Phosphorus uptake from struvite is modulated by the nitrogen form applied

Next to nitrogen, phosphorus (P) is the most limiting nutrient for plant production worldwide. To secure food production, new nutrient management strategies using alternative P sources instead of mined P fertilizers need to be implemented. Struvite (MgNH₄PO₄ · 6 H₂O) is a promising example of a recycled mineral P fertilizer. Besides positive agronomic results regarding crop yields, further investigations are required to improve the use efficiency of the product and thereby increase its value. Using an automated plant phenotyping platform, we investigated the dynamic response to struvite by two plant species (lupine and maize) with diverse P acquisition strategies in an acidic sandy substrate. Although at three weeks after germination both maize and lupine had reduced leaf area in the struvite treatments compared to the commercial triple superphosphate (TSP), from week four onwards struvite plants grew larger than the TSP‐treated plants, indicating a slow release fertilizing effect. Greater P uptake efficiency (g / root length), but reduced root length were observed in the combined treatment of struvite and ammonium, in comparison to struvite and nitrate. We propose that rhizosphere acidification in response to ammonium uptake may enhance P recovery from struvite. A possible additional acidification effect by lupine root exudation might explain the higher P uptake efficiency in this species compared to maize. We conclude that struvite combined with ammonium can be used as a sustainable slow‐release P fertilizer on acidic sandy soils.     

接种丛枝菌根真菌和巨大芽孢杆菌的红三叶草对难溶磷的利用

A pot experiment was conducted to investigate the mobilization of sparingly soluble inorganic andorganic sources of phosphorus (P) by red clover (Trghlium pmtense L.) whose roots were colonized by the arbuscular mycorrhizal (AM) fungus Glomus mosseae and in association with the phosphate-solubilizing (PS) bacterium Bacillus megaterium ACCC10010. Phosphate-solubilizing bacteria and rock phosphate hada synergistic effect on the colonization of plant roots by the AM fungus. There was a positive interaction between the PS bacterium and the AM fungus in mobilization of rock phosphate, leading to improved plant P nutrition. In dual inoculation with the AM fungus and the PS bacterium, the main contribution to plant P nutrition was made by the AM fungus. Application of P to the low P soil increased phosphatase activityin the rhizosphere. Alkaline phosphatase activity was significantly promoted by inoculation with either the PS bacterium or the AM fungus.     

水分状态、土壤类型和氮素种类对氧化亚氮和甲烷排放的影响

Specific management of water regimes, soil and N in China might play an important role in regulating N2O and CH4 emissions in rice fields. Nitrous oxide and methane emissions from alternate non-flooded/flooded paddies were monitored simultaneously during a 516-day incubation with lysimeter experiments. Two N sources （^15N-（NH4）2SO4 and ^15N-labeled milk vetch） were applied to two contrasting paddies： one derived from Xiashu loess （Loess） and one from Quaternary red clay （Clay）. Both N2O and CH4 emissions were significantly higher in soil Clay than in soil Loess during the flooded period. For both soil, N2O emissions peaked at the transition periods shortly after the beginning of the flooded and non-flooded seasons. Soil type affected N2O emission patterns. In soil Clay, the emission peak during the transition period from non-flooded to flooded conditions was much higher than the peak during the transition period from flooded to non-flooded conditions. In soil Loess, the emission peak during the transition period from flooded to non-flooded conditions was obviously higher than the peak during the transition period from non-flooded to flooded conditions except for milk vetch treatment. Soil type also had a significant effect on CH4 emissions during the flooded season, over which the weighted average flux was 111 mg C m^-2 h^-1 and 2.2 mg C m^-2 h^-1 from Clay and Loess, respectively. Results indicated that it was the transition in the water regime that dominated N2O emissions while it was the soil type that dominated CH4 emissions during the flooded season. Anaerobic oxidation of methane possibly existed in soil Loess during the flooded season.     

Phosphorus fractions in poultry litter as affected by flue‐gas desulphurization gypsum and litter stacking

Previous research has shown that the addition of flue‐gas desulphurization (FGD) gypsum to poultry litter decreases water‐soluble P. No information is currently available, however, on extractable P fractions in poultry litter and P availability as affected by gypsum. The first objective of this work was to evaluate the effect of incubation time and rate of gypsum addition to litter alone or litter mixed with soil on total P and inorganic P in sequential extracts of H₂O, 0.5 m NaHCO₃, 0.1 m NaOH and 1 m HCl. Poultry litter was mixed with 25, 50, or 75% gypsum (by weight) and incubated alone or mixed with soil for 63–93 days at 25 °C, with periodic sequential extractions. For litter alone or litter mixed with soil, adding gypsum decreased total P and inorganic P in the H₂O fraction and increased both P forms in the NaHCO₃ fraction. These changes did not affect plant P availability as measured by Mehlich‐1 P. Increasing incubation time decreased total P and inorganic P in the H₂O fraction of litter alone or litter mixed with soil, which was apparently caused by P immobilization by fungi. A second objective of this study was to evaluate P in the H₂O and NaHCO₃ fractions of litter as affected by stacking time and depth. Litter was stacked to a height of 1.2 m with samples taken immediately after stacking and 31 days later to be sequentially extracted for total P and inorganic P. Stacking time did not affect P in the H₂O fraction, but it increased P in the NaHCO₃ fraction by 25%. These results suggest that stacking poultry litter may increase the amount of labile P.     

Soil phosphorus dynamics in a Vertisol as affected by cattle manure and nitrogen fertilization in soybean‐wheat system

Repeated application of phosphorus (P) as superphosphate either alone or in conjunction with cattle manure and fertilizer N may affect the P balance and the forms and distribution of P in soil. During 7 years, we monitored 0.5 M NaHCO₃ extractable P (Olsen‐P) and determined the changes in soil inorganic P (P_i) and organic P (P_o) caused by a yearly dose of 52 kg P ha^—1 as superphosphate and different levels of cattle manure and fertilizer N application in a soybean‐wheat system on Vertisol. In general, the contents of Olsen‐P increased with conjunctive use of cattle manure. However, increasing rate of fertilizer nitrogen (N) reduced the Olsen‐P due to larger P exploitation by crops. The average amount of fertilizer P required to increase Olsen‐P by 1 mg kg^—1 was 10.5 kg ha^—1 without manure and application of 8 t manure reduced it to 8.3 kg ha^—1. Fertilizer P in excess of crop removal accumulated in labile (NaHCO₃‐P_i and P_o) and moderately labile (NaOH‐P_i and P_o) fractions linearly and manure application enhanced accumulation of P_o. The P recovered as sum of different fractions varied from 91.5 to 98.7% of total P (acid digested, P_t). Excess fertilizer P application in presence of manure led to increased levels of Olsen‐P in both topsoil and subsoil. In accordance, the recovery of P_t from the 0—15 cm layer was slightly less than the theoretical P (P added + change in soil P — P removed by crops) confirming that some of the topsoil P may have migrated to the subsoil. The P fractions were significantly correlated with apparent P balance and acted as sink for fertilizer P.     

Soil organic carbon and nitrogen fractions and water‐stable aggregation as affected by cropping and grassland reclamation in an arid sub‐alpine soil

This paper investigates effects of cropping abandonment and perennial grass growing on soil organic C and N pools and aggregate stability, by comparing soils under native grassland, crop cultivation, perennial grass growing and cropping abandonment, in degraded cropland at a sub‐alpine site in north‐western China. The pools of total and particulate organic C (115 and 37 Mg ha⁻¹) in the 0–30 cm soil layer of native grassland were reduced by 31 and 54% after 30 years of crop cultivation. After 4 years of conversion from cropland to perennial grass growing total and particulate organic C pools were increased by 29 and 56%, whereas 4 year cropping abandonment increased particulate organic C by 36%. Rapid increases in total and particulate N were also found in perennial grass growing and cropping abandonment soils. The native grassland soil and soils of cropping abandonment and perennial grass growing had higher carbohydrate C concentrations in the 0–10 cm layer than the cropped soil. The rapid recovery of particulate organic fraction and carbohydrates in the re‐vegetated soils were probably due to higher plant biomass inputs and lower organic matter decomposition compared with those in the cropped soil. Aggregate stability of the 0–30 cm soil layer was significantly decreased by crop cultivation but showed a good recovery after 4 year re‐vegetations. This study suggests that reduction of soil organic matter and aggregate stability under crop cultivation may be remedied by cropping abandonment or perennial grass growing. Copyright © 2008 John Wiley & Sons, Ltd.