Disclaimer: this got a little long (cause I never write long posts...

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And perhaps rent or borrow a higher capacity truck for towing.
Your loaded trailer is getting towards double the weight of your actual vehicle (3589 - 4075lbs).
The max rated towing capacity is 5000 lbs for an X with an auto transmission and 3500 lbs for a manual transmission. The gen1 and the gen2 have the same capacity rating.
Know that there is no criticism in this post, just plain concern for your well being and a desire to get the info out there.
You are running a high risk of the brakes overheating, jack knifing and also for the trailer to drive you, meaning that the extra weight can make your brakes useless, but also if it starts to swing you will have no control over the direction your vehicle goes. A swinging load could also cause you to roll over. All of this happens a lot faster than most people think. You also have to recognize that the trailer hitch on the vehicle is only rated for a certain amount of weight. If you are only using a bumper ball, the towing capacity is greatly reduced due to the very real danger of the ball tearing out of the relatively thin bumper steel. I'd highly recommend a proper frame mounted trailer hitch with an appropriate rating.
You should also be sure to use safety chains, which will keep the trailer connected to you should the hitch ever fail. Once again, most common safety chains are only rated at about 3500 lbs, unless they were bought with/for a larger trailer. Safety chains also need an appropriate rating for the load they may possibly encounter.
Mechanically, you risk overheating not only your engine (which there is a light for), but the transmission, which there is no extra cooler or temp light for on the gen1. A blown transmission will be about a $5K bill (possibly more) to repair. Let's not talk about the liability/legal issues if you get into an accident with a vehicle that is well over the legal towing/carrying capacity, but you could end up having nowhere to take the hay to in the future.
Nissan strongly recommends that you use trailer brakes for larger loads (SUV's and heavy trailers).
Not trying to be the doom and gloom guy, but you're running a lot of risks that could affect yourself and others now, and well into the future.
If renting or borrowing a more appropriate vehicle is not in the cards you could try carrying a lighter load of hay and make more trips. I know that it may not be in the cards if the hay is in a large round bale vs a bunch of cubes or loose.
If you do continue as you are, please be sure to stay off any highways and use back roads only. If the highway patrol sees you, they will likely pull you over. Especially if you're swaying at all and if they see your trailer doesn't have lights (and possibly no license plate). Also, don't get cocky and don't rush. I wouldn't suggest going over 35 mph with that load, less on gravel. If you have kids, leave them at home. You don't need the distractions and if something happens you don't need the guilt (poop happens).