Integrated Nutrient Management (INM): Concept, utility and importance in sustainable agriculture

Introduction

The vision of a world free of hunger and poverty, which is made more challenging by rising living standards in rural areas where the majority of the impoverished reside and their complete reliance on agriculture to meet their food needs, is the primary challenge facing agriculture planners and farming decision makers in the upcoming years. The key to eliminate the current suffering lies in the creation of a strategic plan that enhances prosperous farming and enables farmers themselves to achieve agricultural growth, reduce poverty, and sustain high returns. Therefore, the following question will be the primary problem in the approaching years. Can agriculture provide all of the world's population's anticipated food needs? (FAO, 2012) [1] . To meet the world's future food security and sustainability needs, food production must grow substantially while agriculture's environmental impact must decrease dramatically at the same time. Global food production must increase by 70% by 2050 to fulfil the increasing demand (Foley et al., 2011) [2] . In order to meet this challenging target, an average annual increase in cereal production of 43 million metric tonnes per year is required. With the view of an increase in land scarcity and water shortage, most of the agriculture plans depend on the use of chemical fertilizers and the production of new high-yielding crop varieties. Yet, both components are much expensive and will lead to higher pressure and more responsibilities for the financial investments and consequently will lead to an increase in the total costs. Meanwhile, the price of fertilizers increases, year by year, due to the higher amount of fertilizers needed in the second and third seasons as compared with that in the first season to maintain the current yield production at economical level. Despite the increase in the quantity of fertilizer application, a part of applied fertilizers and soil native nutrients were already consumed by the current and previous crops, especially in the case of intensive agriculture, where two to three crops are annually cultivated. Moreover, application of inorganic fertilizers is not a pragmatic option for many poor farmers in different regions worldwide, because many poor farmers do not have enough money to pay the claim of fertilizer price, besides its scarcity and un availability in times of need. Since ancient times, farmers have known that soil health can be restored by applying organic manure; accordingly, they used to apply farmyard manure regularly and directly after crop harvest. Using organic manures post-harvest is linked to improved soil health and enhanced physical, chemical, and biological properties, especially in marginal soils with low organic matter and nutrient content (Selim, 2018) [3] . No single nutrient source chemical fertilizers, organic manures, crop residues, or bio-fertilizers can meet crop needs in intensive agriculture. Integrating these sources is key to boosting soil fertility and crop productivity. Integrated Nutrient Management (INM) safeguards soil health and reduces reliance on chemical fertilizers, offering economic benefits (Wang et al., 2019; Song et al., 2020) [4,5] . Organic manures improve soil structure, and INM balances food security with environmental sustainability, impacting crop yield, soil quality, and greenhouse gas mitigation.

Need of Integrated Nutrient Management (INM)

• Prolonged use of chemical fertilizers, particularly those high in nitrogen, is degrading soil quality and exacerbating issues related to poor nitrogen use efficiency.

The concept of Integrated Nutrient Management (INM)

Integrated Nutrient Management (INM) combines traditional and modern methods to create a sustainable farming system that optimizes nutrient use from organic, inorganic, and biological sources. According to FAO (1998) [1] , INM maintains or adjusts soil fertility to achieve a given level of crop production by leveraging all possible sources of plant nutrients. INM involves balancing inorganic, organic, and biological resources to sustain yields, preserve soil health, and provide environmentally friendly crop nutrition solutions. The goal is to utilize every available nutrient source wisely, synchronizing nutrient demand and release while minimizing losses. This approach reduces leaching, runoff, and emissions, achieving high nutrient-use efficiency (Zhang et al., 2012) [6] . In order to increase agricultural output and reduce land degradation, it also seeks to optimize the physical, chemical, biological, and hydrological characteristics of the soil. More people are now aware that INM can simultaneously and nearly invisibly protect soil resources in addition to increasing crop output. In order to preserve available water and increase plant nutrients, its methods make use of farmyard manures, farm wastes, soil amendments, crop residues, natural and chemical fertilizers, green manures, cover crops, intercropping, crop rotations, fallows, conservation tillage, irrigation, and drainage. In order to reduce nutrient losses and enhance plant absorption, this strategy also incorporates novel methods such deep fertilizer application and the use of urea coatings or inhibitors. Such practices encourage farmers to focus on long term planning and have greater consideration of environmental impacts, rather than only focusing on yield-scaled profit. The main objective of integrated nutrient management is to maintain economic yield for a long time with minimal impact on native soil fertility and pollution, as well as to raise farmer awareness of eco-friendly techniques (organic farming system) for producing healthy, contaminant-free food while ensuring adequate financial returns

Components of INM

Organic manure: Well-decomposed organic manures, such as farmyard manure, digested cow dung, and compost (both urban and rural), were supplanted by chemical fertilizers as the most efficient source of plant nutrients with the advent of the Green Revolution. It is now essential to resume adding these manures. Organic manures include micronutrients, which are substances that both stimulate and impede growth, in addition to primary and secondary nutrients. However, some materials used to create urban waste compost, rural compost, and farmyard manure contain dangerous elements such heavy metals like Ni, Cr, and Cd, which can have a detrimental effect on plant growth if they are present in sufficient amounts in organic manures. Furthermore, there are a number of industrial by-products and municipal trash that have a reasonable nutritious potential. These nutrient-carriers, on the other hand, have not been thoroughly tested to determine their fertilizer equivalents. These sources must be integrated based on their availability in various crops and cropping systems. Industrial wastes such as spent-wash from distilleries, molasses, pressmud, and other sugar industry byproducts, as well as wastes from other food processing businesses, have a high manurial value (Das et al., 2015) [7] . Organic manures release nutrients gradually, ensuring a continuous supply of nourishment for plants. They also enhance soil microbial activity, which plays an essential role in nutrient cycling and organic matter decomposition. Moreover, organic manures improve soil aeration, water retention, and root penetration, contributing to better crop growth and yield. Bio-fertilizers also produce beneficial compounds, boosting plant growth and resilience. Biofertilizers are the preparations containing microorganisms beneficial to agricultural production in terms of nutrient supply especially N and P. The bio-fertilizer is a carrier-based microbial inoculant that contains effective living microorganism cells. Biofertilizers have the ability to fix atmospheric nitrogen in ammonia form, mobilize nutrients, solubilize insoluble nutrients in the soil system, and release plant growth hormones that are essential for plant development and growth. The two main organic fertilizers for rice that can be used in place of chemical fertilizers are Azolla and blue-green algae (BGA). Particularly in rice soils with standing water, BGA can fix atmospheric nitrogen and release growth-promoting compounds. Biofertilizers are the products containing living cells of different types of microorganisms that have an ability to fix/mobilize nutrients from non-usable form through biological processes. These microorganisms are capable of mobilizing non-labile nutrients to plant roots. These also secrete some growth promoting substances. These micro-organisms are used for the treatment of seeds, seedlings and application to soil or in composting to increase soil fertility and help in crop growth and high yield. Vesicular Arbuscular Mycorrhizae (VAM) is the symbiotic association of fungi with roots of vesicular plants with great potential in acquisition of P in P deficient soils and solubilization of unavailable P in the soil. The plant roots transmit substances to the fungi, and the fungi aid in transmitting nutrients and water to the plant roots. The mycorrhizal fungi carry out its functions by expanding surface area of plant root system by 10 to 1000 folds into the soil through their ramifying hyphae. The hyphae reach wetter soil areas and help plants to absorb nutrients, particularly the less available mineral nutrients like phosphorus, zinc, molybdenum and copper etc. Green manure: Growing legumes as green manure to improve crop productivity and soil health is among the oldest practices. It gains more advantages, especially for light soils with sandy and loamy sand textures, as well as sandy loam soils or soils with a loam/silty loam texture. Although they may serve other purposes as well, green manures are crops planted particularly to improve and preserve the fertility and structure of the soil. In these circumstances, growing dhaincha (Sesbania aculeata) and burying it in the soil before the flowering stage at the time of transplanting rice has been found effective in raising the yield of both rice and wheat. difference in soil bulk density (Saha et al., 2010) [26] . The main reason for decreasing bulk density under INM was aggregation of soil particles due to increasing organic matter as well as stability of aggregates which leads to an increase in the total pore space in the soil.

Eco-friendly practices:

The massive change in ecosystem mostly attributable to the widespread use of synthetic fertilizers and pesticides, particularly in the intensive agriculture system (Peng et al., 2010). As a result of their long-term use in some developing nations, chemical fertilizers, notably nitrogen, phosphorus, and potassium (NPK), are an important factor and primary source of environmental contamination and land erosion (Davidson et al., 2014) [25] . INM technique that can minimize environmental degradation and continue to be the most effective way to achieve food security, enhance environmental quality, and fulfill ever increasing food demands without causing negative consequences. Integrated nutrient management is a simple system that can create a favorable soil condition and provide plants with a sufficient, efficient, and sustainable nutrient source. It is also a promising strategy that has made significant contributions to reducing negative environmental impact, increasing both the quantity and quality traits of global food supplies, and expanding land with a plan of sustainable and economical agricultural development.

Carbon sequestration: Enhancing carbon sequestration through integrated nutrient management can be achieved by exploring soil management practices, investigating the role of plant-soilmicrobial interactions, exploring the integration of agroforestry practices, developing precision nutrient management techniques, and using modeling tools and decision support systems. Soil management practices that promote carbon sequestration include the use of organic amendments, cover crops, and crop rotations. These practices can help to increase soil organic matter, which is a major sink for atmospheric carbon. Beneficial soil microorganisms, such as mycorrhizal fungi, can help to improve nutrient uptake, promote root growth, and enhance soil aggregation.

Carbon sequestration: Soil organic matter is the most important indicator of soil fertility, quality and productivity and is usually estimated by determining soil organic carbon. It is generally believed that fertilizer application increases residues, including roots, returned to the soil, and as a result, can increase organic matter content and C sequestration. The INM through green manuring, crop residue incorporation and other animalbased manures has a profound influence on soil carbon stock. The direct application of organic manure to the soil, which encouraged the development and activity of microorganisms, as well as improved root growth, which led to increased biomass output, crop stubbles, and residues, are both associated with increasing the amount of organic carbon in the INM (Moharana et al., 2012) [27] .

Greenhouse Gas Emission (GHG): Worldwide, agriculture and related systems are thought to be a significant source of greenhouse gas emissions (Ravikumar et al., 2021) [29] . Reducing excess nutrient application and applying nutrients in a balanced manner are the main ways to lessen its contribution. In most farmlands, ambiguous methods applying plant nutrients to increase crop yields has become a confusing procedure. Conversely, one of the main causes of anthropogenic greenhouse gas emissions in croplands is the uneven application of fertilizer.

Therefore, to keep these anthropogenic GHG emissions under control, devising, and practicing proper fertilizer management is essential (Carlson et al., 2017) [28] . Of the several means of nutrient management, INM is proven better at minimizing GHG emissions. In INM, nutrient recycling and reuse strategies efficiently capture and recycle nutrients from various sources, such as agricultural residues, livestock manure, and wastewater. Practices like anaerobic digestion, composting, and biochar production can be used to convert these nutrient-rich materials into valuable organic amendments. Intercropping and crop rotation can also be made an integral part of INM systems that incorporate nitrogen-fixing crops can also reduce the need for synthetic nitrogen fertilizers and decrease nitrogen runoff.

Conclusion

Farmers have extensive experience using various organic material sources in an integrated and effective manner to maintain soil fertility and generate moderate crop yields through conventional farming methods. However, during the past 20 years, nutrient management has increasingly evolved to an excessive reliance on chemical fertilizers in order to attain food security with diminishing land and other resources. The longterm viability of the agricultural system is threatened by the increased prevalence of over-application of N in intensive agricultural areas, which results in low nutrient-use efficiency and environmental contamination. The practice of INM includes all possible sources of plant nutrients to optimize nutrient inputs, spatial and temporal matching of the soil nutrient supply with crop demand and reducing N losses while improving crop yield. Interaction of agricultural inputs leads to increases in crop productivity while substantially reducing N losses and GHG emissions, judicious application of mineral and organic fertilization with higher resource-use efficiency, enhance the soil-plant-microbes-environmental sustainability.

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