In this paper, the carbon footprint of value-added diammonium phosphate containing humic acid (DAPH) were analyzed, calculated, and evaluated in order to provide a scientific basis and theoretical support for the study on the carbon footprint of value-added fertilizers.

The industrial production process of product (from "cradle" to "gate") was defined as the production cycle of product in this study, and the carbon footprint of diammonium phosphate (DAP) and DAPH products was calculated and evaluated referring to the life cycle assessment and PAS 2050 standard.

(1) In terms of phosphorus nutrients (P₂O₅), the carbon footprint of DAP and DAPH production cycle was 3 636.73 kg CO₂-eq·t^-1 P₂O₅ and 3 653.16 kg CO₂-eq·t^-1 P₂O₅, respectively. The carbon footprint (in terms of P₂O₅) of DAPH was only increased by 0.45% compared with DAP. In terms of physical quantity (1 t fertilizer product), the carbon footprint of DAP and DAPH production cycle was 1 672.90 kg CO₂-eq·t^-1 and 1 660.38 kg CO₂-eq·t^-1, respectively, and the carbon footprint of DAPH (in terms of physical quantity) decreased by 0.75% compared with that of DAP. The difference of carbon footprint between DAP and DAPH was attributed to the addition amounts of humic acid synergist (HAS). (2) The carbon footprint of synthetic ammonia accounted for 67.87% and 67.57% of the carbon footprint of DAP and DAPH production cycle, respectively, which was the largest contributor for the carbon footprint of DAP and DAPH during the production cycle. However, the carbon footprint increased by adding HAS only accounted for 0.45% of the carbon footprint of DAPH.

Adding HAS had little effect on the carbon emissions during the DAP production, while synthetic ammonia was the biggest factor affecting the carbon footprint of DAP production cycle.

The application of humic acid enhanced urea (HAU) can effectively reduce ammonia volatilization, and the humic acid in HAU, named UHA, plays a great role in this process. However, due to the reaction between humic acid and urea, the effect of UHA combined with urea on soil ammonia volatilization may be different from that of conventional humic acid (HA). Therefore, the relevant research will help to further reveal the mechanism of HAU reducing ammonia volatilization from soil.

In this study, UHA was extracted by absolute ethanol from HAU. Through indoor constant temperature soil incubation, the effects of HA or UHA combined with urea on soil ammonia volatilization from long-term unfertilized soil or fertilized soil were studied. The dosage of HA or UHA was 0.5% and 5% of the amount of urea, code named 0.5HA+U, 5HA+U, 0.5UHA+U, and 5UHA+U, respectively. At the same time, the treatments with urea (U) and without humic acid and urea (CK) were conducted. Soil ammonia fluxes and volatilization, soil urea-N, nitrate, and ammonium content, and soil urease activity were measured simultaneously.

(1) The ammonia volatilization from long-term fertilized soil for nitrogen fertilization treatments was higher than that from long-term unfertilized soil, which might be related to the decrease of soil pH, the weakening of soil nitrification process and the accumulation of ammonium nitrogen from urea hydrolysis caused by long-term fertilization. (2) Both HA and UHA combined with urea could effectively reduce soil ammonia volatilization, compared with U treatment, but the extent of the reduction depended on whether the soil was fertilized for a long time and the amounts of HA or UHA: urea combined with HA could significantly reduce soil ammonia volatilization for long-term unfertilized soil (P<0.05), and the ammonia volatilization of 0.5HA+U and 5HA+U was 4.4% and 22.9% lower than that under U treatment, respectively. However, the soil ammonia volatilization decreased by only 4.1%–7.5% under the treatment of HA combined with urea, which was not significantly different from that under the treatment of U, when the soil was long-term fertilization. However, urea combined with 0.5%UHA could significantly reduce soil ammonia volatilization (P<0.05) for long-term unfertilized and fertilized soil by 26.5% and 12.9%, respectively. (3) Urea combined with HA or UHA could effectively inhibit urease activity and promote soil nitrification process, respectively, thereby reduced soil ammonia volatilization.

In summary, compared with HA, UHA combined with urea showed better performance on inhibiting ammonia volatilization under soil incubation, and the effect was independent of whether the soil was fertilized for a long time.

Humic acid has complex structure and diverse functions. Studying the direct and indirect effects of humic acid on the growth of maize roots and revealing the regulation mechanism of humic acid on maize roots can provide the theoretical support for further research on the development and application of humic acid fertilizer synergists.

A hydroponic experiment was carried out using Hoagland nutrition solution as the basic cultural liquid and maize cultivar of ‘Zheng Dan 958’ as material with a split-root design. The method of field plot split zone experiment was adopted and eight test treatments was set which was CK-control side (CK-C), CK-control side (CK-C)), HA-non-applied side (HA-C), HA-applied side (HA-T), OHA3-non-applied side (OHA3-C), OHA3-applied side (OHA3-T), OHA6-non-applied side (OHA6-C) and OHA6-applied side (OHA6-T) to study its effects on biomass, root vitality, root morphology and main chemical components of maize different organs.

(1) Single-sided application of humic acid to separate roots significantly increased the fresh root weight of maize on the applied and unapplied sides. Compared with the control, the fresh root weight of maize with the applied side was increased by 21.9%-78.6%, which with the unapplied side was increased by 27.9%-49.3%. (2) The addition of humic acid significantly increased the maize root activity and the total TTC reduction of maize on the applied side and the non-applied side. Compared with the control, the maize root activity and total root TTC reduction of the OHA6-applied side increased the most, which increased by 76.9% and 216.9%, respectively. Compared with the control, HA-applied side and OHA3-applied side treatments increased the maize root activity by 59.8% and 35.1%, respectively. Compared with the control, OHA6-non-applied side, HA-non-applied side and OHA3-non-applied side treatments increased the maize root activity by 62.2%, 53.6% and 25.5%, respectively. (3) Adding humic acid treatment significantly increased the root volume, root surface area, average root diameter, root length and root number on the non-applied and applied sides of maize. (4) Single root application of humic acid could effectively increase the content of maize root ester compounds, protein, amino acids, nucleic acid cellulose and polysaccharides. The application side of humic acid treatment was more conducive to maize root carbohydrates than the non-application side. However, the untreated side under humic acid treatment was more conducive to the accumulation of maize root nucleic acid. The carbohydrate content of the aboveground parts of maize treated with humic acid was significantly higher than that under the blank treatment.

Regardless of whether it was HA or OHA3 and OHA6, when humic acid was applied to separate roots on one side, the growth and activity of maize roots on the side where humic acid was applied were significantly higher than those on the side without humic acid, indicating that humic acid had a direct effect on root regulation. The root growth of the whole plant treated with humic acid on one side was better than that under the control treatment without humic acid on both sides, indicating that humic acid also had an indirect effect in regulating root growth. The root growth of the whole plant treated with humic acid on one side was better than that under the control treatment without humic acid on both sides, indicating that humic acid also had an indirect effect in regulating root growth.

The nitrogen (N) fractions and release characteristics varied much among different types of organic manure. Study and estimation on N fertilizer replacement value of different livestock manures with chemical N as a reference could provide a theoretical basis for rational application of organic fertilizer and scientific combination application of organic and inorganic fertilizers.

In this study, composted pig manure, chicken manure, cattle manure and chemical fertilizer were selected as the research materials. There were six application rates of N set, i.e. 0, 40, 80, 120, 160 and 200 mg·kg^-1 dry soil, respectively. A soil column experiment was conducted to investigate the effects of N derived from manure and chemical fertilizers on wheat yield and N uptake. Furthermore, the relative replacement equivalence of N in three kinds of manure was calculated by using the response between crop N uptake or yield and N application rate.

(1) The grain yield and biomass of wheat were increased with the elevated N application rate. When 40-120 mg·kg^-1 dry soil input, the increase of grain and biological yield of chemical fertilizer and pig manure was higher than that of chicken manure and cow manure, while there was no significant difference among grain yield treated with chemical fertilizer, pig manure and chicken manure, except being significantly higher than the cow manure, when N input at 160-200 mg·kg^-1. (2) At the same N input rate, chemical fertilizer could significantly improve wheat grain N uptake and aboveground N uptake compared with manure treatment. For three kinds of manure treatment, the total aboveground N uptake associated with pig manure was the highest, that with chicken manure followed, and that with cow manure was the low. In this study, the N recovery rate under three kinds of manure treatments was firstly increased and then decreased with the elevated N application level, while the N recovery rate of chemical fertilizer showed a gradually decrease trend. (3) When N input at different application levels, the relative N replacement value of pig manure, chicken manure, and cow manure were 37.7%-84.2%, 23.1%-71.0% and 11.3%-34.2%, respectively, with wheat grain yield as a reference index; 49.2%-91.3%, 23.3%-78.3%, 7.4%-42.2% with aboveground biomass as a reference index; 31.1%-76.3%, 19.8%-67.1%, 6.0%-35.7% with grain N uptake as a reference index; 30.8%-97.1%, 19.8%-75.6%, 7.8%-43.8% with aboveground N uptake as a reference index. There was a positive correlation (P<0.01) between the N replacement value of organic manure and N application rate.

In this study, the relative N replacement value of organic manure was affected by both organic fertilizer types and N application rate. Within a certain range of N application level, the N replacement value of livestock manure increased with the increase of N application level. The average relative equivalent of N replacement by pig manure, chicken manure, and cow manure were 59.6%, 46.2%, and 23.6%, respectively.