Generally, any tank over 119 gallons is a bulk tank requiring compliance with the federal hazardous materials rules to include placarding, licensing, shipping, etc. There are however, many exceptions to the regulations.
Basically, 49 CFR 173.5(a) and North Dakota state law state that a farm vehicle traveling on local roads between fields of the same farm and not carrying class 2 material is exempt from all HAZMAT requirements. So, a farm vehicle traveling township/county/state roads between farm fields does not have to meet HAZMAT requirements. However, if traveling on interstate highways or to a neighboring farm, the farm vehicle must comply with HAZMAT requirements because the movement does not meet the local roads/fields of the same farm exception.
The second part of the question pertains to an anhydrous ammonia nurse tank which is a class 2 material. 49 CFR 173.5 and North Dakota state law states that a farmer carrying class 2 materials is only exempt from subpart G and H (which includes training requirements and emergency response information requirements). So, a farm vehicle carrying anhydrous ammonia traveling on township/county/state roads is exempt from (1) training and emergency response information requirements in accordance with 49 CFR 173.5, (2) shipping paper requirements in accordance with 173.315(m), and (3) CDL HAZMAT endorsement requirements in accordance with 383.3(d). The vehicle does, however, have to be placarded/marked in accordance with 173.315(m).