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Short-chain polyphosphate fertilizers have been increasingly applied in agriculture, but little is known about the chemical behaviors of polyphosphate in soils. Herein, a cylinder experiment was carried out to investigate the influences of different P types (i.e., mono-ammonium phosphate (MAP), phosphoric acid (PA) and ammonium polyphosphate (poly-P)) and their application methods (single vs split) on the mobility and availability of P in soil through a column millimeter-scale slice cutting method; meanwhile a soil microcosm experiment (560-day) was conducted to investigate the effects of different P types on phosphorus dynamic transformation. Polyphosphate addition significantly increased P mobility. The average distance of P downward movement (81.5 mm) in soil profile in the poly-P application treatment increased by 33.6% and 81.1%, respectively, compared to the MAP and PA treatments. Different P application methods also markedly influenced phosphorus mobility. For instance, the average distance of P vertical movement in the split P application treatment was 21.2% higher than in the single application treatment, indicating that split P addition significantly increased P downward movement. Moreover, polyphosphate application decreased soil P fixation by blocking the transformation of the applied-P from labile to recalcitrant forms (HCl-P and residual-P). Overall, our findings provide meaningful information to current phosphorus fertilization practice in increasing soil P mobility and bioavailability. We suggest that polyphosphate could be regarded as an alternative P source used in agriculture, and split polyphosphate application is recommended as an effective P fertilization strategy.

Rhizobia are bacteria well known for biological nitrogen fixation through symbioses. These bacteria may also perform as plant growth promoting rhizobacteria (PGPR). In this study the role of rhizobia as PGPR was studied. Rhizobia was isolated from the root nodules of various summer legumes including Glycine max (Soybaen), Vigna radiata (Mung bean), Vigna unguiculata (Cowpea), Susbenia grandiflora (Sesbania) and Cymposistetra gonoloba (Guar) grown at New Developmental Farm (NDF), the University of Agriculture Peshawar, Pakistan during summer 2011. Rhizobia were isolated from root nodules by using yeast minitol agar media, pure culture of each isolate was prepared and examined for various PGPR traits. Data revealed that 9, 83, 47 and 21% of tested strains were found to produce cyanide (HCN), siderophores, indole-acetic acid (IAA) and solubilized phosphorus respectively. Among the tested rhizoial isolates, rhizobia isolated from Vigna radiata showed highest PGPR activity fallowed by Glycine max while relatively lower PGPR activity was observed for rhizobial isolates of Cymposistetra gonoloba (Guar). All the tested isolates were gram negative. Soybaen and cowpea isolates were found to be fast growing while mung bean, susbenia and guar were slow growing in nature. This study indicates that rhizobial isolates of Vigna radiata and Glycine max have the capability to be used as PGPR.

BACKGROUND Nitrification inhibitors (NIs) and urease inhibitors (UIs) can decrease the risk of nitrogen (N) loss and extend N uptake by plants. However, there are few case studies about reduced N application combined with double inhibitors (DIs, NI plus UI), especially under drip irrigation systems. A 2‐year field experiment was therefore conducted to explore the effect of 80% N application rate combined with NI or DIs on soil N transformation, wheat productivity and N use efficiency (NUE) in a drip‐irrigated field. The four treatments included a no‐fertilizer control, 100% urea, 80% urea + NI (nitrapyrin) and 80% urea + DIs (nitrapyrin and N‐(n‐butyl) thiophosphorictriamide (NBPT)). RESULTS Our results showed that the 80% urea + DIs treatment significantly increased the ratio of NH4+ to NO3− and N content (urea‐N, NH4+‐N and NO3−‐N) in soil at 0–20 cm depth (P < 0.05) at the heading stage and the filling stage of wheat in both 2013 and 2014, relative to the 100% urea treatment. A total of 80% urea + NI treatment decreased wheat N uptake and wheat productivity (plant biomass and yield) compared to 100% urea treatments (P < 0.05). However, application of 80% urea combined with DIs achieved equivalent wheat productivity with 100% urea treatment. Moreover, the greatest NUE (43.6%) was recorded with the application of DIs. CONCLUSIONS Cutting the N application rate by 20% combined with NBPT and nitrapyrin could provide a sustainable fertilization strategy for wheat production under drip irrigation. © 2020 Society of Chemical Industry