *Corresponding author e-mail: duxin@radi.ac.cn

Abstract—Crop growth can reflect the growth status of crops, soil fertility and plant nutrition. The winter wheat of North China Plain is facing a number of environmental problems that threaten the crops growth and yield, such as, water resource shortage. Therefore, this paper selected the North China Plain (NCP) as study area, analyzed the effects of soil moisture in spring on growth of winter wheat and to find the dominant factor affecting winter wheat growing. In this paper, the leaf area index (LAI) was selected as the growth indicator, and the correlation between LAI and soil moisture in spring was analyzed based on long time series half-month data (from 1982 to 2010). The results showed that the growth of winter wheat mainly showed positive-low-negative correlation with the soil moisture from early February to late April in the NCP. The growth of winter wheat and the soil moisture show a significant positive correlation in February, especially in the northern of the NCP. And in this period water was the dominant factor affecting winter wheat growing. But in the southern of the NCP (Anhui and Jiangsu province), water had little effect on winter wheat growth. In the NCP, the correlation between the LAI and soil moisture was low and the absolute value of correlation coefficient was mostly less than 0.3 in March. In April, the growth of winter wheat showed negative correlation with the soil moisture in most parts of NCP, in addition to the eastern part of Jiangsu province.

Keywords—Soil moisture; winter wheat; growth; time series; LAI; North China Plain.

I. INTRODUCTION Wheat is the most widely grown crop and an essential

component of the global food security mosaic, which provides one-fifth of the total caloric intake of the population worldwide [1]. China is the largest wheat producer and consumer in the world and wheat is the third leading crop produced nationally. In 2010, China occupied 17.6% (115 million tons) and 11.2% (24 million hectares) of the world’s total production and harvest area, respectively [2]. Food production in the North China Plain (NCP) contributes about 15% of the whole production of China [3] and winter wheat is one of the most widely cultivated crops in the NCP. This region is characterized as irrigated with an intensive wheat-maize double cropping system and high yield potential [4-5]. The NCP contributes 50% of the nation’s wheat grain [6].

In the past few decades, the agricultural ecosystem of the NCP is facing a number of problems that threaten the system

stability and sustainability, such as, climate warming, water resource shortage, radiation decline, cultivar improvement, and soil and crop management. Climate warming and water resource shortage have been suggested as causes of wheat yield reductions [7-9]. Current knowledge indicates that soil moisture (SM) has a great impact on the accumulation and distribution of dry matter in wheat plant, which contributes more than 70% of grain yield [10]. Crop growth can reflect the growth status of crops, soil fertility and plant nutrition. The winter wheat growth and yield are closely related. Therefore, this paper selected the North China Plain as study area, analyzed the effects of soil moisture in spring on growth of winter wheat and to find the dominant factor affecting winter wheat growing. Based on the results, a variety of management measures can be adopted to ensure the normal growth of crops and to early predict the winter wheat yield.

II. STUDY AREA The study area, North China Plain (NCP), refers to the

alluvial plain north of the Yellow River, east of the Taihang Mountain and south of the Yan Mountain, the geographical coordinates range from 31.9°N and 112.0°E to 39.8°N and 122.5°E (Fig. 1). It includes the entire Tianjin municipality, the southern part of Beijing municipality, most part of Hebei, Shandong and Henan provinces, and the northern part of Jiangsu and Anhui provinces. It comprises about 340 administrative counties with a total population of about 260 M. It is the center of China’s political, economic and cultural development. The total land area is 40.4 Mha, of which 72% is farmland, 14% built-up land, 8% forestland and grassland, and 6% water bodies or no-used land, based on recent land use data interpreted from remote-sensing imagery. Of the total farmland, about 82% had access to irrigation in 2007 according to the available data from local yearbooks. In 2009, NCP produced around 195 Mt of food grains, which is about 40% of the total output in China (estimated based on the statistical data). Winter wheat and summer maize are the most important crops, normally grown in a double crop rotation using irrigation. Due to over-exploitation of groundwater for irrigation, NCP suffers from serious groundwater depletion. Periodically water shortage in the NCP is an important constraint in achieving high crop yields.

The NCP belongs to warm temperate semi-arid monsoon climate zone of the eastern Eurasia, with cold and dry winter and hot and rainy summer [11]. The average annual temperature of the NCP is 12–13℃, increasing from north to south. The annual sunshine duration is 2400–3100 h and the frost-free period is more than 200 days. The multi-year (1956–2010) mean precipitation is 540–600 mm/year, while that of the coastal area is approximately 600–650 mm/year. The seasonal distribution of precipitation is uneven, with about 75% of its precipitation occurring throughout the summer flood season from July to August [12]. The inter-annual variation of the precipitation is large, with precipitation of less than 400 mm/year for most areas in a dry year and more than 800 mm/year for most areas in a wet year [13]. The multi-year mean evaporation from water surface is 1100–2000 mm/year [11].

Fig.1. General Location of study area

III. DATA AND METHODOLOGY

A. Data The leaf area index (LAI) 15-day data set made from 1982

to 2010 at 10�10km pixel resolution and can be obtained freely from the NASA Earth Exchange (NEX) web site [14]. In this study, we selected the LAI as the growth indicator, and the correlation between LAI and soil moisture in spring was analyzed based on long time series half-month data (from 1982 to 2010).The soil moisture data we used were developed within the Soil Moisture Climate Change Initiative project, and the spatial resolution is 0.25*0.25° (http://www.esa-soilmoisture-cci.org). The soil moisture data had the same spatial resolution

with the LAI after resampling; the spatial resolution was 10*10km.

B. Methodology A correlation analysis was performed with the LAI half-

month data and the soil moisture in spring (2- 4 months) for each pixel. The large absolute correlation coefficient was selected from the correlation coefficients between the LAI and the soil moisture for different periods. With this approach, the best-correlated soil moisture periods and the position of these periods in time are variable. The general spatial features of the correlation coefficients and their corresponding period are then analyzed. The correlation analysis for each pixel is based on Eq. (1):

1

2 2

1 1

( )(( ) )

( ) (( ) )

n

k i k k i ki

n n

k i k k i ki i

LAI LAI SM SMr

LAI LAI SM SM

=

= =

− −=

− × −

∑

∑ ∑

（ ）

（ 1）（ ）

Where (LAIk)i is the LAI of the k half-month in the year i; (SMk)i is the soil moisture of the k half-month in the year i; and K=1,2,3…, 6.

IV. RESULTS To test the linear association between soil moisture and

growth of winter wheat in the spring, Pearson correlation coefficients were calculated for the soil moisture and LAI for each pixel with the half-month data (2- 4 months) from 1982 to 2010. Figure 2 is the maps of the correlation coefficient between the half-month LAI data and soil moisture. It can be seen from figure 2 that the growth of winter wheat mainly showed positive-low-negative correlation with the soil moisture from early February to late April in the NCP. It can be also seen that the growth of winter wheat and the soil moisture show a significant positive correlation in February, especially in the northern of the NCP. In the NCP, the correlation between the LAI and soil moisture was low and the absolute value of correlation coefficient was mostly less than 0.3 in March. In April, the growth of winter wheat showed negative correlation with the soil moisture in most parts of NCP, in addition to the eastern part of Jiangsu province.

Soil moisture is the principal factor limiting the growth of winter wheat in early February in the NCP. The areas which the LAI of winter wheat is most sensitive to soil moisture are mainly distributed in Hebei, Tianjin, Shandong and Henan province. The southern portions of the study area (Anhui and Jiangsu province) have greater amounts of precipitation and higher soil moisture, and the growth of crop showed negative of low correlations with the soil moisture. A possible explanation for this finding is that the soil moisture in these areas is comparatively high and is relatively adequate for crop growth. The temperature or light maybe the principal factor limiting the growth of crop in these areas.

<-0.75 -0.75 — -0.5 -0.5 — -0.3 -0.3 — 0 = 00 — 0.3 0.3 — 0.5 0.5 — 0.75 > 0.75

Fig.2. Distribution of correlation coefficients between the half-month LAI and soil moister data in spring (2- 4 months) in the NCP

V. CONCLUSION The study used long time series half-month leaf area index

data (from 1982 to 2010) to analyze the correlation between the growth of winter wheat and soil moisture in spring in North China Plain, and analyzed the spatial distribution of the relationship. The following conclusions were drawn from these analyses: the growth of winter wheat mainly showed positive-low-negative correlation with the soil moisture from early February to late April in the NCP. The growth of winter wheat and the soil moisture show a significant positive correlation and the water was the dominant factor affecting winter wheat growing in February, especially in the northern of the NCP. But in the southern of the NCP (Anhui and Jiangsu province), water had little effect on winter wheat growth. The correlation between the LAI and soil moisture was low and the absolute value of correlation coefficient was mostly less than 0.3 in

March. In April, the growth of winter wheat showed negative correlation with the soil moisture in most parts of NCP, in addition to the eastern part of Jiangsu province.

ACKNOWLEDGMENT This study was supported by the Key Research Program of

the Chinese Academy of Sciences (Grant No. KZZD-EW-08-05), and the Director Foundation of the Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences.

REFERENCES

[1] M. Reynolds, D. Bonnett, S.C. Chapman, R.T. Furbank, Y. Manes, et al. Raising yield potential of wheat. I. Overview of a consortium approach and breeding strategies. J. Exp. Bot, vol. 62, pp. 439–452, 2011.

[2] FAOSTAT. FAO, http://faostat.fao.org/site/567/default.aspx#ancor (accessed 16.06.13), 2013.

[3] C.M. Liu. Exploring an ecological benefit of South-to-North water transfers for rehabilitating groundwater systems in the North China Plain. South-to-North Transfers and Water Science & Technology, vol. 1, pp. 439–452, 2011.

[4] Y. Zhou, Z.H. He, X.X. Sui, X.C. Xia, X.K. Zhang, et al. Genetic improvement of grain yield and associated traits in the northern China winter wheat region from 1960 to 2000. Crop Sciense., vol. 47, pp. 245–253, 2007.

[5] Y. Liu, E. Wang, X. Yang, J. Wang. Contributions of climatic and crop varietal changes to crop production in the North China Plain, since 1980. Global Change Biology, Vol.16, pp. 2287–2299, 2010.

[6] National Bureau of Statistics of China, China Statistical Yearbook 2012. China Statistics Press, Beijing, China, 2012.

[7] F.L. Tao, M. Yokozawa, J.Y. Liu, Z. Zhang. Climate-crop yield relationships at provincial scales in China and the impacts of recent climate trends. Clim. Res., vol. 38, pp. 83–94, 2008.

[8] L.Z. You, M.W. Rosegrant, S. Wood, D.S. Sun. Impact of growing season temperature on wheat productivity in China. Agric. For. Meteorol., vol. 149, pp. 1009–1014, 2009.

[9] S. Piao, P. Ciais, Y. Huang, Z.H. Shen, S.S. Peng, et al. The impacts of climate change on water resources and agriculture in China. Nature, vol. 467, pp. 43–51, 2010.

[10] A.N. Ziaei, A.R. Sepaskhah. Model for simulation of winter wheat yield under dryland and irrigated conditions. Agric Water Manag, vol. 58, pp. 1–17, 2003.

[11] L. Yang, Y. Zhang, C. Liu. Research about function decline and sustainable exploitation of groundwater resource in North China Plain. Geotechnical Investigation & Surveying, vol. 6, pp. 45–55, 2013.

[12] H. Qin, A. Sun, J. Liu, C. Zheng. System dynamics analysis of water supply and demand in the North China Plain. Water Policy, vol. 14 pp. 214–231, 2012.

[13] W. Wang. Designing the evaluation modules of groundwater recharge in North China Plain. Master’s Thesis, China University of Geosciences (Wuhan), Wuhan, China, 2005.

[14] Z.C. Zhu, J. Bi, Y.Z. Pan, S. Ganguly, A. Anav, et al. Global Data Sets of Vegetation Leaf Area Index (LAI)3g and Fraction of Photosynthetically Active Radiation (FPAR)3g Derived from Global Inventory Modeling and Mapping Studies (GIMMS) Normalized Difference Vegetation Index (NDVI3g) for the Period 1981 to 2011. Remote Sensing, VOL. 5, PP. 927-948, 2013.