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ISSN : 2287-5824(Print)
ISSN : 2287-5832(Online)
Journal of The Korean Society of Grassland and Forage Science Vol.46 No.1 pp.65-75
DOI : https://doi.org/10.5333/KGFS.2026.46.1.65

Livestock Manure Application and Its Relationship with Forage Crop Productivity and Hanwoo Carrying Capacity per Unit Area: A Narrative Review

Soon Hwangbo
Department of Companion Animal Industry, Daegu University, Gyeongsan 38453, Republic of Korea
*Corresponding author: Soon Hwangbo, Republic of Korea. Tel: +82-53-850-6770, Fax: +82-53-850-6779, E-mail: simona@daegu.ac.kr
February 6, 2026 March 2, 2026 March 4, 2026

Abstract


This study reviewed previous research on livestock manure application in forage crop fields, with a focus on forage productivity, forage quality, and Hanwoo carrying capacity per unit area. This work was conducted as a narrative review, not as a systematic review or meta-analysis. Studies published between 2000 and 2025 were collected from the Research Information Sharing Service (RISS), the Korean Citation Index (KCI), DBpia, and Google Scholar. Many studies reported that manure application increased dry matter yield and improved forage nutritional components such as crude protein and total digestible nutrients. However, the size of these effects differed depending on crop type, soil condition, weather, and application rate. In several cases, nutrient use efficiency was lower under high rainfall or unstable temperature conditions, especially when liquid manure was applied. Carrying capacity was estimated using assumed animal body weight and forage contribution. When different assumptions were applied, the calculated values changed. This shows that carrying capacity is not a fixed number but a relative measure, and the results should not be used directly without considering farm management conditions. Livestock manure application increased forage production and helped nutrient movement in crop–livestock systems. However, similar results cannot be expected in all environments. Future studies should consider soil characteristics, forage productivity, forage use, and livestock performance together.


Carrying capacity , Forage crop , Hanwoo , Livestock manure , Nutrient management

초록

    Ⅰ. INTRODUCTION

    In recent years, feed consumption in the Korean livestock industry has gradually increased along with the expansion of farm size. As livestock farms have shifted from small-scale to large-scale operations, the amount of feed used has increased, and feed cost has become a major issue in livestock management (Chae et al., 2020). Not only concentrate feed but also the total feed cost including forage has increased, and rising feed prices directly affect farm income (Chang, 2018;Sohn et al., 2025).

    In Korea, a large amount of grain used for livestock feed comes from imports. Because of this structure, domestic feed prices are affected by movements in the global grain market (Lee et al., 2024). In the past few years, international grain prices have shown an overall increase. This trend has been associated with lower grain production under climate-related conditions and also with growing bioenergy demand (Tigchelaar et al., 2018). When grain prices increase, feed costs usually rise as well, and livestock farms feel this change in their management (Jeong and Yang, 2022). Under these circumstances, discussions about strengthening domestic feed resources have continued (Kim et al., 2020).

    At the same time, livestock manure production has continuously increased as the number of animals has grown. As a result, manure treatment and management remain recurring issues in the livestock sector (Go and Kim, 2024). If manure is not properly managed, environmental problems such as odor, water pollution, and soil contamination may occur (Cai et al., 2021). In rural areas, complaints related to livestock manure are still common. This has increased interest in both manure treatment and practical ways to use manure (Han and Hong, 2025).

    Recently, there have been more attempts to view livestock manure not simply as waste, but as a resource that can be used in agricultural production. Livestock manure contains essential nutrients for crop growth, including nitrogen, phosphorus, and potassium, so it can be used as a fertilizer resource (Sadeghpour and Keshavarz Afshar, 2024). When manure is used as a nutrient source during forage crop cultivation, it may reduce the use of chemical fertilizers. Some studies also reported improvements in soil organic matter content (Rayne and Aula, 2020;Yoo et al., 2021).

    Gyeongsangbuk-do is one of the regions with a high number of Hanwoo cattle in Korea. Forage demand is also high in this region. However, the local forage production base is not sufficient, and a considerable amount of forage is supplied from other regions (Lee et al., 2022). In this situation, studies have been conducted, mainly in Gyeongsangbuk-do, to analyze the effects of livestock manure application on forage crop productivity and forage value. Some studies also presented the results by converting them into Hanwoo carrying capacity per unit area (Choi, 2021).

    Evaluation of Hanwoo carrying capacity per unit area is used as an indicator to interpret forage production results in relation to livestock farm management (Hwangbo et al., 2015). This indicator can show, in a relatively direct way, how much improved forage productivity may be linked to an increase in the number of cattle that can be supported (Hwangbo and Oh, 2017). However, the results may differ depending on crop species, cultivation region, and fertilization level (Hwangbo and Jo, 2014). For this reason, it is necessary to summarize and organize related findings in an integrated manner.

    Therefore, this study aims to review the effects of livestock manure application on forage crop productivity, forage value, and Hanwoo carrying capacity per unit area. The findings are expected to provide basic information for improving forage selfsufficiency and supporting stable Hanwoo farm management.

    Ⅱ. LITERATURE SEARCH AND SELECTION METHOD

    1. Search strategy

    This study was conducted as a narrative review and did not follow a strict systematic review protocol. The main goal was to bring together studies on forage production using livestock manure in Korea. Studies were included when they contained data that could be applied to estimating crop productivity or Hanwoo carrying capacity per unit area.

    The literature search was conducted using the Research Information Sharing Service (RISS), the Korean Citation Index (KCI), DBpia, and Google Scholar. Studies published between 2000 and 2025 were reviewed. The search terms were adjusted during the process, depending on the database and the scope of the results. They generally included livestock manure, cattle manure, pig manure, slurry, forage crops, dry matter yield, crude protein, total digestible nutrients (TDN), and carrying capacity.

    2. Inclusion scope

    Studies were mainly included if they reported forage productivity indicators such as dry matter yield, or forage quality indicators such as crude protein and TDN. Studies that presented results as carrying capacity per unit area were also included. In contrast, papers were excluded when the link between manure application and forage crop cultivation was weak. Studies with unclear treatment conditions or unclear results were also excluded because they were hard to compare.

    3. Review process

    First, studies were screened using titles and abstracts. After that, full texts were checked when needed. Duplicate records were removed during the review process. In the final step, only studies with available full texts were used for the summary. Studies were excluded when forage yield or quality data were not available, when manure application was unclear, or when full texts could not be accessed. Only studies reporting forage productivity or forage quality after livestock manure application were used in the final analysis.

    4. Data extraction and summary

    From the included studies, crop type, manure form, application level, and experimental conditions were checked. Outcome indicators such as dry matter yield, crude protein, TDN, and carrying capacity per unit area were extracted and summarized.

    Ⅲ. EFFECTS OF LIVESTOCK MANURE APPLICATION ON FORAGE CROP PRODUCTIVITY AND FORAGE VALUE

    Livestock manure contains various inorganic nutrients and organic matter, including nitrogen, phosphorus, and potassium, and it has long been used to support crop growth (Prado et al., 2022). Since manure generated from livestock farms requires cost and labor for treatment, efforts to recycle it for agricultural production have continued (Sefeedpari et al., 2019). Using livestock manure as a fertilizer resource during forage crop cultivation has received attention because it can reduce the use of chemical fertilizers. Related effects have been reported in several previous studies (Annicchiarico et al., 2011;Cho et al., 2013a;Jo et al., 2010).

    1. Changes in productivity (Dry matter yield)

    When manure was applied to forage crops, dry matter yield was higher than in plots without manure in most cases. The size of the increase was not the same for all crops and also varied with the amount applied. Based on the studies listed in Table 1, yield increases were roughly around 70%, and in some situations they were more than twice the control level. Corn and sorghum × sudangrass showed larger increases compared with other crops. Rye and barley did not show large increases, but there was still some positive change.

    Similar responses have been described in oat, wheat, and other gramineous forages (Lim et al., 2003;Shin et al., 1999;Song et al., 2006). This pattern may be linked to the way nutrients are released from manure. Unlike readily soluble fertilizers, livestock manure supplies nitrogen over time. For crops with longer growing periods, this gradual supply could support continued biomass accumulation through the season (Rodd et al., 2021).

    Previous studies on the effects of livestock manure application on forage crop productivity have mainly presented results focusing on changes in dry matter yield and forage value. The main findings of related studies are summarized in Table 1.

    When manure was applied at approximately 100–150 kg N/ha, dry matter yield generally increased without large fluctuations. Most studies reporting this nitrogen range were conducted on winter cereal crops such as whole crop wheat and barley under upland field conditions. Within this range, both crude protein yield and total digestible nutrients (TDN) yield also increased, indicating that the response involved not only greater biomass but also greater total nutrient production (Liimatainen et al., 2022;Hwang et al., 2007).

    In contrast, some studies reported that the increase in productivity was small when manure was applied at low rates. This was probably because the nutrient supply was not enough for normal crop growth (Motsi et al., 2025). At low application levels, yield increases were not very large, and in some cases the differences were not statistically significant. Simply applying manure did not always result in higher productivity. The effect seemed to depend on whether the nutrients supplied were sufficient to meet the crop’s needs (Kim et al., 2009;Lee et al., 2005;Fan et al., 2020).

    2. Changes in forage value

    In terms of forage value, livestock manure application is generally summarized as having positive effects (Miner et al., 2020).

    In most of the reviewed studies, manure application led to a modest rise in crude protein (CP) content. The difference was often around 1–4 percentage points compared with unfertilized plots. When legumes were included in mixed sowing, the increase was more pronounced, and CP levels in some cases were close to double those of the control (Hwangbo et al., 2015). Many studies reported that manure-treated plots tended to have higher crude protein content than non-fertilized plots. This increase is likely associated with the nitrogen supplied from manure, which supports protein formation in plant tissues (Cho et al., 2013b). Several studies also noted that manure application can partly compensate for the decrease in protein content that may occur when gramineous forage crops are continuously grown as a single crop (Thers et al., 2022;Zheng et al., 2025).

    Some studies reported that manure application did not affect fiber content, while TDN was maintained or slightly increased (Lee and Jeon, 2004). Total digestible nutrients (TDN) content generally showed small changes, often remaining stable or increasing by 0–3%, even when dry matter yield increased (Lim et al., 2006). This suggests that manure application can increase productivity without greatly lowering the digestibility of forage (Lim et al., 2006). In many studies, manure application resulted in higher yields compared with plots without manure, and crude protein content was also higher. However, even when yield and crude protein increased, overall forage quality did not change much.

    3. Effects of crop type, soil, and weather conditions

    However, the effects of manure application were shown to vary depending on soil and weather conditions (Hwang, 2007). In areas with higher soil organic matter and fertility, the manure effect tended to be more stable (Ruelle et al., 2022). In contrast, in areas with low soil fertility and insufficient phosphorus, the productivity increase was reported to be smaller (Asai et al., 2025).

    Weather conditions also influence the effects of manure application (Zhu et al., 2022). When rainfall is high or temperature fluctuations during the growing period are large, nutrient use efficiency from manure can be low, and productivity improvement may not be large (Park et al., 2006). This point is important especially when liquid manure is applied, because nitrogen leaching or nutrient loss can occur depending on rainfall conditions (Uusi-Kämppä and Mattila, 2010).

    Overall, livestock manure application can help improve forage crop productivity and forage value. However, the effects can differ depending on application rate, crop type, soil status, and weather conditions. For this reason, it is difficult to expect the same results under all conditions. Livestock manure should be applied at an appropriate level by considering local conditions and cultivation environments.

    4. Differences by manure type and application method

    In several studies, forage yield increased after manure application. Still, the amount of increase was not identical in all cases. It seemed to change with the manure type. The way the manure was applied also made some difference. The related results are shown in Table 2.

    In several trials, slurry application produced a bit more dry matter than compost (Hwangbo et al., 2015). The difference was not very large in most cases, but slurry generally resulted in slightly higher biomass (Choi et al., 2012;Jo et al., 2010). When legumes were included in the mixture, crude protein levels were generally higher (Jo, 2012). This also resulted in higher estimated carrying capacity in those cases.

    Ⅳ. LIVESTOCK MANURE APPLICATION AND EVALUATION OF HANWOO CARRYING CAPACITY PER UNIT AREA

    In studies related to forage crop cultivation, results are often presented mainly using dry matter yield or forage value indicators (Lim et al., 2007). These indicators are useful for evaluating crop productivity and quality. However, they have limitations in directly explaining how many animals can actually be raised under farm conditions (Oh et al., 2014). To address this issue, some previous studies attempted to convert forage crop productivity and forage value into Hanwoo or organic Hanwoo carrying capacity per unit area (Hwangbo and Oh, 2017).

    Evaluation of Hanwoo carrying capacity per unit area deals with estimating how many animals can be supported from a given area. The estimation is based on the dry matter yield and nutrient content of the forage produced (Jo et al., 2008).

    Dry matter yield or crude protein (CP) by itself does not say much about actual feeding capacity. Carrying capacity is linked with total forage production and nutrient supply together, so the value changes depending on those conditions. In forage studies, it has been used mainly as a management reference. The calculation criteria reported in domestic studies are shown in Table 3.

    Annual CP and TDN per hectare were calculated from dry matter yield and nutrient concentration values (Jo, 2012). The yearly nutrient amounts were compared with animal requirements (Hwangbo and Jo, 2013;RDA, 2012). The figures differed slightly among studies. The annual requirement was based on daily intake standards of 426.3 g CP and 3.479 kg TDN, multiplied by 365 days. A body weight of 450 kg and a forage proportion of 70% were assumed for a Hanwoo heifer. Finally, carrying capacity (head/ha/year) was calculated by taking the average of the CP- and TDN-based values (Jo, 2012).

    In previous studies conducted mainly in Gyeongsangbuk-do, carrying capacity was generally calculated based on Hanwoo cattle with a body weight of about 450 kg. The forage feeding ratio was often set at around 70% (Jo, 2012). Using these assumptions, manure-treated plots commonly showed a clear increase in carrying capacity compared with non-fertilized controls. In several summer forage studies, carrying capacity increased from approximately 2.8–3.1 head/ha/year in control plots to 5.6–6.0 head/ha/year under slurry application, representing nearly a two-fold increase (Table 1). These criteria reflect common feeding practices for Hanwoo in Korea. Because of this, it is relatively easy to apply the results to actual farm conditions. Another advantage is that using the same calculation criteria allows comparisons across different studies, which is one characteristic of the carrying capacity indicator (Hwangbo and Jo, 2013).

    When reviewing studies on the effects of livestock manure application, carrying capacity per unit area was higher in manure-treated plots than in non-fertilized plots (Choi et al., 2012). Across studies summarized in Table 1, the increase in carrying capacity generally ranged from 30% to over 100%, depending on crop type and manure rate. Winter forage systems showed moderate increases, whereas summer forage crops such as corn often showed larger gains.

    This increase was linked to higher dry matter yield, crude protein yield, and TDN yield (Choi et al., 2012). Since both biomass and nutrient yield increased simultaneously, the amount of forage available per hectare was sufficient to support more animals under the same feeding assumptions (Jo et al., 2010). Some studies reported that carrying capacity per unit area became even higher when management techniques were applied together with improvements in forage quality. For example, legume mixed sowing combined with manure application further increased estimated carrying capacity compared with manure alone (Table 1).

    In earlier studies, carrying capacity was calculated using a body weight of about 450 kg and a forage ratio of around 70% in the diet (Jo, 2012;Hwangbo and Jo, 2013). This approach has been used as a general assumption in many cases. However, actual farm conditions are not exactly the same. Feeding systems differ, and the forage proportion in the diet also changes depending on the farm. Because of that, using one fixed assumption for every situation may not fully reflect field conditions.

    In this study, body weight and forage ratio were adjusted to examine how the estimated values would respond. When lower body weight and a higher forage proportion were applied, carrying capacity per unit area tended to be higher. In contrast, when body weight increased and forage proportion decreased, the estimated value became lower. The difference appeared clearly in the calculation results.

    From these results, it can be seen that carrying capacity does not remain constant. The value shifts depending on how the assumptions are set. In practical terms, it seems difficult to treat it as an absolute standard. It may be more realistic to use it as a relative reference, and even then some adjustment would likely be needed according to local feeding practices and management conditions.

    Ⅴ. LIMITATIONS AND FUTURE RESEARCH DIRECTIONS

    Previous studies on livestock manure application have generally reported positive effects on improving forage crop productivity and forage value. However, when the literature is reviewed in an integrated way, several limitations can also be identified, and these points should be addressed in future research.

    First, many studies were conducted over a short experimental period. The effects of manure application may appear positive in the short term, but the long-term effects under repeated application can be different (Frick et al., 2022). Some studies reported that repeated manure application may lead to changes in soil chemical properties and accumulation of specific nutrients (Zhen et al., 2020). In particular, accumulation of nitrogen and phosphorus, salt build-up, and changes in soil reaction (pH) require long-term investigation (Feng et al., 2024). Therefore, future studies need to examine the long-term impacts of continuous manure application on soil and the environment.

    Research on differences in manure type and treatment method is also not sufficient. Some studies classified solid cattle manure, liquid cattle slurry, and liquid pig manure and evaluated their effects on forage crop productivity and soil response. However, direct comparisons among manure types are still limited (Na et al., 2006). Table 4 summarizes the characteristics of each manure type and general application trends.

    Livestock manure can show different nutrient use efficiency depending on its form and treatment method. The risk of leaching or nutrient loss can also differ (Niu et al., 2023). For this reason, future studies need experimental designs that allow direct comparisons among manure types. More studies are also needed to evaluate manure type together with treatment and application methods.

    In addition, most studies were conducted in specific regions or under limited field trial conditions, which makes regional comparisons difficult (Park, 2010;Oh, 2013). Even within Gyeongsangbuk-do, soil and weather conditions vary widely by area. These environmental differences can influence the effects of manure application. For example, Choi (2021) reported that forage crop productivity, forage value, and Hanwoo carrying capacity per unit area differed by region even under similar cropping and fertilization conditions. Therefore, multi-site trials are needed to confirm whether the results are repeatable and applicable under practical farm conditions.

    Evaluation of Hanwoo carrying capacity per unit area has the advantage of linking forage crop productivity and forage value to livestock farm management. However, the results can change depending on assumed values such as cattle body weight, forage feeding ratio, and management conditions (Hwangbo et al., 2015). Thus, this indicator is more appropriate for comparing treatments rather than being used as an absolute value (Qi et al., 2025). Future studies should confirm field applicability through on-farm demonstration trials. In addition, complementary indicators that can reflect different feeding and management conditions should also be suggested. The strengths and limitations of the reference-based Hanwoo carrying capacity index per unit area are summarized in Table 5.

    Future studies should consider soil changes, forage production, how forage is actually used, and Hanwoo carrying capacity together, rather than examining each part separately.

    This study was conducted as a narrative review, so some subjectivity in selecting the literature cannot be avoided. Comparisons between studies are also limited because crop types, field conditions, and manure application methods are not the same. Carrying capacity was calculated using defined assumptions for body weight and forage feeding. Since feeding and management conditions vary in practice, the values should be treated as comparative estimates rather than fixed numbers. For this reason, the results need to be interpreted carefully.

    Ⅵ. CONCLUSIONS

    This review summarized previous studies on the effects of livestock manure application on forage crop productivity, forage quality, and Hanwoo carrying capacity per unit area. In many studies, manure application was associated with increases in dry matter yield and forage nutritional value, including crude protein and TDN. However, the magnitude of these effects varied depending on crop type, soil condition, weather, and application rate.

    The estimated carrying capacity values were calculated based on assumed animal body weight and forage contribution. Therefore, direct application of these values to farm practice should be done with caution and adjusted according to local management conditions.

    In general, livestock manure application increased forage production and supported nutrient movement in crop–livestock systems. However, when manure is used, application rate, soil condition, and climate should be considered together.

    Future studies should not limit manure effects to forage yield only. Soil characteristics, forage crop productivity, forage utilization, and livestock performance need to be examined at the same time. More standardized field studies are also needed to understand long-term responses and to support practical use of livestock manure.

    Figure

    Table

    Forage yield and carrying capacity by fertilization treatment
    Note: Values shown here indicate the general range reported in studies comparing manure-treated plots with plots without fertilizer.
    Percentage increase was calculated as (manure − control) / control × 100.
    Changes in crude protein are presented as percentage point differences between treatments and controls.
    Carrying capacity (head/ha/year) was estimated based on the reported dry matter and TDN yields, following the feeding assumptions described in each study.
    Application rates follow the original study settings and may differ in terms of nitrogen equivalence depending on crop type and region.DM = dry matter; CP = crude protein; TDN = total digestible nutrients.
    Manure type and forage response
    Note: Yield change considered against control plots. DM yield and feed value were included in the assessment. DM = dry matter; CP = crude protein; TDN = total digestible nutrients.
    DM = dry matter; CP = crude protein; TDN = total digestible nutrients.
    Settings applied in Hanwoo carrying capacity studies
    Note: Jo (2012);Hwangbo and Jo (2013).
    Manure types used in forage research
    Note: Korean field studies (Lim et al., 2003;Shin et al., 1999;Song et al., 2006).
    Strengths and limitations of the Hanwoo carrying capacity per unit area index reported in representative Korean forage studies
    Note: The points summarized here are based on Jo (2012), Hwangbo and Jo (2013), Hwangbo et al. (2015), and Stone et al. (2021).

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