Effects of different tillage measures and organic manure application amount on soil phosphorus fractions in dry-land wheat fields

To explore the effects of tillage measures and organic manure application on soil phosphorus fractions in dry-land wheat fields, based on a long-term positioning experiment of tillage and fertilizer (since 2007) in the Loess Plateau, through using the soil phosphorus classification method of Tiessen, we have systematically studied the distribution characteristics of soil available phosphorus, total phosphorus and phosphorus fractions in 0−20 cm soil layer under four agronomic measures: deep tillage + chemical fertilizer (T), deep tillage + chicken manure + chemical fertilizer (TM), no tillage + chemical fertilizer (NT), and no tillage + chicken manure + chemical fertilizer (NTM). The results showed that 1) compared to T treatment, the soil available phosphorus content under NT treatment was increased by 58.37%, the available phosphorus and total phosphorus contents under organic fertilizer treatments (i.e., NTM and TM treatments) were higher than those under no organic fertilizer treatments (i.e., NT and T treatments). Compared with those under TM treatment, the available phosphorus and total phosphorus contents under NTM treatment were significantly increased by 11.43% and 43.41%, respectively. 2) Compared to T treatment, NT, NTM, and TM treatments improved the content of the active inorganic phosphorus fractions of NaHCO₃-Pi and moderate active inorganic phosphorus fractions of NaOH-Pi, especially under NTM and TM treatments. 3) Compared to T treatment, the contents of NaHCO₃-Po and NaOH-Po under NT treatment were increased by 53.07% and 55.56%, respectively. Compared to that of TM treatment, the above two fractions under NTM treatment were significantly increased by 90.84% and 60.31%, respectively. Compared to T treatment, the residual-P content under NT treatment was increased by 12.90%, and the Residual-P content under NTM treatment was increased by 36.60% compared to that of TM treatment. 4) A surplus of phosphorus fertilizer was applied each year in the 17 a long-term positioning test base, and the residual phosphorus mainly existed in the form of NaHCO₃-Pi, D.HCl-Pi, NaHCO₃-Po, and C.HCl-Po. No tillage and organic manure could promote the translation from stable phosphorus (C.HCl-Po) to active phosphorus (NaHCO₃-P) and potentially mobile phosphorus (NaOH-P). Partial least square (PLS) regression analysis indicated that NaHCO₃-Pi and NaOH-Pi were the most effective phosphorus sources and their contributions to wheat yield were high. The NTM treatment showed the most apparent effect in promoting the accumulation of the two phosphorus fractions. Therefore, no tillage and organic manure is an agronomic practice worth promoting in dry-land wheat fields in this area; however, reduction of chemical phosphate fertilizer application should be considered in the promotion and application.