为研究水稻浸种过程中种子的水分相态及其分布特征,利用低场核磁共振快速、无损、准确的检测技术,通过硬脉冲回波序列CPMG(carr purcell meiboom gill sequence)测量水稻种子横向弛豫时间T2,根据横向弛豫时间T2的差异区分种子内部的水分相态及其变化规律。试验结果表明:通过T2反演谱横向弛豫时间T2长短的差异,发现水稻浸种过程中种子内部水分存在结合水、自由水2种水分状态,同时可区分出内层水、中层水、外层水3种水分分层；二者均能通过回归方程合理的估测水稻在浸种过程中种子的吸水率情况；通过T2反演谱信号幅值大小的差异,发现水稻浸种过程中的种子总水含量不断上升,但由于判定依据及划分方式的不同,二者在水分的流动方式上略显差异。低场核磁共振技术对水稻浸种过程中种子内部的水分变化进行了直观的揭示,提供了一种高效的种子水分检测方法。

Nuclear magnetic resonance(NMR) is a fast, nondestructive and accurate test technique, which can be used to study the phase and distribution characteristics of moisture in rice seed during the soaking process.In this paper, the transverse relaxation time T2 has been analyzed by Carr Purcell Mei boom Gill(CPMG) pulse sequence.Thephase and change rules of moisture in rice seed are distinguished according to the different transverse relaxation time T2 in the T2 inversion spectrum.Samples of rice seed(variety was Shennong 9903)were obtained from Rice Research Institution, Shenyang Agricultural University in 2014.The mass of 10 seeds was determined as one sample with the total weight of 0.251 g, and there were 120 samples that were used in the present paper.The central frequency and the width of pulse of the magnetic field were searched by free induction decay(FID) pulse sequence, and all test samples were put in the low field NMR instrument one by one.All the tests were conducted by 4 times.The initial moisture content of the seeds was analyzed by NMR and the average transverse relaxation time T2 of rice seed was determined by CPMG pulse sequence.Test samples after data acquisition were soaked in water; the soaking time was ranging from 1 to 6h under standard laboratory conditions(20 ℃).After wiping the surface water of test samples with absorbent paper, the soaked samples were put in the NMR instrument again for data collection, and each test was repeated by 4 times.The spin echo signals collected by the repeated tests were valuated by the NMR inversion fitting software, and the average value of the inversion results was taken as the relaxation time and the signal amplitude of the sample.All the experimental data were statistically analyzed and expressed by mean ± standard deviation, and the results were analyzed by the regression analysis.The comparative dispersion of the data were obliterated according to the composition of the samples, the NMR equipment and the different measurement parameters.The test results showed that the low field NMR technique could be used for the analysis of the component,distribution and content of rice seed moisture during the soaking process.The results also showed that the value of T2 could indicate moisture component and phase state and the value of moisture signal amplitude(A2) could reflect the distribution of moisture.Moisture stratification and phase state could be evaluated by changing the number of iterations in the inversion fitting procedures.The experimental results showed that: the internal moisture of seed could be divided to bound water and free water during the soaking process according to the different transverse relaxation time T2.Moisture stratification of seed could also be divided into inner moisture, middle moisture and outer moisture.It could be seen that the moisture absorption ratio of rice seed could be reasonably estimated by the regression equation of 2 moisture states and moisture stratification.It was found that the total moisture content was kept increasing in the soaking process according to the difference of signal amplitude in the T2 inversion spectrum, while the movement of moisture was a little different due to different determination basisand classification.Low field NMR technique has 2 advantages: the first one is it reveals the moisture variation more intuitively during seed soaking, the second one is itreveals the moisture transfer more dynamically during seed soaking, and thus it provides an efficient detection method for the determination of the moisture content of seeds.

S351.5+1

国家高技术研究发展计划(863 计划):作物生产智能监控关键技术与系统研究(2012AA10A503)；国家重大科学仪器设备开发专项“便携式植物微观动态离子流检测设备研发与应用”(2011YQ080052)；公益性行业(农业)科研专项“作物育种材料农艺性状信息高通量获取与辅助筛分技术”(201203026)