How to enhance soil quality in dryland farming systems in Indonesia (Review)

Soil quality is one of the factors that determines the sustainability of an agricultural system. The ability of types of soil to support the health and habitat of living things, maintain the production of plants and animals, and preserve the quality of the water and air is known as soil quality. Soil quality is not limited to agricultural land, but also includes how to maintain soil function as part of the ecology. In dryland farming systems, the issue of soil quality has become a concern of researchers and agribusiness actors because there are many problems related to dryland management systems, especially in Indonesia, where most farmers have not mastered good farming techniques. This paper presents a review of soil quality in Indonesian dryland farming systems and offers several solutions to improve soil quality through an agroecological approach.


Introduction
Indonesia is one of the countries in the tropical climate region that has dryland which is still very wide even though geographically this country is an archipelago.As one of the most important agricultural countries in Southeast Asia.Indonesia is a country in a wet tropical climate that has very large areas of dry land, even though geographically this country is an archipelagic country and is one of the most important agricultural countries in Southeast Asia.Land resource information plays an important role in supporting agricultural development planning.This resource information covers technical, socioeconomic, and cultural aspects, land law, and politics.All this information is very useful in preparing national development strategic plans.Based on data from BPS Indonesia, the national dryland area reaches 63.4 million hectares, which is around 33.7% of Indonesia's land area.The land that has been used as a dryland farming system is an area of 8.8 million ha, while the rest is used for plantations of 18 million ha and 26.3 million ha is land for shrubs.Several research results that have been carried out indicate that most of the dryland managed for agriculture has many constraints it is known as marginal land or sub-optimal dryland [1], [2].
Based on the characteristics and characteristics of each land typology, sub-optimal land can be divided into dryland and wetland [3].Dryland is further classified into acid dryland and dry climate dryland.Dryland with an acid reaction is also known as a land group consisting of acid mineral soils consisting of several soil orders, including Ultisols, Oxisols, Inceptisols, Spodosols, and Andisols [4].This group of soils is called variable charge and has also been studied by [5].Dryland with dry climates is found in Eastern Indonesia.In this type of dryland farming system from the aspect of soil quality, it is very different when compared to dryland typologies in wet climates [6].The most basic problem in dryland is low rainfall (generally <1,200 mm/year) so water management is important in this region.
The problems encountered in sub-optimal dryland farming systems are very complex, because in addition to being caused by low-quality soil characteristics, land management systems are not yet optimal [3], [5], [7].Indonesian specifically, the dryland management systems applied by farmers vary widely.Generally, dryland is managed in three land use patterns, namely for seasonal crop farming planted with food crops such as corn, soybeans, peanuts, upland rice, and various types of vegetable crops, managed for plantations such as oil palm, rubber, coffee, cocoa, and the like, and managed for mixed farming.The planting patterns applied can take the form of integrated agriculture, agroforestry, and others.
Except for the plantation system managed by the company, in general, the results of agricultural production found in dryland farming are still very low, so there is a need for technological innovation to improve soil quality and a better and more efficient management system.Related to the problem above, the author presents a review of several methods of managing soil quality in dryland farming systems, especially in Indonesia, this is based on the findings of the conducted research.

Materials and Methods
This article was written based on a review of several literary sources and reference books.The discussion provides a conceptual framework for finding various field and laboratory approaches and provides a basis for practical application in the management and improvement of dryland, especially dryland in tropical climate regions.The presentation also reviews the need to qualify soil quality and the nature of indicators of soil fertility, quality, and health as a function of land use, landscape, and climatic characteristics.A strategy to measure soil health and quality to ascertain if soil quality can sustainably adapt to dryland management techniques.
The discussion focuses on five basic issues, namely: (i) definition, and review of soil fertility, soil quality, and soil health, (ii) identification of physical and socio-economic constraints associated with managing soil quality in dryland farming systems, (iii) determining soil quality indicators, (iv) using models and assessments, and (v) strategies for managing and improving soil quality.The assessment also includes the relationship between soil threat targets, ecosystem functions, and services.

Soil Fertility, Soil Quality, and Soil Health
So far, soil quality has generally only been seen from the aspect of soil fertility which is associated with the ability of the soil to provide nutrients to plants.Numerous soil chemistry parameters relating to nutrient delivery are also used to evaluate soil fertility.In Indonesia, for example, to determine the status of soil fertility, especially in dryland systems, there are 5 parameters assessed, namely: CEC, base saturation, organic C, P2O5, and K2O reserves [8].Soil fertility status assessed from this parameter does not actually reflect ideal soil conditions because the characteristics and properties of soil are very complex because the soil is a dynamic system [9].Therefore, in the last decade, studies on soil fertility have expanded to the issue of soil quality.The point is that soil fertility is not only assessed from the aspect of plant nutrient supply but must also include soil properties that support sustainable agriculture.The intended agriculture is one that focuses not only on the sustainability of the agricultural system but also on production produced from agriculture which must be of healthy and safe value as a food product [10].
In this regard, the meanings of soil health, soil quality, and soil fertility continue to be developed by expanding study aspects and adding parameters or indicators to make them more comprehensive and holistic.This has been the theme of lengthy discussions by many soil scientists in order to develop more environmentally friendly and sustainable agricultural systems.To give one example, FAO strives to define soil fertility as the soil's ability to provide plants with necessary nutrients and groundwater in enough amounts and proportions for plant growth and reproduction in the absence of dangerous substances that could hinder plant growth [11].According to the definition of soil fertility, fertile soil is one that can support a diversified and active biotic population, present a distinctive soil structure, and permit disturbed decomposing [12].However, the concrete application of the idea of soil fertility is typically chemical and somewhat physical in terms of just giving nutrients and water to plants.
Perceptions about soil fertility then began to shift to a broader scope known as soil quality.Some experts try to propose new concepts regarding soil fertility to be expanded into soil quality.Physical, chemical, and biological characteristics of the soil are among the factors affecting its quality [13].In the present context, the ideas of soil fertility and soil health are combined under the umbrella of soil quality.
In contrast to soil quality, which focuses more on the dynamic soil features, soil evaluation looks at basic soil properties that cannot be changed and are frequently evaluated over the full profile which are greatly influenced by management, especially those that are often monitored in topsoil 0-25cm [14].However, while examining the direct relationship between soil quality and water quality, the study's soil attributes inherent in the soil profile section are developed into hydrological concerns and water quality features that are also engaged in the evaluation [15].Finally, the agricultural viewpoint on soil quality is the capacity of the soil to enable plant growth without harming the environment.
The term soil health refers to soil quality that affects animal and human health through plant quality which in some cases is often associated with disease problems [16].An analogy between the health of creatures or communities and soil health has also been used to demonstrate soil health [17].Soil quality is often defined as a soil's capacity to function as an essential living ecosystem that can sustainably support humans, plants, and animals [18].Discussions about soil quality and soil health soon emerged after the concept of soil quality came into question in the 1990s.Soil health, as opposed to soil quality, will consider the ecological features of the soil that have impacts beyond its quality to grow specific crops.This feature primarily relates to the biodiversity of the soil biota, the organization of the food web, and the operations and functions that the biota carries out.
The authors on this subject continue by explaining the difference between soil health and soil quality is that the former relates to the alive and dynamic aspects of soil.Therefore, they believe that although the ideas of soil quality and soil health overlap, the two terms are frequently used similarly [15].While soil quality is more concerned with the soil's ability to meet specific human demands, such as supporting the growth of specific plants, soil health is more interested in the soil's capacity to support plant development in order to preserve its function.Researchers use the phrase "soil quality," which encompasses both inherent and dynamic soil attributes, whereas farmers prefer the word "soil health," which is equal to dynamic soil quality [19].

Biophysical and Socio-economic Constraints in Dryland Farming
From a global perspective, dryland is a land condition characterized by scarcity of water thereby limiting two main interrelated functions, namely primary production, and nutrient cycles.In the long-term natural sources of moisture in the form of rainfall or precipitation are offset by moisture loss through evaporation from the soil surface and transpiration by plants which are known as evapotranspiration [20].Cattle, people, and both natural and managed ecosystems are all significantly impacted by this potential water deficit, which also affects how much food, fodder, and other crops can be produced [21].A dryland is defined as an area with a drought index value of less than 0.65 [22].An aridity index (AI) value lower than 1 indicates an annual moisture deficit.In a world map, this aridity index is defined as an area with AI≤0.65, that is, an area where the annual average potential evapotranspiration is at least 1.5 greater than the annual average rainfall [23].Dryland is not evenly distributed between poor and rich countries.Only 28% of the world's dryland area is in countries with a developed economy, while more than 72% is located in developing nations.Additionally, the percentage of dryland held by emerging nations rises as aridity increases to nearly 100% in very dry locations.As a result, most upland people live in developing countries (87-93%), and only 7-15% live in industrialized countries.Figure 1, illustrates how many drylands are all over the world.
Indonesia is a country located in a tropical climate zone, and the perception of dryland is very different from the global context.The definition of dryland has more connotations of a land management system where water needs are insufficient during the growth of cultivated plants.Insufficient water is not synonymous with dryland systems in dry climates because the ratio between precipitation and water loss through evapotranspiration (AI) is >1 [23].Agricultural systems in the tropics like this are better known as dryland farming systems [4].Farmers generally do not manage water well, so in certain months there is a deficit in the balance of water demand while in other months there is an excess.They demonstrate a gradient of increasing primary productivity that covers subhumid drylands to hyper-arid, arid, and semi-arid lands [25].4) It is anticipated that due to population growth, changes in land use, and a changing climate, the issue of water supply and shortfall in drylands would occasionally get worse.An average of 25% more fresh water is used globally every ten years, and this pressure will impair agricultural land productivity and freshwater availability, which will have further negative effects on human wellbeing in dryland areas.(5) There is a strong likelihood that changes in land use, land cover, and the global climate will hasten the declines in water availability and biological production in drylands.(6) Extreme reduction of pasture vegetation cover through forage grazing and gathering of firewood exposes the soil to erosion.(7) Among the arid land sub-types, semiarid ecosystems, and populations are the most vulnerable to loss of ecosystem services.(8) From 10 people per square kilometer in dry dryland to 71 people in sub-humid dryland, population density in dryland fell with increasing dryness.Contrarily, as the aridity of a region increases, so does the susceptibility of its dryland ecosystems to human actions that worsen the state of its land.(9) Dryland deterioration is believed to be between 10 and 20 percent worldwide, and current traditional management techniques help ensure that ecosystem services are used sustainably.

Soil Quality in Tropical Drylands
Dryland farming is an agricultural system that is carried out in areas that have low rainfall and limited water availability.Dryland has less than optimal potential to support plant growth, especially in waterstress conditions.This poses its own challenges in utilizing dryland for sustainable agricultural activities in the future.In Indonesia as a country located in the tropical climate zone, dryland is divided into two different typologies.The first typology is dryland found in areas with limited rainfall or areas with rather dry climates.Areas belonging to this group are in Eastern Indonesia such as the islands of Lombok, Sumbawa, Flores, and Timor Island with an annual average rainfall of <1,200 mm/year.The main problem in this area is the water deficit for most of the year so it is not sufficient for cultivated plants, especially food crops or annual crops.Several soil types in this region react slightly alkaline or are potentially affected by soil salinity [6].The distribution of dryland in this dry climate region is relatively small or less than 10% of Indonesia's total dryland.This dryland generally consists of dry scrub vegetation, savanna grasslands, or highlands that do not have enough water to support irrigated agriculture.To support agricultural businesses in this region, it is enough to build a good technical irrigation system that meets water needs and proper soil management [5].Cultivation techniques that are commonly used in dryland include conservation tillage, planting plants with sufficient spacing, crop rotation, and the use of organic fertilizers and green manures to maintain soil fertility.Limited availability of water is a major challenge for agriculture in dryland.Drip irrigation or spring-based irrigation, for example, are appropriate irrigation methods that are required to support dryland agriculture.
The second typology of dryland is tropical dryland which is found in a climate zone with moderate to high rainfall, known as the humid tropical zone.This zone occupies more than 2/3 of dryland (82%) in Indonesia, which is more than 144.47 million hectares [3].This dryland is also known as acid dryland or acid mineral soil because most of the soil has a problem with acidity some researchers call these soils low clay activity soils and are included in variable charge soils [5].Acidic dryland is generally located in areas with relatively high rainfall or more than 2,000 mm per year with several wet months which reach more than six months.This causes the level of nutrient leaching to take place intensively and results in acid-dryland having a low level of fertility.Acidic dryland has a low pH of less than 5.5, which affects the available nutrient content for plants and soil cation exchange capacity (CEC) [4].One of the problems that often occur in acid-dryland is the high content of soluble Al which is closely related to low soil pH which inhibits plant growth [6].It is called soil with low clay activity because it has a low negatively charged colloid system and a low CEC because the soil component is generally composed of Fe and Al hydrous-oxide which have a low colloidal surface charge [26].The research results show that the characteristics of dryland, among others: (1) High rainfall but limited water availability.This occurs due to the inability of farmers to manage and utilize water from existing rains so that when entering the dry season, plants experience a shortage of water (water deficit) [27].(2) Poor soil and low nutrient content.Most tropical drylands have low-fertility soils [3].This happens because with high-intensity rainfall there has been very intensive leaching of nutrients so that the soil becomes nutrient-poor.This indication is also reflected in the low level of soil fertility which is characterized by low SOC [28], low CEC and BS, and poor soil physical properties [5].(3) High soil erosion rate.Dryland usually has moderate to severe erosion.This erosion occurs in addition to being caused by hilly to mountainous land surface shapes and has high erodibility making it susceptible to erosion [29].(4) The soil quality index is generally low.Some research results on tropical drylands show that the soil quality index (SQI) is low [30].The low SQI is partly due to poor soil texture and porosity, availability of nitrogen, phosphorus, and potassium, as well as organic C content and a low number of microorganism populations.With the many constraints found in dryland farming systems, this land is better known as marginal land or suboptimal dryland [6].

Indicators of Soil Quality
In order to ensure the sustainability of the ecosystem and provide advantages to humans, soil quality is clearly related to human-soil interactions.Recently, soil quality assessment has also been included in similar land evaluation procedures that are now applied in sustainable land management [30], risk assessment, monitoring of environmental change [31], and land restoration.The land potential has been considered over the long term and is dependent on topography, climate, and natural soil qualities.It can also be changed depending on the weather and dynamic soil features and integrating soil quality and land appraisal should highlight how crucial land is to human well-being.
The focus on land quality has been extended to quality and soil health, which are both innate and dynamic properties.In this context, the function of the land needs to be seen from various aspects of its use for humans and the environment as well as the threat to the land itself.The relationship of the three components by [15] is illustrated in Figure 2.  Figure 2 shows that threats to soil can occur in various forms, namely: loss of biodiversity, contamination, sealing, compaction, landslides, erosion, reduction of soil organic matter (SOM), pollution, salinization, and inundation [32].This threat will affect soil functions as a habitat for organisms, a source of nutrients, water, and carbon storage.It is therefore necessary to take preventive, control, and corrective measures.The approach to soil quality and health is different from a reductionist approach, regarding the measurement of soil properties and process indicators.Although from the practical point of view, such measurements are still important, the definitions of soil quality and soil health also consider emergent system characteristics such as the interactions between soil organisms and soil structure and adaptability to changing conditions.[15] Table 1 shows that several indications can be used to assess soil quality.Biological indicators include earthworm population, N mineralization, microbial biomass, and soil respiration, while soil chemical indicators include labile C and N content, micronutrients, salinity and sodicity, secondary nutrients Ca, Mg, and S, heavy metals, available N and total N, CEC, electrical conductivity (EC), available K, available P, pH, and total organic/cationic matter.Infiltration, aggregate stability, porosity, hydraulic conductivity, resistance to penetration, depth, texture, bulk density, and water storage are among the physical characteristics of soil.When viewed from all the indicators above, in summary, it can be said that there is numerous chemical, physical, and biological indicators of soil quality.

Improvement Soil Quality of Dryland
As described in the introduction, the primary issue on dry land, especially in humid regions, is the low level of soil fertility [1].The success of your farming business largely depends on the soil's quality.Therefore, soil improvement is an important concern for farmers, and not all types of soil are suitable for fertile farming.Not all areas of the world have fertile soil.Therefore, it is fortunate that some areas of the world have fertile soils such as those found in parts of Europe, New Zealand, and the United States.In contrast, on the continent of Africa, Latin America, and West Asia, countries in Southeast Asia and parts of Australia have less fertile soils, so a good and efficient land management system is needed.
However, to implement a plan to improve soil quality, farmers, and agricultural practitioners, especially dryland farming, must first understand what is the problem with regard to soil quality or its deficiency [33].We can access and show a soil landscape map to give us an idea of the predominant soil types in our area and need to do some soil analysis.An effective soil analysis will provide the necessary basic knowledge about the characteristics of the soil.Once this information is obtained, we can begin to develop an effective soil nutrient management plan that optimizes crop production.There are many methods that can be used for managing plant nutrition and improving soil fertility.There are 5 (five) ways to improve quality while simultaneously increasing soil fertility and plant nutrition, namely: (i) giving and returning organic matter, (ii) applying biochar, (iii) mulch application, (iv) applying plant mixture, and (v) application of green manure.

(i) Application of organic matter
The most crucial and efficient strategy to enhance and maintain soil quality is to add and return new organic matter each year.Regular organic matter input promotes soil structure [34], enhances the capacity to store both nutrients and water [4], [35], defends soil from erosive and compacting forces [36], supports a healthy population of soil microorganisms, increases plant resistance to water and nutrient stress [27], and increases nutrient solubility from mineral binding [37].Leaving agricultural waste in the field, selecting crop rotations that include high residue crops, planting cover crops, utilizing manure or compost, and other techniques can all help enhance organic matter, employing soil-based rotation, mulching, soil-based low or no-till systems, and soil-based low or no-till systems [38].The administration of this organic material can also be given in combination with the type of amendment material and the dosage [4].

(ii) Provision of biochar
Biochar is a solid material containing high carbon (C) arising from the incomplete combustion or pyrolysis of organic waste [39].Biochar is very effective in restoring lost C from the soil because it contains 45-60% C depending on the material used [34].In Indonesia, the potential for using biochar is enormous considering that raw materials such as coconut shells, rice husks, cocoa pod husks, oil palm shells, corn cobs, and other similar materials are widely available.According to extensive research, biochar is an organic substance with stable qualities that can be utilized as a dryland soil amendment.As an organic amendment, biochar can also improve crop yields and reduce greenhouse emissions.

(iii) Mulch application
Mulch is a material used to cover farmed plants to keep the soil moist and prevent weeds and disease from growing so the plants can thrive.In general, the function of mulch is to protect the soil from the destructive power of raindrops.Increases water absorption by the soil.Reducing the volume and speed of runoff (reducing erosion).Mulch can be permanent, such as wood chips, or temporary, such as plastic mulch.Mulch can be in the form of organic mulch and inorganic mulch.In the context of improving soil quality, organic mulch is recommended as mulch.The advantage of organic mulch is that it decomposes quickly, is easy to obtain, and is more economical so that the nutrients in the soil become more abundant.The use of organic mulch with straw and bamboo leaves can reduce soil temperature [40].

(iv) Mixed cropping
Mixed crops are plantations consisting of several plants that grow without adjusting the spacing or array.By selecting the right plants, this system can provide several benefits, including reducing attacks by plant-disturbing organisms, increasing soil fertility, increasing soil nutrient content if leguminous species are used due to the presence of Rhizobium bacteria in root nodules [41], improving soil structure and aeration, and will obtain diverse yields and increase the harvest index and land equity ratio [29].

(v) Green manure
Green manure is fertilizer derived from the decomposition of plant residues.In the world of agriculture, green manure is being looked at again as a potential source of organic matter considering that agricultural land is currently experiencing degradation.Sources of green manure can come from crop residues, hedges, ground cover plants, and wild plants such as the Lantana camara, Tithonia diversifolia, Cromolaena odorata, and Ageratum conyzoides, as well as Sesbania rostrata [41].Green manure can maintain a good ecological cycle, and physically improve soil structure, chemically increase nutrients, and biologically increase the activity of soil microorganisms so that the soil environment becomes good.In addition to the five methods above, several other technologies can also be applied, such as biofertilizers, soil and water conservation, and implementing integrated farming systems.

(vi) Biofertilizer)
Biofertilizer is a method of improving soil quality by using fertilizers containing certain microbes by supplying and increasing the supply of nutrients, as well as helping plants deal with pathogen attacks.Application of biofertilizers, for example by utilizing Rhizobium bacteria, PGPR [36], mycorrhiza [42], and bio-compost applications [43].

(vii) Soil physical improvement
The physical improvement of the soil referred to here is implementing good soil and water conservation practices, for example controlling erosion and run-off, preventing open soil, improving compaction, conservation tillage, improving structure and aeration, as well as implementing conservation agriculture on drylands such as alley cropping, agroforestry, multiple cropping, and silvopasture [29].

(viii) Integrated agriculture
Integrated agriculture (farming) is utilizing dryland with an integrated cultivation system between plant cultivation, animal husbandry, fisheries, and forestry as well as tourism (tourism).This method provides many benefits economically, socio-culturally, and in harmony with the environment /ecosystem.

Conclusions
The main issues with Indonesia's dry land farming system are inadequate water requirements, bad growing methods, and poor soil quality.From the aspect of soil fertility, the main problems in drylands are acid soil conditions, nutrient deficiencies, scarcity of organic matter, and erosion.It is necessary to improve soil quality in tropical drylands in a planned manner by evaluating indicators, choosing significant limitations, and implementing appropriate technologies.Applications of organic matter, biochar, compost, biofertilizer, and organic mulch, as well as conservation and integrated farming systems, are good technologies to be used with dryland farming systems.

4 Figure 1 .
Figure 1.Map of the World's Drylands (https://www.fao.org/dryland-assessment2023)Regarding dryland farming systems, it explains that there are several important matters concerning global issues on dryland, including:(1) Drylands makeup around 41% of the earth's land surface, and more than 2 billion people, or roughly one-third of the world's population, reside there.(2) There is a high degree of confidence that the average dryland people lag beyond the rest of the globe in terms of indicators of human development and well-being.(3) The dryland community is currently significantly behind individuals in other areas in terms of socioeconomic status, with 90% of them living in underdeveloped nations.(4) It is anticipated that due to population growth, changes in land use, and a changing climate, the issue of water supply and shortfall in drylands would occasionally get worse.An average of 25% more fresh water is used globally every ten years, and this pressure will impair agricultural land productivity and freshwater availability, which will have further negative effects on human wellbeing in dryland areas.(5) There is a strong likelihood that changes in land use, land cover, and the global climate will hasten the declines in water availability and biological production in drylands.(6) Extreme reduction of pasture vegetation cover through forage grazing and gathering of firewood exposes the soil to erosion.(7) Among the arid land sub-types, semiarid ecosystems, and populations are the most vulnerable to loss of ecosystem services.(8) From 10 people per square kilometer in dry dryland to 71 people in sub-humid dryland, population density in dryland fell with increasing dryness.Contrarily, as the aridity of a region increases, so does the susceptibility of its dryland ecosystems to human actions that worsen the state of its land.(9) Dryland deterioration is believed to be between 10 and 20 percent worldwide, and current traditional management techniques help ensure that ecosystem services are used sustainably.

Table 1 .
Several indicators of soil quality from aspects of soil physics, chemistry, and biology