Again I’m new just going off the research I’ve done and what is kinda working on this first indoor grow. But I also found this Horse manure and soil nitrogen. Horse manure is an abundant, locally available source of organic matter for soils. A major concern about horse manure is that it can cause a nitrogen deficiency when added to soils, leading to stunted, yellowed crops. Undiluted horse manure contains modest levels of nitrogen (about 1 to 2% of dry weight), and supplies small amounts of N to plants via slow release. When horse manure is mixed with woody bedding, the resulting product often ties up nitrogen in the soil through microbial immobilization, leading to N deficiency in the crop.