Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/2/2012
Publication Date: 1/14/2013
Citation: Waldrip, H., He, Z., Griffin, T.S. 2012. Effects of organic dairy manure on soil phosphatase activity, available soil phosphorus, and growth of sorghum-sudangrass. Soil Science. 177(11):629-637.
Interpretive Summary: The number of organic dairies is growing in the Northeastern part of the United States. We do not know if the manure produced on organic dairies has the same fertilizer value as the manure from conventional dairies. This is because some properties of organic dairy manure are different from conventional dairy manure due to animal diet and farm management practices. In a greenhouse study, sudangrass was grown for 16 weeks in soil that contained either organic dairy manure, conventional dairy manure, or chemical fertilizer. Our goal was to figure out how organic dairy manure affects plant growth, the amount of soil phosphorus that is available for plant use, and the activities of some important enzymes in phosphorus cycling. The organic dairy manures were taken from 13 different farms in Maine, and they were very different in carbon, nitrogen, and phosphorus content. We found that the amount of plant growth did not change when plants received organic or conventional dairy manure, or chemical fertilizer. There was a lot of variability in plant growth with organic dairy manure, and plant growth was higher with manures that had less carbon relative to nitrogen and phosphorus. At the end of the study, there was more available phosphorus in soils that had manure than chemical fertilizer; but, there was no difference in available phosphorus in soil that had organic dairy or conventional dairy manures. Phosphatase activity was higher in soil that received organic dairy and conventional dairy manure than chemical fertilizer. This was related to the carbon to phosphorus ratio in organic dairy manure, where more carbon results in lower phosphatase activity.
Technical Abstract: Organic dairy (OD) production is increasing in the Northeastern U.S. due to consumer demand. Some physico-chemical properties of OD manure differ from conventional dairy (CD) manure, which could influence nutrient cycling and soil fertility differently when OD manure is applied to soil. Effects of OD manure on soil phosphatase activities [acid phosphomonoesterase (ACP), alkaline phosphomonoesterase (ALP), phosphodiesterase (PDE)], available soil phosphorus (P) and plant growth were investigated in a greenhouse study, where sorghum-sudangrass (Sorghum bicolor subsp. drummondii) was fertilized with manures from 13 Maine organic dairies, inorganic fertilizer, or CD manure. Soil phosphatase activities and Modified Morgan P were determined at planting, and after 16 weeks of plant growth. Plant biomass production did not differ (p > 0.05) between OD and CD manures, or inorganic fertilization. However, there was a wide range in biomass production with OD manure, which was negatively correlated to manure C:N and C:P (p < 0.05) ratios. After 16 weeks, OD manure amended soils had higher Modified Morgan P than soils that received inorganic fertilizer (p < 0.05), but there was no difference between OD and CD manured soils (p > 0.05). Of the three major soil phosphatases, ACP activity was highest, and increased with OD manure in a manner similar to CD manure. There was a negative correlation (p < 0.01) between ACP activity and OD manure C:P ratio, suggesting that manure C content influences P cycling and may reduce P availability in soils amended with OD manure, in a manner similar to CD manure.