Soil Phosphorus Management Based On Rhrizosphere Processes For Wheat And Maize In Intensive Cropping System

Exploring the biological potential of crop roots for efficient phosphorus (P) acquisition through rhizosphere manipulation is a promising strategy to reduce the overreliance on P fertilization, and thus to realize sustainable P management in intensive agriculture. However, it is not clear to what extent the biological potential of roots can be explored by soil P management which aims to optimize crop production. To address this question, the related studies focused on field-oriented experiments, supplemented by pot study, and combined the research methods from agronomy, root morphology, physiology and molecular biology to work on the following three topics:(1) manipulation of P supply on arbuscular mycorrhizal (AM) colonization and functioning in the field;(2) responses of root morphology, physiology and AM to P supply for wheat and maize;(3) effect of P supply on crop production and P efficiency for a wheat-maize rotation system. The main results were summarized as follows:(1) Three years field-oriented quantitative study proved the manipulation of soil P level on AM colonization for wheat and maize. The high limit of soil available P (Olsen-P) level for AM colonization differed with growth stages for wheat (32.2mg kg-1at GS31and26mg kg-1at GS65, respectively) but stabilized for maize (approximately22mg kg-1from V6to R1), which were generally higher than the critical soil P supply for plant growth (15.1mg kg-1at GS31and19.8mg kg-1at GS65for wheat, and11.6mg kg-1at V6and6.2mg kg-1at V12for maize, respectively). Under the critical soil P supply for plant growth, wheat maintained less than20%AM colonization at both GS31and GS65, while maize had increased AM colonization from50%at V6to60%at Rl.(2) In the field, P fertilization mainly increased soil available P level in the0-20cm soil layer. Correspondingly, root dry matter, root length and root surface area for wheat and maize were much higher at0-20cm soil depth than that at20-40cm soil depth; whereas AM colonization for both crops showed an increase at20-40cm soil depth. AM hyphae could enter the localized PVC chambers to acquire P, which was affected by P availability in bulk soil and PVC chamber soil, indicating that AM could help plants to obtain P from deeper soil depth.(3) In pot and field experiments, critical soil available P (Olsen-P) level for maize (NE15) best growth approximated4mg kg-1and the change-point indicating a significant increase of soil CaCl2-P was23.8mg kg-1. Correspondingly, the change-points for the responses of root morphology, AM colonization and expression of Phtl P transporters to soil available P coincided with or approached4mgkg-1.(4) In three-year field study, under different P application rates, wheat cultivars Shijiazhuang8and Kenong9204showed similar above-ground biomass and grain yield, with optimum P application rate being50-100kg P ha-1; Kenong9204had higher P uptake than Shijiazhuang8from GS31to GS65and at maturity. Althogh the two cultivars differed in their response patterns of root morphology, physology and AM colonization to P supply, the change-points of such responses coincided with or approached the optimum P supply for growth. Compared to Shijiazhuang8, Kenong9204had relatively better root morphology and higher expression of TaPHT1.2under all the P application rates.(5) During six years of wheat-maize rotation cropping, with increasing P application rates, wheat grain yield showed significant difference from the second year, with the optimum P supply being50-100kg P ha-1; maize grain yield had obvious difference from the fourth year, with the optimum P supply being12.5-25kg P ha-1; the total grain yield for this rotation system showed significant difference from the second year, with the optimum total P supply being75kg P ha-1. Under the optimum P supply, the accumulated P fertilizer use efficiency of this rotation system increased as planting years increased.In conclusion, this research indicated that root biological potential for efficient P acquisition could be regulated by soil P management, and relatively high potential could be maintained at or near the optimum P supply for best crop growth.