Time Series Analysis of Soil Water Content in the Shallow Zone under No-Till and Tilled Management Systems.

The knowledge of temporal variations of soil water storage in agricultural lands becomes useful in irrigation scheduling and certain management practices such as application of fertilizers. Processes such as preferential flow, which contributes to the rapid groundwater pollution, also changes with time influencing the soil water content in the soil profile. The temporal behaviour of the soil water regime in the vadose zone may provide indications of existence of such processes, and therefore the ability to predict the profile soil water content in advance becomes very important.

Soil water content in the shallow zone of the soil profile was measured hourly over two consecutive growing seasons along transects located on two adjoining plots with different soil management practices, no-till and till, by placing soil water sensors horizontally in a rectangular grid. The daily average water contents were calculated for each vertical array of soil water sensors and the resulting time series was analysed for autocorrelation and power spectral density.

The time series analysis indicated that the daily average water content along the vertical columns along the transects represent nonstationary time series whereas the autocorrelation functions of the differenced data converged rapidly indicating stationary nature of the transformed data with time and the possibility of fitting a time series model to predict the daily averaged water contents.