Application of cosmic-ray fast neutron method in soil moisture measurement of typical farmland in North China Plain.

Cosmic-ray neutron sensing (CRNS) is a new method for measuring mean soil moisture at regional scale. On the basis of continuous observation data of CRNS and the measurements of soil moisture with the distributed sensor network in Yucheng Comprehensive Experimental Station of the Chinese Academy of Sciences, we examined the applicability of the CRNS method to the agroecosystem in North China Plain. The stability of the neutron number in dry conditions (N0) and the effects of rainfall and irrigation on soil moisture estimation were investigated. The results showed that N0 was significantly affected by the underlying surface. The changes of N0 corresponded well to the planting and harvesting time of winter wheat and summer maize. Soil moisture estimated by the CRNS method had obvious response to rainfall and irrigation. When irrigation or rainfall occurred, soil moisture was overestimated. The CRNS method could effectively estimate regional soil moisture for the agroecosystem in North China Plain. The estimates of soil moisture were closest to the soil moisture in 10 cm depth.