Relay-intercropping soybean with maize maintains soil fertility and increases nitrogen recovery efficiency by reducing nitrogen input

Optimized nitrogen(N)management can increase N-use efficiency in intercropping systems.Legume-nonlegume intercropping systems can reduce N input by exploiting biological N fixation by legumes.Measurement of N utilization can help in dissecting the mechanisms underlying N uptake and utilization in legume-nonlegume intercropping systems.An experiment was performed with three planting patterns:monoculture maize(MM),monoculture soybean(SS),and maize-soybean relay intercropping(IMS),and three N application levels:zero N(NN),reduced N(RN),and conventional N(CN)to investigate crop N uptake and utilization characteristics.N recovery efficiency and 15N recovery rate of crops were higher under RN than under CN,and those under RN were higher under intercropping than under the corresponding monocultures.Compared with MM,IMS showed a lower soil N-dependent rate(SNDR)in 2012.However,the SNDR of MM rapidly declined from 86.8%in 2012 to 49.4%in 2014,whereas that of IMS declined slowly from 75.4%in 2012 to 69.4%in 2014.The interspecific N competition rate(NCRms)was higher under RN than under CN,and increased yearly.Soybean nodule dry weight and nitrogenase activities were respectively 34.2%and 12.5%higher under intercropping than in monoculture at the beginning seed stage.The amount(Ndfa)and ratio(%Ndfa)of soybean N2 fixation were significantly greater under IS than under SS.In conclusion,N fertilizer was more efficiently used under RN than under CN;in particular,the relay intercropping system promoted N fertilizer utilization in comparison with the corresponding monocultures.An intercropping system helps to maintain soil fertility because interspecific N competition promotes biological N fixation by soybean by reducing N input.Thus,a maize-soybean relay intercropping system with reduced N application is sustainable and environmentally friendly.

Using side-dressing technique to reduce nitrogen leaching and improve nitrogen recovery efficiency under an irrigated rice system in the upper reaches of Yellow River Basin, Northwest China

The excessive nitrogen （N） fertilizer input coupled with flood irrigation might result in higher N leaching and lower nitrogen recovery efficiency （NRE）. Under an intensive rice system in the Ningxia irrigation region, China, environmental friendly N management practices are hreavily needed to balance the amount of N input for optimum crop production while minimize the nitrogen loss. The objective of this study was to determine the influences of side-dressing （SD） technique in mechanical transplanting systems on the NRE, N leaching losses and rice yield in anthropogenic-alluvial soil during two rice growing seasons （2010-2011）. Four fertilizer N treatments were established, including conventional urea rate （CU, 300 kg ha-1 yr-1）; higher SD of controlled-release N fertilizer rate （SD1,176 kg ha-1 yr-1）; lower SD of controlled-release N fertilizer rate （SD2, 125 kg ha-1 yr-1）; and control （CK, no N fertilizer）. Field lysimeters were used to quantify drainage from undisturbed soil during six rice growing stages. Meanwhile, the temporal variations of total nitrigen （TN）, NO3--N, and NH4＋-N concentrations in percolation water were examined. The results showed that SD1 substantially improved NRE and reduced N leaching losses while maintaining rice yields. Across two years, the averaged NRE under SD1 treatment increased by 25.5% as relative to CU, but yet the rice yield was similar between two treatments. On average, the nitrogen loss defined as TN, NH4＋-N, and NO3--N under the SD1 treatment reduced by 27.4, 37.2 and 24.1%, respectively, when compared with CU during the study periods. Although the SD2 treatment could further reduce N leaching loss to some extent, this technique would sharply decline rice yield, with the magnitude of as high as 21.0% relative to CU treatment. Additionally, the average NRE under SD2 was 11.2% lower than that under SD1 treatment. Overall, the present study concluded that the SO technique is an effective strategy to reduce N leaching and increase NRE, thus potentially mitigate local environmental threat. We propose SD1 as a novel alternative fertilizer technique under an irrigated rice-based system in Ningxia irrigation region when higher yields are under consideration.

Recovery of Nitrogen and Phosphorous as Struvite From Swine Waste Biogas Digester Effluent

Objective To investigate the feasibility of nitrogen and phosphorus recovery from swine waste biogas digester effluent and the effects of pH and NH4^＋： Mg2^＋： PO4^3- molar ratio on its precipitation. Methods Precipitation experiments with swine waste biogas digester effluent were conducted at pH 7.5, 8.0, 8.5, and 9.0 together with NH4^＋： Mg^2＋： PO4^3- molar ratios 1： 0.2： 0.08, 1： 1： 1, and 1： 1.5： 1.5. Chemical and X-ray diffraction （XRD） analysis were done to determine the composition of the precipitate. Results The highest removal and recovery of NH4^＋ and PO4^3- were achieved at pH 9.0 in each experiment. The elevation of pH to 9.0 alone could decrease the initial PO4^3- concentration from 42 mg L^-1 to 4.7 mg L-1 and 89.2% PO4^3- recovery was achieved. The pH-molar ratio combination 9.0-1： 1.5： 1.5 effected 76.5% NH4^＋ and 68.5% PO4^3- recovery. The molar ratio of 1： 1： 1 together with pH elevation to 9.0 was determined to be the optimum combination for both NH4＋ and PO4^3- removal as it recovered over 70% and 97% of the initial NH4^＋ and PO4^3-, respectively. Conclusions Nitrogen and phosphorus can be recovered from biogas digester effluent as struvite.

Nitrogen recovery from wastewater using microbial fuel cells

Nitrogen is one of major contaminants in wastewater; however, nitrogen, as bio-elements for crop growth, is the indispensable fertilizer in agriculture. In this study, two-chamber microbial fuel cells （MFCs） were first operated with microorganisms in anode chamber and potassium ferricyanide as catholyte. After being success- fully startup, the two-chamber MFCs were re-constructed to three-chamber MFCs which were used to recover the NO-3 -N and NH＋4 -N of synthetic wastewater into value- added nitrogenous fertilizer from cathode chamber and anode chamber, respectively. Ferric nitrate was used as the sole electron acceptor in cathode, which also was used to evaluate the NO-3 -N recover efficiency in the case major anion of NO3 in cathode. The output voltage of these MFCs was about 600-700 mVat an external load of 500 Ω. About 47% NH＋4 -N in anode chamber and 83% NO-3 -N in cathode chamber could be recovered. Higher current density can selectively improve the recovery efficiency of both NH＋4-N and NO3 -N. The study demonstrated a nitrogen recovery process from synthetic wastewater using three-chamber MFCs.

Study on the Technologic Optimization for Hydrolysis of Silver carp By-products

The hydrolysis process for Silver carp by-products was studied. Protein hydrolysate was prepared with proteolytic enzyme, Alcalase. Hydrolysis conditions were optimized by the regression model of three factors five levels quadratic rotation perpendicular regressive design. The optimum hydrolysis conditions of hydrolyzing the protein of Silver carp by-products were determined to be concentration of enzyme (E/S) 3.33%, pH 8.54, hydrolyzing temperature 58 ℃, reaction time 90 min, concentration of substrate 8%. Nitrogen recovery was more than 75%.

Raceway pond cultivation of a new Arthrospira sp.ZJWST-S1 in digested piggery wastewater treated by MBR and ozonation

A new Arthrospira strain named Arthrospira sp.ZJWST-S1 was isolated from a local digested piggery wastewater(DPW)storage pool in Jiaxing City,Zhejiang Province,China.It possessed good stain resistance against contaminants in DPW,which was pretreated with a membrane bioreactor(MBR).The strain was identified as Arthrospira platensis(A.platensis)based on its morphological characteristics and the 16S rDNA sequencing analysis.The effect of chrominance on growth of A.platensis ZJWST-S1 was investigated in a field raceway pond filled with MBR effluent or MBR effluent decolorized with ozonation.After ozonation,the chrominance of MBR effluent was decreased from 700 mg Pt/L to 150 mg Pt/L.Two runs of cultivation showed that A.platensis ZJWST-S1 grew faster in the ozone decolorized MBR effluent,the averaged biomass concentration being 0.907 g/L after 10 days of cultivation,close to that in a Zarrouk medium(0.969 g/L).By comparison,the biomass grew much slower in the non-decolorized MBR effluent(0.624 g/L).The pollutant removal was also benefited from the accelerative growth of A.platensis ZJWST-S1 in the decolorized MBR effluent.Almost all ammonium,61.2%of nitrate and 68.1%of phosphate were removed by the A.platensis ZJWST-S1 in the decolorized MBR effluent,much higher than the corresponding values of almost all ammonium,25.4%of nitrate and 36.5%of phosphate in the MBR effluent.Furthermore,the Arthrospira biomass harvested from the ozone decolorized MBR effluent after 10 d cultivation was with crude protein content of 59.1%±3.5%in dry algae powder.The content of Pb,As,Cd and Hg in biomass was also low enough to meet the Chinese Arthrospira Standard for Animal Feed(GB/T 17243-1998).This study showed that the new strain A.platensis ZJWST-S1 possessed potential to be used for producing animal feed and simultaneous removal of nitrogen and phosphorus in DPW.