Original papersNondestructive measurement of husk-covered corn kernel layer dynamic moisture content in the field
Introduction
Rapid dehydration of corn kernels is an important factor in corn breeding and cultivation (Zhou et al., 2018), particularly for high plant densities and when mechanized harvesting is used. In mechanized harvesting of corn, if the kernel moisture content is too high, it generally results in mechanical damage; however, if the kernel moisture content is too low, it can cause harvesting losses. Nondestructive measurement of corn kernel moisture content and monitoring of the kernel dehydration process during the grain filling stage in the field to predict the kernel maturity time accurately are thus essential processes to maximize the corn yield (Herrmann et al., 2005, Martinez-Feria et al., 2019). The kernel moisture content at maturity affects the moisture content of the harvested kernels. In fact, the dehydration of corn kernels in the field includes two phases: i) maturation dehydration, and ii) post-maturity dehydration. Before the kernels reach physiological maturity, i.e., the maturation dehydration stage, large amounts of relocated assimilates are displaced into the kernels (Maiorano et al., 2014). The kernel dehydration rate in this phase is regulated by the growth and development processes. The husk moisture has a positive effect on kernel dehydration, and lower husk moisture content results in lower moisture in the harvested kernels (Kang and Zuber, 1989). At the post-maturity dehydration phase, moisture exchange between the kernels and the atmosphere is the only dissipation route available for kernel moisture loss and the kernel dehydration rate is not only determined by the air temperature and the relative humidity (Maiorano et al., 2014) but also is affected by the number, thickness and weight of the husks (Zhou et al., 2016).
The conventional method used to perform grain moisture measurements is the oven drying method. However, this method is time-consuming and involves some tedious procedures that cannot be adapted for nondestructive in situ measurement of the dynamic moisture content of husk-covered corn kernels in the field. Benefiting from the continuing development of microwave and radio frequency technologies, rapid nondestructive methods for measurement of grain moisture based on the dielectric properties of agricultural materials have been widely applied. Several studies measuring in situ corn kernel moisture content have been performed using pin-type or ring-type grain moisture analyzers (Fan et al., 2020, Filipenco et al., 2013, Hurburgh, 1985, Kang and Zuber, 1989, Kang et al., 1978, Reid et al., 2014, Reid et al., 2010, Spry, 1990, Spry, 1992, Zhang et al., 2016). After the kernels reach physiological maturity, the physiological role of the corn husks has been completed and the husks can then be removed to accelerate the kernel dehydration process. At this stage, the kernel moisture content can be measured using the pin-type or ring-type devices (Fan et al., 2020, Zhang et al., 2016). However, before the kernels reach physiological maturity, the husks protect the kernels and also serve as important nutrient assimilation and storage organs for the developing kernels (Araus et al., 2012, Mesterházy et al., 2012, Ning et al., 2012, Pengelly et al., 2011, Yan et al., 2011). Therefore, before maturity, nondestructive measurement of the moisture content of husk-covered corn kernels is a prerequisite. Although we previously developed a ring-type sensor connected to a network analyzer for post-maturity kernel moisture detection in corn without husks, it is not currently possible to determine in situ the moisture content of husk-covered kernels directly and noninvasively (Zhang et al., 2016). Other researchers have used pin-type sensors to impale husk-covered corn kernels to measure their moisture contents (Filipenco et al., 2013, Reid et al., 2014, Reid et al., 2010). However, these pin-type devices damage the developing kernels, particularly in the early stages of corn ear growth, which can cause disease and infection (Kebebe et al., 2015, Reid et al., 2014). In addition, the husks and the corn cobs affect the repeatability of kernel moisture content measurements when using these pin-type devices. Challenges thus remain in nondestructive measurement of the dynamic moisture content of husk-covered corn kernels in the field at present.
To measure the dynamic moisture content of husk-covered corn kernels noninvasively in the field during the grain filling stage, we propose a new measurement method based on vector reflection coefficients and a handheld device, and use quadratic function models for fitting of the corn moisture content. First, after the one-port calibration procedure of the handheld moisture detection device is performed, the vector reflection coefficients of the husk-covered corn ears, which are coupled via the double-ring electrodes, are measured to extract the impedance parameters. The quadratic function models that relate the impedance parameters and the moisture contents of the kernels and husks are then established. Finally, based on these models, the dynamic moisture contents of husk-covered corn kernels in the field are measured from the corn dent stage to the maturity stage. Using this handheld device, the dynamic moisture content of kernels in husk-covered corn ears before physiological maturity can be measured nondestructively during different stages of kernel development in the field and the dehydration curve of the corn kernels can thus be obtained. Therefore, the proposed method can help us to determine the appropriate mechanized harvesting time and to screen the corn varieties that are suitable for high plant density and mechanized harvesting.
Section snippets
Measurement principle
As corn ears develop from the dent stage to the maturity stage, the moisture contents of the kernels, husks and cobs gradually decrease, and the dehydration rates of these parts of the ear are inconsistent: before physiological maturity, the husks dry rapidly to provide convenient conditions for post-maturity kernel dehydration (Kang and Zuber, 1989). Moreover, the dielectric properties of the kernels, the cobs and the husks are different. As the main constituents of a corn ear, water generally
Results of the husk-covered corn kernel layer moisture detection simulation
As shown in Fig. 6a and Fig. 6b, there are major differences in the horizontal electric field distributions of the double-ring electrodes under different corn ear moisture content conditions; the detailed numerical differences are listed in Table 5 and Table 6. In addition, for the geometric structural parameters of the sensing probe used in this case, the radial detection depth is within 10 mm (as shown in Fig. 6c), and the electric field mainly exists in the kernel and husk layers.
Table 5
Minimizing husk covering effects in kernel layer moisture detection
Several traditional agronomical indicators are used to estimate the corn ear maturity time, including the kernel moisture content, the kernel milk line position, and the formation of the kernel black layer; the corn kernel moisture content is the most frequently used indicator for maturity time prediction and determination of the mechanized harvesting time (Xu et al., 2019). In addition, before physiological maturity is reached, the husk can protect the developing kernels and also represents an
Conclusion
Our handheld device enabled nondestructive measurement of the dynamic moisture content of husk-covered corn kernels during the grain filling stage in the field using a quadratic regression model (where . This study will provide a new avenue for prediction of corn maturity time and a new instrument for breeding of corn varieties that are suitable for high plant density and mechanized harvesting. Regardless of whether the kernels are husk-covered or not, the ring electrodes can
CRediT authorship contribution statement
Li-Feng Fan: Methodology, Validation, Formal analysis, Investigation, Writing - original draft. Zhi-Qiang Chai: Validation, Formal analysis, Investigation. Peng-Fei Zhao: Writing - review & editing. Zong-Fu Tian: Investigation, Resources. Shi-Qian Wen: Validation, Investigation. Shao-Ming Li: Resources. Zhong-Yi Wang: Conceptualization, Methodology, Writing - review & editing, Supervision, Project administration. Lan Huang: Conceptualization, Methodology, Writing - review & editing,
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was supported by the National Natural Science Foundation of China [grant number 31771671], and the National Key Research and Development Program of China [grant numbers 2016YFD0300606 and 2016YFD0300304].
Reference (30)
- et al.
A new harvest time prognosis tool for forage maize production in Germany
Agr Forest Meteorol
(2005) - et al.
Nuclear magnetic resonance relaxation characterisation of water status of developing grains of maize (Zea mays L.) grown at different nitrogen levels
Journal of Bioscience and Bioengineering
(2014) - et al.
MIMYCS.Moisture, a process-based model of moisture content in developing maize kernels
European Journal of Agronomy
(2014) - et al.
Maize cob plus husks mimics the grain sink to stimulate nutrient uptake by roots
Field Crops Research
(2012) - et al.
Use of remote sensing to predict the optimal harvest date of corn
Field Crops Research
(2019) - et al.
Phenotyping maize for adaptation to drought
Front Physiol
(2012) - et al.
A Novel Handheld Device for Intact Corn Ear Moisture Content Measurement
IEEE Transactions on Instrumentation and Measurement
(2020) - et al.
Efficiency of utilization of a selection index in assessment of dry down of corn genotypes (Zea mays L.)
Scientific Papers-Series A, Agronomy
(2013) - et al.
Seed Development and Quality in Maize Cultivars
Not Bot Horti Agrobo
(2011) Corn Moisture Measurement Accuracy. T Asae
(1985)
Combining ability for grain moisture, husk moisture, and maturity in maize with yellow and white endosperms
Crop Science
An electronic probe for estimating ear moisture content of maize
Crop Science
Relationship between kernel drydown rate and resistance to gibberella ear rot in maize
Euphytica
Electrical properties of plant tissues: resistance of a maize leaf
Bulgarian Journal of Plant Physiology
Corn growth and development
Cited by (8)
Evaluation of a handheld near-infrared spectroscopy sensor for rapid corn kernel moisture estimation
2023, Crop, Forage and Turfgrass ManagementMeasurement of two-layer medium dielectric property using a novel parameters model in radio frequency
2023, International Journal of Circuit Theory and ApplicationsPlant Tissue Modelling Using Power-Law Filters
2022, Sensors