Economic Viability Of Enhanced Application Rates Of Humic ACID, Compost TEA, BONE Meal and ROCK Phosphate On Extractable Phosphorus Of Calcareous SOILS In Organic Farming Systems.

A greenhouse experiment was conducted at the University of Wyoming’s Laramie Experiment Station (Laramie, WY) to investigate how amendment application rates beyond manufacturer’s recommendations influence soil nutrient cycling and crop yield.  A loamy calcareous soil (0-15 cm) obtained from a field in cash crop production was air-dried and sieved to 2 mm prior to filling in pots (3000 cm³).  Pots containing 15 cm of sand at the bottom and were topped with 15 cm of sieved soil.  Each pot received five alfalfa seeds treated with Nitragin® Rhizobium inoculant and were thinned to one plant pot^-1 after emergence.  Alfalfa pots were completely randomized, rotated every other week and watered twice daily but did not receive supplemental fertilizer.  Once all pots were established, alfalfa plants were clipped to 2.5 cm and treatments applied.  Treatments included variable rates of humic acid, compost tea, bone meal, or rock phosphate (alone or in specific combinations) and an untreated control.  Individual plants were harvested at approximately 10% bloom and soil samples were collected from the top 15 cm portion of the pot.  No differences (P>0.05) were observed in alfalfa yield or dry matter content from any of the treated pots compared to controls.  Extractable phosphorus (P) did not differ (P > 0.05) among any of the treatments except with bone meal (3000 kg ha^-1), which provided significantly more (P<0.05) extractable P versus rock phosphate (600 kg ha^-1).  To further investigate the effects of these amendments on soil microbial activity, the same source soil from the greenhouse study was prepared for in-house incubations.  Three replicates each of 50 grams of soil was adjusted to 23% field capacity, amended and incubated in sealed Mason® jars for 14 days (25±2°C).  Soil was amended with either bone meal (3,000, 6,000 and 12,000 kg ha^-1), humic acid:rock phosphate (320 L ha^-1: 600 kg ha^-1), or rock phosphate (600 kg ha^-1), in addition to an untreated control.  Soils with bone meal developed heavy Actinomycetes growth on soil surfaces and had significantly lower (P< 0.05) pH versus the humic acid:rock phosphate, rock phosphate or control soils.  Conversely, soil electrical conductivity was significantly higher (P<0.05) in soil amended with bone meal at 12,000 kg ha^-1.  Applications of bone meal beyond manufacturer’s recommendations may encourage beneficial soil microbial growth in exchange for increasing soil EC, which may be detrimental to soil fertility over the long-term and does not significantly improve crop yields.