基于K-means聚类算法的草莓灌溉策略研究

为进一步提高日光温室封闭式栽培下草莓灌溉水肥利用率,研究了基质含水率和温度影响下的草莓灌溉策略优化方法。采用土壤水分传感器对草莓果期基质含水率进行实时监测,通过对基质含水率随时间变化的规律分析,并结合日平均温度进行K-means聚类分析,提出一种草莓优化灌溉策略。试验结果表明,灌溉第1阶段基质含水率快速上升,在灌溉结束时达到峰值,每次灌溉基质含水率平均提高21.5个百分点;第2阶段快速下降,在20 min内基质含水率平均下降3.5个百分点;第3阶段变化趋于平稳,在30 min内基质含水率平均下降1.2个百分点。在每个灌溉周期内,含水率呈线性下降趋势,在整个果期内,其斜率随日平均温度的升高逐渐增加,由0.0114增加至0.0365。研究结果表明,根据基质含水率变化和日平均温度区间进行定量灌溉,理论上果期每株草莓仅需要4.51 L水,可节水15.4%,该方法能有效提高水肥利用率,实现节水节肥。

Investigation of Strawberry Irrigation Strategy Based on K-means Clustering Algorithm

Substrate cultivation is the development direction of greenhouse cultivation mode,and it is of great significance to study the modern precision irrigation method for substrate cultivation.On-demand irrigation is one of the main methods of modern precision irrigation.It is inseparable from real-time monitoring and feedback of water content.The water content is an important parameter in modern precision irrigation methods.Moisture sensor based on the principle of frequency domain reflection(FDR)was used in a substrate environment for monitoring water content.The moisture detection module of JZH-0 sensor adopted the principle of FDR,which had good performance on the soil moisture testing.However,it needed to be calibrated before using in different kinds of substrate.In order to further optimize the closed cultivation irrigation method in solar greenhouse and improve the water and fertilizer utilization rate,based on the theoretical research of on-demand irrigation,the existing integrated irrigation system of water and fertilizer,air temperature sensor and soil moisture sensor were mainly used for irrigation and real-time data monitoring and collection.The study on the irrigation strategy of closed greenhouse cultivation of strawberry in greenhouse was carried out by collecting the moisture content of the substrate under the experience of irrigation and the temperature in the greenhouse.The variation of moisture content of substrate in different time scales was firstly summarized.The result showed that the substrate water content of each irrigation rose rapidly,reaching a peak at the end of each irrigation time,with an average increase of about 21.5 percentage points;the second stage decreased rapidly,with an average decrease of 3.5 percentage points in 20 min;the third stage of the trendwas stabilized,with an average decrease of 1.2 percentage points in 30 min.During each irrigation cycle,the water content of the substrate showed a linear downward trend,and the slope of the substrate could better reflect the daily variation of the matrix moisture.During the whole fruiting period of strawberry,the slope was increased with the increase of daily average temperature,which was increased from 0.0114 to 0.0365,reflecting the positive significance of temperature increase on crop water demand.Then,the daily variation of the moisture content of substrate was approximated to the daily water requirement of the crop to study the water requirement of the crop.Among the many factors affecting the water demand of crop,temperature with convenient measurement and high accuracy was chosen as the independent variables,because its influence effect was obvious and had strong coupling relationship with light intensity and relative humidity of air.The data was classified by K-means clustering algorithm.According to the classification results,an interval quantitative automatic irrigation strategy based on daily average temperature was proposed in closed greenhouse cultivation:three temperature intervals were set(13,18]℃,(18,22.5]℃,(22.5,27)℃and in turn corresponded to the daily variation of water content of three substrates as 0.88 percentage points,1.76 percentage points and 2.63 percentage points,respectively;calculating the daily average temperature of the day,and selecting the appropriate daily variation of moisture content of substrate according to the temperature range to which it belonged and irrigated the next day;it was revised on Monday in a weekly cycle.Theoretically only 4.51 L water was needed per strawberry plant in fruit stage,which can save 15.4%water.Under this strategy theoretically based on K-means clustering algorithm,the water and fertilizer utilization were effectively improved,and the closed greenhouse irrigation methods in solar greenhouses were further enhanced.