Agricultural soil quality and integrated nutrition management

The agricultural quality of soil (CS) reflects its ability to sustain biological productivity and delves into the soil attributes that influence the interaction of soil with the environment, with the provision of nutrients, with photosynthesis and crop growth (^{Wilson and Sasal, 2017}). In recent decades, the concept of CS has evolved towards the concept of ‘soil health’, in which the ecological attributes of soil that have implications beyond its ability to produce a particular crop are captured (^{Bünemann et al., 2018}).

Particle size, aggregate stability (EA), bulk density (DA), structure (^{Zornosa et al., 2015}), texture, depth, hydraulic conductivity, water retention capacity (CRA) and porosity (^{Navarrete et al., 2011}; ^{García et al., 2012}) are among the most important physical properties of the soil. Physical properties indicate how soil accepts, infiltrates, retains and provides water to plants, factors that influence root growth, emergence of seedlings, movement of fauna in the profile and exchange of gases (^{Etchevers et al., 2009}).

Chemical attributes, such as total and labile CO, total and mineralizable N, pH, electrical conductivity (CE), CIC, etc., affect the availability and quality of water, the availability of nutrients for plants and microbes and the buffering capacity of the soil (^{Navarrete et al., 2011}; ^{García et al., 2012}). It should be noted that COS is related to soil organic matter (MOS) and in the holistic and preventive approach of sustainable agroecosystems, MOS is fundamental (^{Gupta et al., 2017}) because it is a storehouse and source of nutrients, improves soil properties, provides beneficial microbes that make nutrients available, stimulate plant growth and suppress pathogens (^{Hernández et al., 2014}; ^{Masunga et al., 2016}). The biological and biochemical properties of the soil such as C and N of microbial biomass (CBM and NBM), basal respiration (RB), enzymatic activities, DM, AM, etc., indicate early changes in MOS and in nutrient recycling and dynamics (^{Navarrete et al., 2011}; ^{Fuentes et al., 2016}).

In several crops with MNI, improvements in soil fertility have been reported, for example, in the rice system (Oryza sativa), wheat (Triticum aestivum), with the application FMs + 12 t ha^-1 of Cp, the availability of N, P, K, Ca and Mg increased, while the pH and the adsorption of Na of the soil decreased, which is explained by the formation of acids, release of Ca and leaching of Na (^{Sarwar et al., 2008}). In addition to increasing nutrient content, MNI with fungal residues + FMs buffered soil acidification caused by FMs in rice cultivation (^{Shi et al., 2019}).

In the cultivation of soybean (Glycine max) and wheat, the application for 21 years of FMs + farm manure (EG) led to better levels of extractable micronutrients (Fe, Mn, Zn and Cu) compared to FM (^{Choudhary et al., 2018}). Regarding residual soil fertility, in wheat with MNI (8 t of Cp ha^-1), in current (year 1) and residual (year 2) trials, the available P increased 162 and 173%, MOS 108 and 104%, interchangeable Ca 16. 7 and 17. 4% and CIC 15.4 and 17.1%, respectively (^{Demelash et al., 2014}). The residual soil fertility of the wheat crop benefited from MNI which included the use of 100% FM + EG + Azotobacter + Zn + Mn + Fe (^{Singh et al., 2017}).

The MNI of rice-wheat and cotton (Gossypium hirsutum) wheat systems, with the inclusion of Cp of municipal residues, DA and penetration resistance improved, and there was no accumulation of heavy metals (zinc, cadmium, chromium, lead and nickel) (^{Qazi et al., 2009}). With the inclusion of biochar in MNI, in addition to improving CS, heavy metals are immobilized (^{Šimanský et al., 2019}). MNI also improves the biological attributes of soil. ^{Liu et al. (2017)} tested in rice paddies an index that included the available nutrients, CBM and enzymatic activity involved in the cycles of C, N, P and S and found that with the use of FMs + pig manure, the highest score was obtained (0.85), compared to the control (0.72) and with the FM alone (0.77), FM + green fertilizers (AVs) (0.81) and FM + straw (0.79).

In the cultivation of corn (Zea mays), with FM + Vc, the highest improvements in terms of CIC, water availability and P were obtained, this was because the Vc stimulated AM, nutrient mineralization and secretion of enzymes of the roots (^{Doan et al., 2015}). The MNI with bokashi, in the cultivation of corn, increased the mycorrhizal colonization (^{Álvarez-Solís et al., 2010}) as well as the CBM (^{Bautista-Cruz et al., 2015}). The use of Cp + bacterial fertilizer increased the diversity of bacterial and fungal communities in maize (^{Zhen et al., 2014}). In bananas (Musa paradisiaca), with MNI (recommended 50% FM + 1 250 kg of MO ha^-1), bacterial diversity, pH and acid phosphatase activity increased, but as the application of FMs increased, these soil attributes decreased (^{Sun et al., 2018}).

^{Srivastava et al. (2012)} reported that in citrus plantations the gradual change of FMs to AOs favored DM. With MNI in tomato (Lycopersicom esculentum), MOS, labile C (^{Ren et al., 2014}) and RB (^{Hernández et al., 2014}) increased. Long-term MNI studies show a positive effect on COS and on the physical properties of the soil. In that sense, ^{Cai et al. (2019)} applied MNI in the rice-wheat system and observed that during the first 10 years the COS increased and then stabilized in the following 15 years. In another study, with the application for more than 40 years of FMs + 15 t ha^-1 of EG in the rice-wheat system, the CO level was maintained, and some physical properties of the soil were improved, such as DA, hydraulic conductivity and CRA (^{Pant et al., 2018}), but the zinc content decreased (^{Ram et al., 2016}).

In another work, the MNI with FMs + 5 t ha^-1 of EG, after 41 years of treatment, increased the size and stability of soil aggregates (^{Tripathi et al., 2014}). Through a meta-analysis elaborated with results of research carried out from 1989 to 2016, it was detected that in the rice-wheat system under MNI, the pH increased with respect to the control (without FMs or AOs), by 1.15% in the soil of the rice crop, but in wheat it decreased 0.55%, in addition the COS increased 23.2% and 16.2% with respect to the application of FMs alone in rice and wheat, respectively, the MNI also increased the NBM and the CBM. It should be noted that the effects of MNI were influenced by soil type, since the differences found in pH, NBM and CBM were greater in loamy-clay soil than in clay soil (^{Sharma et al., 2019}).

Integrated nutrition management and productivity of agricultural crops

The benefits of MNI on CS help to create sustainable agrosystems (^{Cai et al., 2019}), this is maximized in unproductive soils, since the production and application of large quantities of AOs would require covering high labor costs and sometimes the availability of raw materials is limited (^{Wang et al., 2015}). In the cultivation of corn, with the application of 50% FM + AOs (compost, bokashi and worm humus), the yield increased by 3.8, 12.7 and 11.5% compared to 100% FM, while with 100% FM + AOs, the increase was 17.7, 21.9 and 30.5%, respectively (^{Álvarez-Solís et al., 2010}).

In another study of MNI, some parameters related to crop yield were evaluated in maize plants, and the highest values of plant height, dry weight, leaf area index, photosynthesis and stomatal conductance appeared with the application of EG + FMs (^{Efthimiadou et al., 2010}). Also, the absorption of nutrients (N, P, K, Zn, Fe and Mn) increased with the MNI (FMs + EG + solubilizing bacteria of P + Azotobacter + Zn + Fe + Mn) (^{Singh et al., 2017}). In mustard cultivation, the radius, index and duration of the leaf area, the net assimilation rate (net exchange of CO₂ per unit of leaf area), chlorophyll, photosynthesis and growth of the crop were higher with MNI (75% FM + Vc at 2.5 t ha^-1) compared to that obtained with 100% FM (^{Mondal et al., 2017}).

On the other hand, in the tomato cultivation with MNI (60% FM + Cp, Vc or AVs), yields of fruits, height and dry weight of plants similar to those obtained with 100% FM were obtained (^{Hernández et al., 2014}; ^{Ilupeju et al., 2015}). With the addition of biofertilizers in the MNI, the improvements in yields are even greater (^{Chatterjee et al., 2014}; ^{Verma et al., 2015}); for instance, MNI with Cp inoculated with Trichoderma leads to a yield 43.8% higher than with FM (^{Abedin et al., 2018}). It has been observed that the application of poultry manure + N mineral in the cultivation of chili (Capsicum annuum) increased the soil temperature, which accelerated the enzymatic reactions related to the ripening of the fruits (^{Macías et al., 2012}).

A 25-year evaluation (1991 to 2015) with the application of EG + FM showed that the average yields of wheat and corn (1.6 and 5.8 t ha^-1) were higher than with FM (0.97 and 2.65 t ha^-1), respectively. In another study, with 30 years of MNI of soybean and wheat, yields were higher than with FM; however, even with MNI, yields declined over time, possibly because the available P, K and Zn decreased (^{Bhattacharyya et al., 2008}).

MNI in citrus maintained long-term productivity (^{Srivastava et al., 2012}). A meta-analysis of the rice-wheat system detected the increase in crop yields with MNI, by 2.5, 29.2 and 90.9% over FM, AOs and control, respectively (^{Sharma et al., 2019}). Another meta-analysis showed that FM + straw increases crop yields 5.1% more than FM alone (^{Xia et al., 2018}).

Integrated nutrition management and plant health

The quality of plant nutrition determines their histological and morphological characteristics, as well as their resistance and ability to suppress pathogens (^{Gupta et al., 2017}), but the excessive and unbalanced application of FMs makes plants more susceptible to diseases (^{Wu et al., 2015}). On the other hand, good plant health is favored with the existence in agroecosystems of microbial competition, hyperparasitism, antibiosis, acquired and induced systemic resistance in crops, inactivation of pathogen proliferation and influence of the physicochemical properties of AOs (^{Mehta et al., 2014}).

The MNI with balance of AOs and FMs has shown that it confers good conditions for DM, improves plant nutrition, ecosystem resilience and competition against pathogens (^{Sun et al., 2018}). However, such results do not always occur (^{Postma and Schilder, 2015}), this because the suppression of diseases depends on multiple and complex interactions of the soil components of different crops, management practices, fertilizers and environments (^{Sun et al., 2018}).

For example, a trial of late blight in tomato registered a lower incidence (13.8%) with 75% FM + Vc (4 t ha^-1) + biofertilizer compared to FM alone (31.6%) (^{Chatterjee and Khalko, 2013}). In chrysanthemum, ^{Pinto et al. (2013)} studied the effect of MNI with different AOs on Fusarium suppression and found that suppression was greater as the dose of Cp was increased, but adding biofertilizer, fish hydrolysate, chitosan or Trichoderma had no effect on the disease, the above suggests that suppression depends on the interaction of diverse chemical and microbiological factors.

In bananas, the level of suppression of Fusarium and CS had a negative correlation (r = -0.92, p< 0.01); 85.9% of the variance was explained by the supply of P and K (54.3%) and by the AM (31.6%). The supply of P and K was favored with high doses of MO (500 or 750 g plant^-1) + FM at 100 or 50%, while the AM was increased with 25% FM + MO. With 50% FM, even without MO, AM was stimulated, but with 100% FM without application of MO, the incidence of the disease increased (^{Sun et al., 2018}).

Integrated nutrition management and quality of agricultural products

Nutrition management affects the quality of crops. A study in wheat recorded that with MNI, in plants the content of N, Ca and Mg was doubled and the P quadrupled (^{García-Medívil et al., 2014}), in addition, in another study, the increase of protein in grain was recorded (^{Singh et al., 2017}). In tomato cultivation, AOs without FM generated less N in leaves and fruits, while with MNI, good quality fruits were obtained in terms of size, firmness, soluble solids, titratable acidity, macro and micronutrients (^{Hernández et al., 2014}), in other research with MNI of tomato, lycopene (35. 5%), antioxidant activity (24 to 63%), defense enzymes (11 to 54%) and vitamin C were also increased (^{Ilupeju et al., 2015}; ^{Verma et al., 2015}).

In the cultivation of chili (Capsicum spp.), capsaicin and ascorbic acid in fruits increased with the application of 75% N of neem cake + 25% N of urea, but with 25% N of EG + 75% N of urea, capsaicin levels decreased (^{Pariari and Khan, 2013}). In chili cultivation, the application of Vc alone or with FM increased acidity, protein, carotenes, lycopenes and vitamin C in fruits, but Ca was higher with the control than with MNI (Das et al., 2016b; ^{Premamali et al., 2019}).

The MNI of mustard (Brassica campestris) augmented the content of chlorophyll, sugar and proline (^{Mondal et al., 2017}), this was thanks to the improvement of chlorophyll biosynthesis and photosynthesis, this was due to the fact that MNI with Vc and Azotobacter increased the fixation and availability of N, the production of plant growth promoting substances and the absorption of nutrients (^{Singh et al., 2014}). In the cultivation of gladiolus (Gladiolus grandiflorus), the use of Vc + Cp inoculated with Trichoderma + 25% FM improved the shoot time, planting period, number and weight of corms, length of spikes and rachis, number of spikes and florets (^{Akter et al., 2017}).

With the MNI in basil (Ocimum basilicum), the oil yield (methyl chavicol and linalool) increased, compared to the AOs or with the FM (^{Anwar et al., 2005}) and in the nopal cladode (Opuntia ficus-indica), the zinc and boron content increased, but that of Mn was higher with the FM (^{Santiago-Lorenzo et al., 2016}).

Integrated nutrition management and influence of C and N on the environment

Globally, COS reserves are depleted in agroecosystems (^{Lal, 2018}). Organic farming benefits the environment and human health but could exacerbate greenhouse gas (GEI) emissions through increased land occupation to compensate for declining yields (^{Smith et al., 2019}). On the other hand, inadequate agricultural application of N causes environmental and health problems (^{Liu et al., 2014b}). As an alternative to this problem, MNI improves soil C capture (CCS), mitigates GEI emissions (^{Hua et al., 2014}) and N losses to the environment (^{Ren et al., 2014}). However, the C of crop residues on the soil surface stimulates AM, so COS is transformed into CO₂ or CH₄ through aerobic and anaerobic respiration (^{Liu et al., 2014a}).

In contrast, burying straw increases CCS and N retention, thereby reducing GEI emissions and N losses (^{Yang et al., 2019}). This demonstrates the need for proper agronomic management. In a study in tomato, MNI (75% FM + 4 t ha^-1 Vc + biofertilizer) improved the efficiency of N use (^{Chatterjee et al., 2014}). MNI also decreased runoff water and leaching of NH₄ ⁺ and NO₃ ^- (^{Doan et al., 2015}), in addition, it favored the reproduction of beneficial microbes, COS and the fixation and use of N (^{Ojo et al., 2015}). In basil cultivation, CBM and NBM were higher in soils with MNI with Vc, compared to those of FM.

This is due to the residual effect of Vc on CCS, due to the high production of biomass, rhizodeposition of carbonaceous materials and detached tissue (^{Anwar et al., 2005}). In rice paddies, MNI with balance in the proportions of FMs and AOs improved CCS and C mineralization (MC), but the overuse of AOs or FMs produced the reverse effects (^{Shi et al., 2019}). In winter wheat-summer corn rotations, the FM (N and P) applied for nine years did not alter the labile C, soil microbiota, or MC; while the use of straw + FMs increased labile C, microbes related to phospholipids and MC (^{Li et al., 2018a}).

In wheat-soybean and wheat-corn rotations under MNI for nine years, soil CO and N had increases of between 14 and 37%, this thanks to the fact that the C and N of AOs are stored in recalcitrant fractions associated with soil minerals (^{Li et al., 2018b}). With 46 years of MNI in the maize-wheat system, CBM, RBS, MC and microbial ratio increased compared to FM (^{Kaur et al., 2019}). A meta-analysis focused on the MNI with the use of crop residues detected that with straw return, COS increased 14.9% and the absorption of N by the crops grew 10.9%, this thanks to the microbial immobilization of N.

In rice paddies, MNI reduced losses of N₂O (17.3%), N leaching (8.7%) and runoff (25.6%). However, in non-flooded crops, with the use of FM + straw, N₂O emissions (21.5%) and NH₃ emissions (17.0%) increased, this due to increased nitrification-denitrification and urease activity in the soil. Emissions of NH₃ and N₂O decreased as the straw/C ratio and soil clay content were higher; but globally, straw return increases losses of N-NH₃ (^{Xia et al., 2018}).

In corn-soybean-wheat systems, depending on nutritional management, CO₂ emission had the following trend: FM + pig manure > FM + corn straw > FM (^{Li et al., 2013}). Therefore, in order to achieve balance of the effects of MNI, the specific characteristics of the agroecosystems where it is applied must be considered (^{Liu et al., 2014a}).

Economic convenience of integrated nutrition management

Any agronomic technology that improves the soil will be attractive to farmers only if it is economically profitable. MNI has demonstrated this characteristic. For example, in wheat, MNI (6 t of Cp ha^-1 + 34.5 kg of N ha^-1) improved CS and generated US $8.44 for each US $1.00 of additional investment in AOs and FMs (^{Demelash et al., 2014}). In a long-term study in soybean-wheat rotations, in years 1 to 5 and 26 to 30 of cultivation, the benefit:cost ratio (B:C) for soybeans was higher with MNI than with FM alone, which showed that in the long run MNI is more profitable, while FM generated no profits or losses (^{Bhattacharyya et al., 2008}).

In rice-wheat and cotton-wheat, MNI maintained accumulated net benefits, B:C and competitive net returns (^{Qazi et al., 2009}) and after 41 years of MNI, the economic yield of rice increases 9.34% (^{Sharma et al., 2019}). In several crops, MNI has shown its economic effectiveness, as it raised the productivity and profitability of wheat (^{Singh et al., 2017}), generated the highest net return, with a B:C of 1:3.5 in the cultivation of onion (Allium cepa) (^{Jamir et al., 2013}), while in tomato, it maximized the B:C (2.26 to 2.78) (^{Abedin et al., 2018}). However, in corn, in the short term (2 years), 100% FM generated higher net profit than MNI (with 50% FM) and the highest B:C occurred with the control (without FMs and without AOs) (^{Hashim et al., 2015}).

Conclusions

MNI is useful for sustainable agricultural management in several areas: a) it improves the quality of soil, water, air and biodiversity, in addition, it helps to mitigate global warming, this provided that practices are implemented to capture CO₂ derived from the increase in biological activity; b) it raises the quality of food and benefits the health of consumers and c) it maintains competitive yields and raises the economic efficiency of agroecosystems. Multiple studies agree that MNI can decrease FM by 25 to 50%, without affecting yields, with the improvement of the quality of agricultural products and the environment.

However, the benefits of MNI generally occur in the long term and depend on the doses, properties, times and methods of application of organic fertilizers and mineral fertilizers, as well as interactions with the components of the cultivation soil, management and environment. Therefore, the conditions of each agroecosystem and its environment should be considered to implement nutrition practices that lead to sustainability.