Biochar has been used as an input in the animal farming industry since 2010 (Gerlach and Schmidt, 2012; Schmidt et al., 2019). Several studies have documented the positive effects of biochar, used as a feed supplement, on both live-stock and soil health. Schmidt et al. (2019) examined 112 studies, in which the addition of a small amount of biochar to fodder improved the animal immune system, digestibility, and quality of milk and meat, while eliminating toxins.Gerlach and Schmidt (2012) conducted a survey, in which biochar was fed to 150 cattle, and found that both the milk protein and fat increased when biochar was added to silage. Erickson et al. (2011) investigated the effect of activated biochar, fed to Holstein dairy cows at 0, 20, and 40 g daily, on fungal-contaminated feed silage. Compared to the control, biochar considerably improved feed intake and digestibility, and increased milk fat.
The application of animal manure mixed with porou biochar into soil also offers multiple agronomic and economic benefits by providing plants with essential nutrient and reducing nutrient release from the soil. Joseph et al. (2015b) studied the effect of a Jarrah wood biochar, mixed with molasses and fed to cows, on soil (Chromosol) properties. The manure-biochar mixture significantly improved the soil properties by capturing organic compounds and mineral nutrients that would otherwise be leached. While numerous studies have focused on changes in either livestock productivity or soil health as a result of biochar being fed to dairy cows, a systematic study that investigates changes in a whole farming system following the addition of biochar to fodder has not been undertaken.
A 9-month study was conducted on a dairy farm with 250 cows (in 2019) in South Australia (SA), while prior studies were undertaken in Western Australia (Joseph et al., 2015b, 2020). The cows received biochar through a feed supplement for over 9 months. The changes in milk yield and quality, soil and plant minerals, and manure characteristics were investigated over 9 months. Historical milk quality and yield data from 2017 and 2018 were used to determine if there were significant changes in the milk yield and quality in 2019. The farmers’ income was also assessed. The results of this study will elucidate how biochar may benefit farming systems, especially in dry and hot years.
Biochar was provided by Mara Seeds Pty Ltd., Australia. The biochar was produced from a mixture of 50.0% eucalyp- tus wood chips, 25.0% soybean residue, and 25.0% tea tree mulch at a pyrolysis temperature of 350–500 ◦C. A 9-month feeding trial was started in January 2019 on a dairy farm with 250 Jersey milking cows in the Fleurieu Peninsula, SA. The biochar was mixed with a feed supplement at a rate of 0.006% of total dry matter (DM). The feed supplement also included triticale, wheat, lupin, mineral pellets, and canola oil. The supplement (18.0% crude protein and 13.6% metabolizable energy) provided 15.0% of the total intake of the cows. Seventy percent of the intake (28.0% of DM as crude protein and 12.9% of DM as metabolizable energy) came from ryegrass and clover on pastures. The remaining 15.0%, which contained 10.0% of DM as crude protein and 7.7% as metabolizable energy, was from fodder. The five animals selected for the study consumed 25 kg of DM intake per day. The biochar, combined with the feed supplement, was fed to the cows for 9 months. The same feeding regime as used in 2017 and 2018 was applied in 2019 to determine if there were significant changes in yield. The data set included 5 308 measurements on 509 cows across 22 testing days (every 6 weeks). Milk yield (19.3 L head−1 d −1), protein, and fat were measured by the National Herd Co-Operative in Australia, using the methods specified in the Australian New Zealand Food Standards Code (Standard 2.5.1).
Approximately 10 t ha−1 of biochar-infused manure was spread across 200 ha by 250 cows in a year (250 cows produce about 1 t of manure (DM) per day). There was an abundance of both summer- and winter-active dung beetles to incorporate the biochar-infused manure, and irrigation was used across the farm. It should be noted that Australia experienced three continuous hot years from 2017 to 2019, among which 2019 was the hottest, as reported by the Bureau of Meteorology, Executive Agency of the Australian Government (2020) (Fig. S1, see Supplementary Material for Fig. S1). Hence, data from 2019 were compared to the two similar years. Before biochar feeding began in January 2019, 15 soil and plant samples were collected across a 30-m transect in a 3.5-ha paddock. The paddock was irrigated and strip-grazed (for 3 d) five times during the growing season. During the 9-month period, about 75 t of manure (wet weight) was deposited onto the soil through cow excretion, along with a total of 1 825 t administered across the entire farm.
The total amount of biochar excreted across the farm was approximately 10 t. Soil, pasture, and plant tissue samples were collected in January (before the biochar was fed) and September (after biochar was fed) and subsequently analyzed. Samples from the same animals were collected in both January and September, dried at 50 ◦C for 5 h, and stored at 4 ◦C.
Semi-quantitative determination of elements and heavy metal concentrations in the samples was performed using laser ablation inductively coupled plasma mass spectrometry (PerkinElmer, Shelton, USA). The ultimate analysis was performed using a vario MACRO cube combustion analyzer Elementar, Langenselbold, Germany). Both the pH and electrical conductivity (EC) values of the biochar, as well as the pH and oxidation-reduction potential values of the manure samples were measured. The microstructure and distribution of organic and inorganic compounds within the biochar were analyzed using scanning electron microscopy (SEM) together with an x-ray energy dispersive spectrometry detector. X-ray photoelectron spectroscopy (XPS) was used to examine the surface functional groups. Details on both instruments were explained in Taherymoosavi et al. (2018).
Total dissolved C and N were measured using Multi N/C 3100 analyzer (Analytik Jena, Thuringia, Germany). To study the changes in dissolved organic carbon (DOC), a DOC-labor liquid chromatography-organic carbon detection was applied as described in Taherymoosavi et al. (2016). A Quadrupole Nexion inductively coupled plasma mass spectrometer (PerkinElmer, Shelton, USA) was used to determine the concentrations of soluble elements. Soil and plant analyses were conducted at the Australian Precision Ag Laboratory. Milk yield on a farm depends on many factors, including the age of cows, milking period, supplementary feed, quality of the pasture, and environmental factors. Thus, it is difficult to establish a control group for working farms in commercial dairies. In this study, the “control” treatment was a function of time (samples collected in January). A linear mixed effect regression (LMER) model was applied to determine the possible changes in milk quantity and quality (Bates et al., 2015; Butler et al., 2018). The first method (model 1) investigated gross changes over the three years, whereas the second method (model 2) considered the complex factors related to age and lactation.
Details are provided in the Supplementary Material. Initial characterization of the biochar (Table SI, see Supplementary Material for Table SI) showed that the biochar was almost neutral with pH and EC values of 7.3 and 2.7mS cm−1, respectively. The biochar had significantly higher Ca, Al, Fe, P, Mg, and Na concentrations, but lower P and S concentrations than the Jarrah biochar, produced at 600 ◦C, fed to cows in another study (Joseph et al., 2015b). The biochar also contained a lower C concentration (61.45%, weight percent), but a higher N concentration (0.7%, weight percent) than those reported for the Jarrah biochar (82.0% and 0.4%, respectively) because of the lower production temperature. The heavy metal levels (Table SI) were below the upper limits specified by the United States Environmental Protection Agency (US EPA) standard (International Bio-char Initiative, 2015). Microscopic analysis of the biochar (Fig. S2, see Supplementary Material for Fig. S2) revealed mineral particles inside the biochar pores that reacted with the biochar (point a). Cr is formed from the conductive coating. There was also evidence of the formation of C/Si/O clusters on the surface of the biochar (point b, Fig. S2b), possibly formed during the pyrolysis. Silicon is considered as an essential element for increasing soil resistance to high levels of toxic metals, increasing soil exchange capacity, and improving the availability of P to plants (Greger et al., 2018). The evaluation of the effect of biochar on milk yield (Fig. S3, see Supplementary Material for Fig. S3) indicated an initial drop in January 2019. The milk yield increased for all the 2- and 3-year-old animals after 1 month. Particularly in these cows, an upward trend, greater than that in previous years, was observed in winter (June to August). The milk yield decreased to a lower level than that in previous years for the 3- and 4-year-old and mature cows once biochar feeding ceased. This was presumably due to the sudden discontinuation of supplements, as noted in other dairy farms.
A preliminary analysis (model 1; Table SII, see SupplementaryMaterial for Table SII) indicated an increase in the average milk yield by 1.4 ± 0.44 L head−1 d−1 (8.2% in a volume ratio) during the 9 months of biochar feeding compared to that in the previous 2 years (when no biochar was included in the feed). Biochar may contribute to the abundance of beneficial bacteria in the rumen (O’Toole et al., 2016), which may contribute to improved feed digestibility and intake efficiency (Schmidt et al., 2019). There were decreases in fat (0.6%) and protein (0.24%), while no significant change was observed in the total quantity of either fat or protein in kg head−1 d−1 (%fat is the ratio of fat to milk yield expressed as a percentage) when compared to previous years.
Changes in the fat and protein were also influenced by the age of the cows (Table SIII, see Supplementary Material for Table SIII). A subsequent analysis (model 2; Table SIV, see Supplementary Material for Table SIV), which included an additional herd test and lactation data, showed an increase of 0.4 L head−1 d−1 in milk yield (2.2%, P > 0.05), but none of the traits analyzed were significantly affected by the addition of biochar.
Characterization of the manure products showed an increase in pH from 7.1 to 7.3 within 9 months, which was negatively correlated with Eh value (Fig. S4, see Supplementary Material for Fig. S4). The Eh value (Ag/AgCl) reduced from −96 to −268 mV at the end of the trial. This can further affect soil Eh and, thus, the availability of soil and plant nutrients (such as P and N), as noted by Joseph et al. (2015a). The concentrations of N and C in the manure samples (Fig. 1) increased by 0.78% and 2.17% (P < 0.05), respectively, within 9 months. The C/N ratio for the manure samples was higher than that reported for cattle manure (10.7) in the literature (Huang et al., 2017). The C/N ratio in the manure was 17.6 in January and reduced to 13.8 in September. This may indicate the ability of biochar to retain N, which could further influence soil N and the microbial community once it is applied to the soil (Almeida et al.,2019).
The concentrations of the other elements in the manure samples are shown in Fig. 2. The concentrations of Na, Al, P, S, K, Ca, and Fe were higher in the manure samples collected in September, while the concentration of Mg was lower. Analysis of variance (ANOVA) (Table SV, see Supplementary Material for Table SV) showed a significant difference in the concentrations of K, S, Ca, and Fe between the samples collected in January and September, while significantly greater concentrations of K (3 886.66 mg kg−1), S (1 491.0 mg kg−1), Ca (46 216.7 mg kg−1), and Fe (1 617.86 mg kg−1) were found in the manure samples taken in September (P < 0.05). The heavy metal concentrations in the manure samples (Table SVI, see Supplementary Material for Table SVI) were below the upper limit values reported in New South Wales (NSW), Australia, for soil conditioners.
(Dorahy et al., 2007; Salo et al., 2018). Thus, the manure samples are environmentally safe for soil applications. Understanding the changes in the surface functionalities of manure is important because it determines how its constituents interact with soil components when applied as an amendment (Joseph et al., 2015b). As can be seen in Table I, the biochar had a lower surface C–C/C–H/C=C, but a higher organic C concentration, associated with alcoholic, phenolic, and hydroxyl groups, than did the Jarrah biochar (Joseph et al., 2015b). Two classes ofNfunctionalities, N–C– COOH/pyridone and NH2/amino type N, were found on the surface of the biochar. The biochar contained higher surface N, Ca, P, Na, and Mg concentrations than those reported in the literature for the wheat straw and Jarrah biochars (Joseph et al., 2015b; Taherymoosavi et al., 2018). A comparison between the manure samples showed a higher proportion of total surface C functional groups in January (79.49 atomic
percent (at.%)), which reduced to 74.44 at.% at the end of the experiment. C functionalities, mainly C–C/C–H/C=C, may have decomposed to form new bonds with the biochar components. The principal C functional groups were aromatic C and aliphatic structures (C–C/C–H/C=C). The relative proportion of this bond reduced by 5.05 at.%, whereas the relative proportion of oxygen-containing functionalities, C–O, C=O and carboxylic groups, increased by 2.57 at.% after 9 months. These functional groups are responsible for increasing nutrient availability and locking up heavy metals (Joseph et al., 2018).
A greater total N species content was detected on the surface of the manure samples taken in September (3.27 at.%). The predominant N functional group was NH2/amino type N, which increased from 2.69 at.% in January to 2.93 at.% in September. A new chemisorbed NH4 was detected in the manure samples collected in September (0.34 at.%), implying that the biochar was effective in bonding with some of the ammonium ions (Joseph et al., 2018). Higher concentrations of Ca (0.91 at.%), P (0.65 at.%), Mg (0.52 at.%), and Si (0.38 at.%) were also found on the surface of the manure in September. A higher P concentration on the surface of the manure in September was possibly absorbed by the soil and plant tissues; this is supported by the results of the soil and plant analyses mentioned below.
Examination of the total dissolved C (TDC) and N (TDN), shown in Fig. 3, implied a significant difference in TDC concentration between the manures in the two seasons (P <0.05, Table SVII, see Supplementary Material for Table SVII). The concentrations of both TDC and TDN increased by 1 179 and 97 mg L−1, respectively, in September, but the change in TDN was not significant (P > 0.05, Table SVII). However, compared to the N and C originally present in the manure (Fig. 1), relatively lower and higher proportions of N and C, respectively, were released from the manure in September (Fig. 3). A lower total C but higher total N on the surface of the manure in September was also supported by XPS analysis (Table I), suggesting the ability of the biochar to store N in the manure.
Dissolved organic carbon is one of the sources of soil organic matter for improving soil fertility and increasing plant growth (Silveira, 2005). Quantitative analysis of the DOC and its fractions, shown in Table II, indicated that the manure collected in January had a higher DOC concentration (71.6 mg g−1) than that collected in September (58.5 mg g−1). The biochar in the manure could contribute to binding with organic C, which is not water-soluble. This could result in an increase in long-term soil C when biochar-infused manure is applied. The largest hydrophilic DOC fraction was that of humic-like substances. The relative proportion of these molecules decreased from 30.03% in January to 21.2% in September. Conversely, the relative proportion of low-molecular-weight (LMW) acids increased from 9.1% to 16.0% over the 9 months. This indicates that the biochar assisted in breaking down the organic fractions into low weight organic molecules, such as acetic, malic, citric, lactic, and carbolic acids, which can facilitate the availability of nutrients (Reynolds et al., 2018; Schmidt et al., 2019).
Feeding the biochar to cows also reduced the concentration of DON bonded with humic-like substances from 2.32 to 0.7 mg g−1 and the N/C ratio from 0.11 to 0.06. This is in good agreement with the XPS and elemental analyses (Fig. 1), where the manure had a lower N/C ratio (0.057) in January than in September (0.073), indicating the capability of the biochar to retain N. Figure 4 compares the concentrations of the other elements dissolved from manure. A comparison between the two manures showed significantly lower amounts of Na, Fe, and S released from the manure in September (P < 0.05, Table SVIII, see Supplementary Material for Table SVIII). The concentrations of dissolved Ca, K, Mg, and Si reduced after 9 months, but the changes were not significant (P > 0.05, Table SVIII). A comparison between the concentration of mineral elements presents in the manure samples (Fig. 2) and the concentration of dissolved elements released from the manure samples (Fig. 4) revealed lower proportions of Na (3.6%), K (10.3%), Si (0.14%), Ca (0.52%), and Fe (0.21%), but higher proportions of Mg (5.9%) and P (2.7%), released from the manure collected in September. Further investigations are required to understand whether these reductions are affected by environmental parameters and climate change.
The properties of the soil, collected at the depth of 0–20 cm (Table III), showed an increase in pH by 0.47 in September, which was consistent with the manure analysis (Fig. S4). The EC, a measurement of total salt content, increased by 0.01 dS m−1, indicating that the total ions were slightly increased in the soil during the experiment. The effective cation exchange capacity (ECEC), an indication of soil capacity to retain mineral nutrients, also increased by 0.04 cmol kg−1, which resulted in an increase in the concentrations of soil available P, Ca, K, and Mn. A comparison between the available P in the soil (Table III) and in the manure (Fig. 2) revealed that the ratio of P (September/ January) increased from 1.09 in the manure to 1.18 in the soil. The increase in soil available P could be due to a greater concentration of P leached from the manure in September (Fig. 4), which was absorbed by the soil. These increases in soil ECEC and available mineral nutrients (noted by Joseph et al., 2015b) suggest that the soil became more fertile within 9 months. The extractable NH+4 -N and NO− 3 -N reduced by 2.7 and 3.2 mg kg−1, respectively, in September; N could be absorbed by the pasture during springtime (Table IV). There were also decreases in soil Mg, S, Na, and Fe in September, which could be due to either the capacity of the biochar to store them or the absorption of these minerals by the plant tissues and pasture.
The analysis of plant tissues (Table IV) showed increases in N, P, K, Fe, and Al over time. The P ratio (September/ January) in the manure (Fig. 2)was 1.09, which increased to 1.46 in the plant tissues (Table IV), indicating a higher concentration of P absorbed by the plant tissues compared to the soil available P (Table III). A lower extractable NH+4 -N and NO+3 -N in the soil in September than in January (Table III) possibly implied that N was taken up by the plant tissues (Table IV). The N ratio (September/January) was 1.34 in the manure (Fig. 1), which increased to 1.57 in plant tissues (Table IV). Increases in NH+4 -N and P availability were also noted by Mia et al. (2019) following the application of wood biochar to Dermosol. Although biochar-infused manure application increased the soil Ca concentration (Table III), the additional Ca was not adsorbed by the plant tissues. Both Mg and Na reduced in soil and plant tissues in September. The application of biochar-infused manure also reduced the concentrations of heavy metals, including Cu, Zn, and B, in plant tissues. Figure S5 (see Supplementary Material for Fig. S5) indicated improvements in the quality of the pasture, including digestibility, metabolizable energy, and crude protein, in September. Both the neutral detergent fiber (NDF) and acid detergent fiber (ADF), used to evaluate forage and feeding value, were lower in September. This suggests that the quality of hay improved; hence, the amount of consumed forage reduced over time (Choi et al., 2020) for the same weight gain, while more milk was produced.
Investigating the financial benefits also revealed that the overall income increased by $22 000 (10.0%), compared to that in the previous year, over 9 months. Of this increase, 1.6% ($3 600) was due to a small increase in the milk price. Based on the range of increase in milk yield, provided by the LMER model, the increase in the farmer’s income would be between 6.0% and 21.0%. Cows also consumed less fodder (about 1 t per week), which could be due to better pasture quality (Fig. S5). The benefit of biochar feeding was greater than the cost of biochar ($6 120 for 9 months).
A systematic 9-month farm study was conducted to examine the changes in milk productivity, manure properties, and soil and plant health following biochar feeding to dairy cows. Analyses showed marginal increases in milk yield (2.2%, P > 0.05) for each cow and farm income (by a minimum of 6.0%). Biochar reduced the release of Na, Ca, Fe, and Si, but increased the release of P and Mg from the manure after 9 months. The soil available P, K, and Ca and plant available N, P, and K improved over time. The pasture quality improved within 9 months; thus, cows consumed less fodder over time. Further investigations are required to examine whether the changes in yield, manure, soil, and plant tissues were influenced by the nature of dairy management, herd structure, and environmental parameters.
