Phosphorus forms and enzymatic hydrolyzability of organic phosphorus in soils after 30 years of organic and conventional farming

• Published in: Journal of plant nutrition and soil science Vol. 175; no. 3; pp. 385 - 393
• Main Authors: Keller, Martina, Oberson, Astrid, Annaheim, Kathrin E., Tamburini, Federica, Mäder, Paul, Mayer, Jochen, Frossard, Emmanuel, Bünemann, Else K.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01-06-2012; WILEY‐VCH Verlag; Wiley-VCH
• Subjects: Agronomy. Soil science and plant productions; Biochemistry and biology; Biological and medical sciences; Chemical, physicochemical, biochemical and biological properties; enzymatic hydrolysis; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; long-term field experiment; manure; microbial biomass; Microbiology; Organic matter; Physics, chemistry, biochemistry and biology of agricultural and forest soils; sequential fractionation; Soil science; Soil-plant relationships. Soil fertility; Soil-plant relationships. Soil fertility. Fertilization. Amendments; Organic waste; Organic matter; manure; Inorganic element; Field experiment; Organic phosphorus; Sequential method; Soil science; Macronutrient(mineral); Fractionation; Enzyme; Biochemical compound; Conventional agriculture; long-term field experiment; Experimental study; Microbial biomass; Long term; enzymatic hydrolysis; Alternative agriculture; Hydrolysis; Soils; Organic agriculture; Enzymatic digestion; sequential fractionation; Field study
• ISSN: 1436-8730; 1522-2624
• DOI: 10.1002/jpln.201100177

Lower P‐input levels in organic than conventional farming can decrease soil total and available P, which can potentially be resupplied from soil organic P. We studied the effect of 30 y of conventional and organic farming on soil P forms, focussing especially on organic P. Soil samples (0–20 cm) were taken in a field experiment with a nonfertilized control, two organic systems receiving P inputs as animal manure, and two conventional systems receiving only mineral P or mineral P and manure. Soils were analyzed for total, inorganic, organic, and microbial P, by sequential P fractionation and by enzyme additions to alkaline soil extracts. Samples taken prior to starting the experiment were also analyzed. Average annual P balances ranged from –20 to +5 kg ha–1. For systems with a negative balance, labile and moderately labile inorganic P fractions decreased, while organic and stable inorganic P fractions were hardly affected. Similar quantities and proportions of organic P extracted with NaOH‐EDTA were hydrolyzed in all soils after addition of an acid phosphatase, a nuclease, and a phytase, and enzyme‐stable organic P was also similar among soils. Thus, neither sequential fractionation nor enzyme addition to alkaline soil extracts showed an effect of the type of applied P (manure vs. mineral) on organic P, suggesting that organic P from manure has largely been mineralized. Thus far, we have no indication that the greater microbial activity of the organic systems resulted in a use of stable P forms.