## 1 Introduction  
Reduction of yield in corn at harvest has been estimated from 5% to 20% per year globally [1]. Stalk lodging resistance is one of the major factors that influence on both yield and quality of corn. Accurate information about the properties of corn stalk lodging resistance has not been obtained due to field experimental limitations [2]. As is already known, the strength of the corn's stalk is associated with internode length and thickness [3]. Consequently, the stalk lodging rate is influenced by the same factors (i.e., internode length and thickness). Both stalk and root lodging occur under strong winds before harvest. Fracture or recurrent arching of the lower stalk internodes are known to be two causes of stalk lodging. Root lodging refers to stalks leaning from the crown, and involves a certain disturbance of the root system. In the past, selection of corn varieties possessing high lodging resistance depended on counting lodged plants by harvest [4]. This method, however, is disadvantageous, as a high coefficient of variation is frequently produced by various uncontrolled environmental factors such as wind and rain storms [5; 6; 7]. For instance, a harsh wind storm may lead to flattening of a whole corn field irrespective of the lodging resistance of stalks in the field, and therefore makes it hard to discriminate stronger varieties from weaker ones [8; 9; 10]. Wind-induced corn stalk lodging often occurs during the mid-growing season, when soil has been saturated by heavy rainfall and the rainfall is accompanied or followed by a high wind speed [11; 12; 13].  
At present, wind tunnel experiment in a laboratory is used in approximating the stalk lodging characteristics [14; 15]. In this method (i.e., wind tunnel experiment), a direct relationship is deduced between the stalk lodging resistance and the wind speed [16; 17]. Though the wind tunnel experiments are useful in intuitively determining the stalk lodging resistance in corn, it has a drawback in that it is unsuitable for on-site quantitative studies [18]. Other laboratory measurements of stalk lodging resistance include hydraulic machinery, such as stalk crushing strength (SCS) and rind penetrometer resistance (RPR), which provides mechanical characteristics of corn stalks [19; 20; 21; 22]. For rapid corn stalk lodging resistance measurements, a stalk hardness meter was developed, and it showed that the stalk strength decreased with planting density increase for the same corn varieties [23; 24]. Mechanical measurements of stalk strengths are time-consuming methods, and at the same time destructive (crush the stalk or physically break) [25; 26]. Moreover, rind penetration resistance, a method that has been used for many years, cannot fully show how corn stalk lodging is related to the natural wind due to the influence of probe shapes [27; 28].  
Rapid advances in lodging resistance measurement can be attained by establishing new testing procedures that approximate stalk lodging resistance without any influence from environmental factors [29]. A portable instrument for real-time measurement of corn stalk bending strength has been demonstrated successfully [30]. However, in order to solve problems caused by any single factor that was chosen to classify the stalk lodging resistance, the present study proposes a novel method for estimating corn stalk lodging properties by employing the singular value decomposition (SVD) algorithm and how it can be used in classifying corn varieties. This classification method does not only consider corn stalk lodging in relation to stalk resistance, but also provides a potential selective plant breeding tool for agricultural scientists.