Supplementary Materials

Controlling nitrogen migration through micro-nano networks

Dongqing Cai1,2, Zhengyan Wu1,2, Jiang Jiang1,2, Yuejin Wu1,2, Huiyun Feng1,2, Ian G. Brown3, Paul K Chu4, Zengliang Yu1,2*

*Correspondence to: .

Supplementary Figures:

Supplementary figure 1.SEM images of loss control urea (LCU) components.a,Polyacrylamide (P) molecular assemblies formed through hydrogen bonds, showing a wicker-like morphology with fractal structure. b, Urea (U) molecular assemblies with networks appearance. c and d, U-P((0.9 gU + 0.002 gP)/L) with centipede-like structure. e and f, U-ATP ((0.9 gU + 0.1 gATP)/L) in which the ATP was well dispersed.

Supplementary figure 2.ATP (1 g/L) morphology and aggregate state.a-f, SEM images of ATPalone under different pH conditions (1, 3, 5, 7, 9 and 12).ATP alone tends to aggregate to bunches, and the dispersion increases with pH. g, ATPprecipitation behavior different pH conditions (1, 3, 5, 7, 9 and 12). h, Zeta potential of ATP under different pH conditions. The precipitation amount decreased with increasing pH due to the zeta potential (absolute value) effect of ATP.

Supplementary figure 3. Morphology of LCU in sand affected by leaching. a,b,Digital photographs of U before and after leaching. c,d,Digital photographs of LCU before and after leaching. U alone disappeared after being leached, while LCU was transformed from powder to flocs caused by the hydraulicsperturbation of water, thus the spatial scale of LCU increased, making it easily retained by sand (or soil).

Supplementary figure 4. SSNMR spectra of LCU system. a-l, SSNMR spectrum of ATP (pH7), P (pH7), U (pH7), ATP-U (pH7), ATP-P (pH7), P-U (pH7), ATP-P-U (pH1), ATP-P-U (pH3), ATP-P-U (pH5), ATP-P-U (pH7), ATP-P-U (pH9) and ATP-P-U (pH12) respectively. For U at pH7 (c), there were two peaks. Therein, the left peak was probably attributed to the urea molecules (75%) with intermolecular hydrogen bonds (H-bonds) while the right one to those (25%) without H-bond. For ATP-U at pH7 (d), the percent of urea molecules without H-bond was just 6%, which was because of the formation of H-bonds between ATP and the urea molecules without intermolecular H-bonds. For ATP-P-U (pH1), the percent of urea molecules with H-bond was rather low (30%), while that without H-bond was obviously high (63%), indicating that most of the intermolecular hydrogen bonds were broken resulting in more urea molecules without H-bonds. This was because high concentration of H+ was unfavorable for the formation of H-bond. With the increase of pH (from 1 to 12), the percent of U molecules with H-bonds increased, while that without H-bond decreased gradually, presenting that more H-bonds between U and ATP or P formed at higher pH. Additionally, the low amount of P (2‰) in LCU system resulted in the low amount of H-bonds between P and U or ATP compared with those between U and ATP. This result indicated that H-bonds of LCU system were closely related to the composition and pH.

Supplementary figure 5. X-ray diffraction analysis of LCU system. A-E, ATP, U, P, ATP-U and LCU. a-f, pH of 1, 3, 5, 7, 9, 12. The main characteristic peaks (d=3.9718 and 2.8162 nm) of U was intensified with the increase of pH, indicating that the crystallization of urea was improved with pH. It was possibly because the hydrogen bonds number among urea molecules increased causing the increase of the molecules distribution order. As to P, a sharp peak appeared (approximately 10 degree) at pH 9 and 12, which was due to the increase of the structure order related to the hydrogen bonds among the molecules. In addition, being mixed with urea, the fundamental characteristic peak (d=1.03 nm (110)) and Si-O-Si characteristic peaks (20.05 degree (040), 21.06 degree (121)) of ATP did not left shift. This resultprobably indicated that just a few urea molecules accessed the interlayer or the pores of ATP, which was because the pores were too small (3.7×6.3 nm) for urea to access and, nevertheless, relatively available for the access of NH3 withsmaller molecular scale than that of urea.

Supplementary figure 6. Thermal analysis of LCU system. A-C,Thermal gravimetric analysis (TGA)curves of U, U-ATP and LCU respectively. D-F, Differential thermal analysis (DTA) curves of U, U-ATP and LCU respectively. a-f, Under pHconditions of 1, 3, 5, 7, 9, 12. The existence of hydrogen bonds caused the LCU sensitive to pH. At approximately 200 and 330oC, compared with U, the mass loss peaks of U-ATP especially LCU right shifted to higher temperatures. This result demonstrated that ATP could effectively enhance the thermal stability of U. Furthermore, ATP-P could further improve the thermal stability of Uowning to the hydrogen bond effect.

Supplementary figure 7. Comparison of the leaching performance of loss control fertilizer (LCF) with traditional fertilizer in sand column. A, Leaching system. Sample was buried (cylinder shape, diameter of 1.0cm and depth of 2 cm) within the top layer of sand column (25 cm high) which was saturated with water. 100 mL water was sprayed (3mL/min) over the top layer to get 100 mL leachate. Afterwards, the nutrition contents in the leachate were detected. B,NH4+leaching performance of loss control NH4Cl (LCN) (1.0 g, the bottom line) and NH4Cl (0.9 g, the top line). C, HPO4- leaching performance of loss control (NH4)2HPO4 (1.0 g, with 10% loss control agent (LCA), the bottom line) and (NH4)2HPO4 (0.9 g, the top line). D,Urea leaching performance of 1.0 g loss control compound fertilizer (urea:(NH4)2HPO4:KCl=3:1:1, with 10% loss control agent, the bottom line) and 0.9 g compound fertilizer (urea:(NH4)2HPO4:KCl=3:1:1, the top line). Compared with the corresponding traditional fertilizer, the nutrition leaching loss of LCN, loss control (NH4)2HPO4 and loss control compound fertilizer decreased 55.4%, 74.84% and 78% respectively. These results indicated that this technology could effectively control the leaching loss of NH4+, HPO4- and urea in sand.

Supplementary figure 8. Comparison of the leaching performance of LCF (LCN and LCU) with traditional fertilizer (NH4Cl and urea) in soil column. A, Leaching system. Sample(2 g LCN, 2 g LCU, 1.8 g NH4Cl or 1.8 g urea) evenly distributed within the top layer (20 cm deep) of the soil column which was saturated with water. 400 mL water was sprayed (10mL/min) over the top layer every 24 h. After 30 days, the leached N in the leachate and the residue N in the soil column were detected. B,Total leaching loss percent and residue percent in the soil column of N. Compared with the corresponding traditional fertilizer, the N leaching loss of both LCN and LCU obviously decreased and thus the residue N increased. These results indicated that this technology could effectively control the leaching loss of N in soil.

Supplementary figure 9. Comparison of the leaching performance of LCF (LCN and LCU) with traditional fertilizer (NH4Cl and urea) in soil pool. A, Leaching system. Sample (200 g LCN, 200 g LCU, 180 g NH4Cl or 180 g urea) evenly distributed within the top layer (20 cm deep) of the soil pool which was saturated with water. 20 L water was sprayed (10 mL/min) over the top layer every 24 h. After 30 days, the leached N in the leachate was detected. B,Total leaching loss percent of N. Compared with the corresponding traditional fertilizer, the N leaching loss of both LCN and LCU obviously decreased, indicating that this technology could effectively control the leaching loss of N in soil pool.

Supplementary figure 10. Comparison of the NH3 volatilization performance of LCF (LCN and LCU) with traditional fertilizer (NH4Cl and urea) from soil pool. A, Soil pool. Sample (200 g LCN, 200 g LCU, 180 g NH4Cl or 180 g urea) evenly distributed within the top layer (20 cm deep) of the soil pool whosehumiditywas kept 20% under temperatures of 45, 40, 30 and 20oC. The NH3 amount in the greenhouse was detected through Na’s colorimetric method and then the air was refreshed every 24 h for 30 days toobtain the total volatilized NH3 amount. B,Total volatilized NH3 percent. Compared with the corresponding traditional fertilizers, the NH3volatilization loss of both LCN and LCU under these four temperatures obviously decreased, demonstrating that this technology could effectively control the volatilization loss of N from soil pool.

Supplementary figure 11. Agricultural effect of LCF. A(a-e),Rice (Wandao 2009002) field tests of LCF in five counties (Feidong (organic soil), Feixi (sandy loam soil), Juchao (sand soil), Tongcheng(Clay loam soil) and Guangde (loam soil)) of Anhui province. Four fertilizer samples (loss control compound fertilizer (N-P2O5-K2O,19-11-8) (black), compound fertilizer (N-P2O5-K2O,19-11-8) (red), LCU (blue), U (green)) and the control (white) wasrespectively spread with the equal N amount (15 kg/acre, base fertilizer/additional fertilizer =7:3) in 5 acres farmland for each, which wasseparated from the control by plastic in depth of 30 cm. The acre yield of loss control compound fertilizer increased 14% compared with the compound fertilizer, the agricultural effect of which was better than LCU (4% higher than that of urea). B,The mean acre yields of four kinds of crops fertilized by LCF and traditional fertilizer from 2006 to 2009 (50 acres for each, with the equal N amount of 15 kg/acre, base fertilizer/additional fertilizer =7:3). B(a), Rice (Wandao 2009002) with loss control compound fertilizer (N-P2O5-K2O,19-11-8) (gray) and compound fertilizer (N-P2O5-K2O,19-11-8)(black). B(b),Rice (Wandao 2009002) with LCU (gray) and urea (black). B(c),Corn (Zhengdan 958) with LCU (gray) and urea (black). B(d), Wheat (Yumai 66) with loss control compound fertilizer (N-P2O5-K2O,19-11-8) (gray) and compound fertilizer (N-P2O5-K2O,19-11-8) (black). B(e), Cotton (Jimian 516) with loss control compound fertilizer (N-P2O5-K2O,19-11-8) (gray) and compound fertilizer (N-P2O5-K2O,19-11-8) (black). The three-year mean yields of rice, corn and wheat with LCF were higher (approximately 10%) than those with traditional fertilizer, and the cotton yield with LCF was approximately 4% higher than that with traditional fertilizer. The result indicated that LCF could effectively increase the yield of the four kinds of main crops (rice, corn, wheat and cotton). In other words, LCF showed obvious agricultural effects.

Supplementary figure 12. Residue N of LCF in the soil after harvest. Four fertilizer samples (loss control compound fertilizer (N-P2O5-K2O,19-11-8) (black), compound fertilizer (N-P2O5-K2O,19-11-8) (red), LCU (blue), urea (green) ) and the control (white) was respectively spread with the equal N amount (15 kg/acre, base fertilizer/additional fertilizer=7:3) in 5 acres rice (Wandao 2009002) farmland (sand soil) for each which was separated from the control by plastic in depth of 30 cm. The residue N of loss control compound fertilizer and LCU increased 8.8% and 13.0% respectively, compared with compound fertilizer and urea. The result indicated that loss control technology was able to retain N in soil and thus could be continually used by the next crop.

Supplementary figure 13. Modification effect of LCU system on the cation exchange capacity (CEC) of soil. a,ATP. b, Soil (150-250 mesh). c, LCA. d, Soil with 10% (W/W) LCA. e, Soil with 10% (W/W) ATP. f, Soil with 1% (W/W) P. g,Soil with 10% (W/W) U. h,Soil with 10% (W/W) LCU. The CEC was detected through BaSO4 method. Due to the plenty of exchangeableAl3+ and Mg2+, ATP owned a high CEC (404 cmol/kg), meanwhile the CEC of LCA was lower (380 cmol/kg). The addition of 10% LCA could significantly increase the CEC of soil from 12.5 to 37.5 cmol/kg. The modification effect of LCA was better than that of LCU (23.7 cmol/kg) while worse than that of ATP(57.5 cmol/kg). In all, LCU and its components could increase the soil CEC to different degree. The modification ability order (high to low) was ATP, LCA, P, LCU and U. This result illustrated that LCU system was beneficial for the improvement of the nutrition retaining ability of soil.

Supplementary Videos:

Supplementary video 1.This movie shows the 3D structure of ATP alone through X-ray imaging on synchrotron radiation.ATPalone exists as numerous independent aggregates without any network structure (MOV, 272kB).

Supplementary video 2.This movie shows the 3D structure of ATP within LCU through X-ray imaging on synchrotron radiation.Compared with ATP alone(Video S1), ATP within LCU illustrates a high dispersion and few aggregates could be found.More importantly, these ATP rodstransform into 3D networks through connection with each other (MOV, 206kB).

SupplementaryDiscussion:

Supplementary discussion 1. The FTIR spectra of LCU system were shown inFig. 5 in the main text, for ATP-P, the stretching vibration of -NH2 of P was weakened and red shifted from 3450 cm- to 3446 cm-, C-C stretching vibration was weakened and blue shifted from 1634 cm- to 1636 cm-, C-N stretching vibration was weakened and red shifted from 1120 cm- to 1114 cm-. For ATP, the stretching vibrationof coordinated waterwas red shifted from 3546 cm- to 3545 cm-, adsorption water was blue shifted from 3408 cm- to 3420 cm-, -OH swing vibration was red shifted from 640 cm- to 638 cm-, Si-O-Si antisymmetrystretching vibration(1196 cm-) was weakened and red shifted to 1191 cm-, another was intensified and red shifted from 1029 cm- to 1026 cm-, Si-O bend vibration was weakened and red shifted from 580 cm- to 576 cm-. These results demonstrated that hydrogen bonds existed between P (-CONH2) and ATP (coordinated water, adsorption water, -OH and Si-O-Si).

For ATP-U, several information changes could be found. As to urea, N-H stretching vibration was blue shifted from 3447 cm- to 3444 cm-,NH2bend vibration was blue shifted from 1671 cm- to 1681 cm-, which were the typical characteristics of hydrogen bond formation between ATP and urea. Furthermore, after being mixed with urea,stretching vibration (3694 cm-) of the -OH on the surface of ATP was intensified. Moreover, the adsorption water stretching vibration was intensified as well and blue shifted from 3417 cm- to 3435 cm-. As could be deduced from these results, hydrogen bonds existed between ATP (-OH and adsorption water) and U. This was because hydrogen bonds formation could equalize the electron density and decrease the energy of the system, resulting in the strengthened and widened band of -OH stretching vibration.

ForU-P, the N-H stretching vibration (3447 cm-) of urea was red shifted to 3443 cm-, whereas, the NH2bend vibration (1671 cm-) of urea was blue shifted to 1678 cm-, whichproved the existence of hydrogen bonds between U and P.

The FTIR peaks in LCU system partly varied with pH, which also confirmed the existence of hydrogen bonds among U, P and ATP. With the increase of pH, the adsorption waterstretching vibration (3422 cm-) and the bend vibrationof coordinated water (1630 cm-)of ATPwere weakened. Meanwhile, the swing vibration of OH (647 cm-) was weakened when pH was below 9 whileintensified thereafter. Additionally, the translational vibration of OH (434 cm-) was weakened and even disappeared. With pH increase, both NH2 (3342 cm-) and CO (1675 cm-) stretching vibrations of Pwere weakened. For U, NH2 deformation (1604 cm-) and -NCO bend (572 cm-) vibrations became weak with pH increase, while the opposite was observed for C-N stretching vibrations (1032 cm-).In addition, OCNN torsional vibration was weakened and blue shifted from 784 cm- to 787 cm-.

SupplementaryTable:

Supplementary table 1. Brief remarks of all the samples prepared or examined.

Samples / Brief remarks
P / polyacrylamide
U / urea
ATP / attapulgite
LCA / loss control agent (ATP:P =50:1)
LCF / loss control fertilizer (fertilizer:LCA=9:1)
LCU / loss control urea (U:LCA=9:1)
LCN / loss control NH4Cl (NH4Cl:LCA=9:1)

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