Complex sentence: The total production of hemp fiber in the United States had in 1933 decreased to around 500 tons/year, then cultivation of hemp began to increase 1934-1935 but still at very low volume compared with other fibers.
Split into simpler sentences: The total production of hemp fiber in the United States had in 1933 decreased to around 500 tons/year. Cultivation of hemp began to increase in 1934 and 1935 but was production remained at very low volume compared with other fibers.