A photo from the same publication of August 1st, 1938 showing an Army Type 94 Reconnaissance Aircraft or Nakajima Ki-4 liaise with ground troops.
The ground unit would set up two poles connected with a string at the top and a message canister hanging in the middle. The aircraft would make a very low pass and fish the canister with the message using a line with a hook operated by the rear observer. This was a most efficient, albeit rather primitive, method of communication at an age when the radio was not sufficiently developed. Reconnaissance aircraft like the Ki-4 and later the Tachikawa Ki-36 "Ida" would guide ground troops to their target or warn them of enemy units in the area during the Sino-Japanese War.
Any suggestions about the trucks in the photo?
The tail marking is not clear enough but the caption mentions that "after the fall of Xuzhou, Lanfeng and Kaifeng the next major target of our advancing troops is the city of Zhengzhou". From this information it is apparent that the photo was taken during the Battle of Northern and Eastern Henan province.
Monograph #96 mentions:
"Air Operations Over North China to Support the Wu-Han Operation
After the Tungshan Operation, the North China Area Army was charged primarily with keeping peace and order in the occupied areas.
In early August, when the North China Area Army Air Unit9 was organised, the Area Army commander ordered the Sudo Unit (one fighter squadron and two light bomber squadrons)10 to Anyang and Tungshan with the mission of gathering enemy intelligence and supporting the ground operations of the 1st Army garrison groups (the 5th and 114th Divisions and the 5th Independent Mixed Brigade garrisoning Shantung Province and the area around Tungshan, the 110th Division guarding the Peiping-Tienching sector and the Cavalry Group on the east side of the New Huang Ho).
9. The Order of Battle of the North China Area Army Air Unit was published on 2 August 1938. The unit was composed of the 3rd squadron of the 64th Air Regiment, 27th Air Regiment, 90th Air Regiment and two airfield battalions.
10. The original Japanese manuscript states that the Sudo Unit was composed of three air reconnaissance squadrons. This is incorrect. The unit, which was commanded by Col Einosuke Sudo, was composed of the 3rd Squadron, 64th Air Regiment (one fighter squadron) and the 27th Air Regiment (two light bomber squadrons)."
Ofcourse all this was from August after the publication of the magazine.
The 5th Rentai (Wing) moved to the China theatre in June 1938 with four chutai. In July the 1st and 2nd chutai became the 1st Daitai (Battalion) commanded by Col Shibata and equipped with Ki-4s (the 3rd & 4th chutai became the 2nd Daitai). On August 1st 1938 the 1st Daitai became the 27th Sentai, mentioned as 27th Air Regiment in Monograph.
Therefore this author believes that the photo was taken during operations of the 1st Daitai in July in the North Eastern China Area before it became 27th Sentai in August.