Exogenous phosphorus compounds interact with nitrogen availability to regulate dynamics of soil inorganic phosphorus fractions in a meadow steppe

Heyong Liu, Ruzhen Wang, Hongyi Wang, Yanzhuo Cao, Feike A. Dijkstra, Zhan Shi, Jiangping Cai, Zhengwen Wang, Hongtao Zou, Yong Jiang
2019 Biogeosciences Discussions  
<p><strong>Abstract.</strong> Here we investigated the effects of P compounds (KH<sub>2</sub>PO<sub>4</sub> and Ca(H<sub>2</sub>PO<sub>4</sub>)<sub>2</sub>) with different addition rates of 0, 20, 40, 60, 80 and 100&amp;thinsp;kg&amp;thinsp;P&amp;thinsp;ha<sup>&amp;minus;1</sup> yr<sup>&amp;minus;1</sup> and NH<sub>4</sub>NO<sub>3</sub> addition (0 and 100&amp;thinsp;kg&amp;thinsp;N&amp;thinsp;ha<sup>&amp;minus;1</sup>&amp;thinsp;yr<sup>&amp;minus;1</sup>) on soil labile (Olsen-P),
more » ... en-P), moderate-cycling and recalcitrant inorganic phosphorus (IP) fractions in a calcareous grassland of northeastern China. Soil moderate-cycling IP, not readily available to plants but transforming into available P quickly, include variscite (Al-P), strengite (Fe-P), dicalcium phosphate (Ca<sub>2</sub>-P) and octacalcium phosphate (Ca<sub>8</sub>-P); recalcitrant fractions include hydroxylapatite (Ca<sub>10</sub>-P) and occluded P (O-P). Soil labile and moderate-cycling IP fractions and total P significantly increased with increasing P addition rates, with higher concentrations detected for KH<sub>2</sub>PO<sub>4</sub> than for Ca(H<sub>2</sub>PO<sub>4</sub>)<sub>2</sub> addition. Combined N and P treatments showed lower moderate-cycling IP fractions compared to ambient N conditions due to enhanced plant productivity. Moderate-cycling IP was mainly regulated by aboveground plant biomass with KH<sub>2</sub>PO<sub>4</sub> addition, while by soil pH and plant biomass with addition of Ca(H<sub>2</sub>PO<sub>4</sub>)<sub>2</sub>. Ca(H<sub>2</sub>PO<sub>4</sub>)<sub>2</sub> addition significantly increased the soil recalcitrant IP (Ca<sub>10</sub>-P) fraction, while KH<sub>2</sub>PO<sub>4</sub> addition showed no impact on it. A significant positive correlation was detected between soil moderate-cycling IP fractions and soil Olsen-P which illustrated that moderate-cycling IP fractions were important sources for available P. Our results suggest that moderate-cycling IP fractions are essential for grassland P biogeochemical cycling and chemical form of P fertilizer should be considered during fertilization management for maintaining soil available P.</p>
doi:10.5194/bg-2019-173 fatcat:yr4kuyvrgrfyjh5b2ddneqzkeq