[Characterization of Phosphorus Forms in Organic Composts and Their Effects on Leaf Phosphorus Content of Castanea mollissima in Chinese Chestnut Producing Area]

Abstract

Characterization of the forms of phosphorus (P) in four organic composts including compost of hulls and leaves of Castanea mollissima, edible fungi residues, corn stalks and chicken manure (BYZ), compost of edible fungi residues and chicken manure(ZF), composts of hulls and leaves of C. mollissima, edible fungi residues and chicken manure (BZ1 and BZ2) in Chinese chestnut producing area was conducted by sequential P fractionation developed by Dou et al. Field trial was conducted to study the effects of compost application on leaf phosphorus content of Castanea mollissima. The results showed that total phosphorus content(TP) of organic composts ranked as follows:BZ1(10.61 g·kg^-1) > ZF(9.03 g·kg^-1) > BYZ(8.56 g·kg^-1) > BZ2(7.68 g·kg^-1), and the inorganic phosphorus(P_i) accounted for 62.88%-73.62% of the total phosphorus in the organic composts. The content and proportion of HCl-P in the total fractionated phosphorus(P_rt) was the highest among P forms in ZF, while that of H₂O-P was the highest in BYZ, BZ1 and BZ2. The content of NaOH-P was very low in all the composts. Active H₂O-Por NaHCO₃-P had the highest inorganic phosphorus proportion(89.17%-96.00%) of all the P forms. The major P_iforms in BZ2 were H₂O- and HCl-extractable P fractions, while H₂O-P_i, HCl-P_i and NaHCO₃-P_i were major P_i forms in BYZ, BZ1 and ZF. Residual-P was the predominant organic phosphorus form, and BZ2 showed the highest Residual-P proportion of the total fractionated phosphorus(P_rt) among all the composts. Leaf phosphorus contents per unit area of Castanea mollissima by field trial on the added phosphorus-equivalent basis were expressed as:BZ2>BZ1>BYZ>ZF>CK. Increment of leaf phosphorus content per unit area in Julyand per month on average showed positive relationship with the content and proportion of H₂O-P_i in the total fractionated phosphorus of composts, which presumably played a key role in leaf phosphorus absorption of C. mollissima measured in the year of deep concentrated fertilization. The results suggested that composts of hulls and leaves of C. mollissima, edible fungi residues and chicken manure (BZ2) was a good choice in given area for aerobic composting raw material system in which organic wastes from Chinese chestnut industry accounted for 80% (hulls and leaves of Castanea mollissima and edible fungi residues accounted for 60% and 20% respectively), which had a high proportion of H₂O-P_i and organic Residual-P pool and led to the highest leaf phosphorus content of C. mollissima.

Keywords: Castanea mollissima producing area; leaf phosphorus content; organic compost; phosphorus forms.