Impact of long-term fertilization, straw incorporation and liming on phosphorus fractions, availability and their interactions with soil properties in red soil

Investigating the contributions of different soil properties and their influences on changes in soil P fractions and availability is helpful for soil P management. Soil samples were collected in 2018 from a long-term red soil field experiment established in 1990. The unfertilized control (CK), chemical NK, NP, NPK, NPK with straw (S) (NPKS), NK + lime, NP + lime, NPK + lime, and NPKS + lime fertilization treatments, which were arranged in a randomized complete block design, were selected. Compared with no lime, lime addition significantly increased the labile P/total P ratio in the NPK and NPKS treatments by 12.35% and 11.75%, respectively. The results further revealed that fertilization treatments without lime application (NK, NP, NPK, and NPKS) significantly reduced the soil pH, Mehlich-3 (M3)-Mg and M3-Ca compared with those in the CK and lime treatments during 2018. In contrast, lime application reduced the M3-Fe and M3-Al concentrations by 2% and 3%, respectively. Long-term P fertilization improved soil organic matter, M3-P, M3-Fe, and M3-Al. While soil pH exhibited a strong and positive relationship with M3-Mg (r = 0.780**) and M3-Ca (r = 0.788**) and a strong and negative correlation with M3-Fe (r = -0.395*) and M3-Al (r = -0.584**), the transformation and discharge of various P pools in red soil were facilitated by soil OM, M3-Fe, and M3-Al as the key contributors. NPK and NPKS combined with lime addition could be useful approaches for increasing the available P (labile P/total P) by enhancing M3-Ca and M3-Mg and soil pH while reducing M3-Fe and M3-Al in red acidic soil.