The spec sheet says 30.4 PTO horsepower at 2700rpm. Note, this is a Electro-hydraulic independent PTO which by all accounts have lower HP ratings than a live or non-live PTO. That said, the new Yanmars seem to lose one or two rated HP on top of that when comparing other brands of 40hp tractors with independent hydraulic PTOs.
Here's where I'm going to start thinking out loud, so anyone reading this, please correct me if I'm off base. That PTO HP rating is from a Dynometer hooked up to the PTO, however, no torque ratings are published. What we do know is Yanmar engines have a shorter stroke and larger bore than other 40hp engines like Kubota and Kioti, which share the same 83mm bore and 92.4 mm stroke. Looking at the power bands of the two different 40hp engines, the Yanmar 4tnv88 puts out more torque than the Kubota 40hp at 2700rpm. So I'm wondering if the Yanmar has a slight PTO torque advantage whereas the smaller bore, longer stroke engines have a slight HP advantage?
In any event, if we get this detailed into PTO horsepower we're probably splitting hairs. You maybe just want to review the implement capacities page in the Yanmar LX tractor manual, it will tell you what size and weight mower, tiller, etc the tractor is rated to handle. My 45hp HST Yanmar, for example, has 32.5 PTO horsepower and is rated for 72 inch mowers and 74 inch tillers.