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

Abstract

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.

Soil properties and not inputs control carbon : nitrogen : phosphorus ratios in cropped soils in the long term

“…The P budgets were more differentiated, with the only positive budget observed in MI-NORG and the most negative in NON. The P budgets were similar to those shown by Oehl et al (2002) for the period 1978-1998 and by Keller et al (2012) for the period 1978-2007. Based on these P budgets, Oehl et al (2002) reported P transfers between horizons but no significant losses from the profile beyond 50 cm depth.…”

Soil phosphorus supply controls P nutrition strategies of beech forest ecosystems in Central Europe

“…Phosphatases hydrolyse different phosphate ester bonds to release inorganic P. Therefore, phosphomonoesterases cleave P from monoester forms, such as phospholipids or nucleotides, and phosphodiesterases release P from compounds like nucleic acids (Keller et al 2012;Paul 2015). Since plants secrete phosphodiesterase only under severe P deficiency, the enzyme is mainly produced by microorganisms (Turner and Haygarth 2005).…”

Soil Health and Related Ecosystem Services in Organic Agriculture

“…Microbial processes are involved in effective recovery of nutrients from manure and composted organic matter resulting in the release of essential plant nutrients during interactions with soil fauna, including earthworms (Bhadauria & Sazena, 2010). Higher levels of microbial activity in soil under organic managment may not necessarily lead to increased access to stable forms of phosphorus in organic matter (Keller et al, 2012). Re-use of organic 'wastes' (e.g.…”