Long-term Effects of Fertilizers and Manure on Productivity of Soybean (Glycene max L.) - Safflower (Carthamus tinctorius) Cropping System and Soil Health under Vertisols in Central Platue of India

Soybean (Glycene max L.)-Safflower (Carthamus tinctorius) is the important oil seed crops in Maharshtra. Soybean occupies 49.10 lakh/ha area, 4.167 lakh/ha production and 317 kg/ha productivity (Annonymous, 2023). Similarly, safflower occupies 510 lakh/ha area, 0.111 lakh/ha production and 218 kg/ha productivity in Maharashtra. The production of soybean and safflower has increased remarkably with the development of high-yielding and fertilizer responsive crop varieties (Ladha et al., 2003; Manna et al., 2005). The stagnation and declining trends in yields in different crops and cropping systems have been reported to be mainly due to over-exploitation and mismanagement of soils, imbalanced use of fertilizers (Yadav et al., 2000; Neetu et al., 2025). Microorganisms present in soil play a key role in organic matter decomposition, nitrogen fixation, mobilization and solubalization of plant nutrients and also contribute to the efficiency of applied fertilizers (Poll et al., 2003). Soil biological properties respond rapidly and are influenced by the application of fertilizers, manures, irrigation, pest control measures, etc. Enzyme activities in soil showed positive correlations with microbial respiration, microbial biomass and soil management practices that alter microbial communities in soil are also expected to bring change in soil enzyme levels (Drjber et al., 2000; Nannipieri et al., 1990; Aon et al., 2001; Masto et al., 2007; Trasar-Cepeda  et al., 2008). However, Some researchers have noted beneficial effects of application of manure on the biochemical activity in soil due to associated effects on microorganisms (Jenkinson 1990; Kandeler et al., 1999), whereas, others reported harmful effects, which depend on quality of manure (Schipper and Sparling, 2000). Similarly, fertilizers have been reported to inhibit enzyme synthesis in soil (Olander and Vitousek, 2000) due to presence of readily available inorganic nutrients, while others indicated an increase in soil enzyme activities due to accelerated plant growth and secretion of enzymes by roots. Thus, it appears important to understand the dynamics and status of soil biological and biochemical properties for cycling of nutrients and assessment of soil health under different ecological settings, soil and crop management practices. Long-term experiments are valuable for providing information on the effects of continuous use of nutrient management options in crop production on the productivity and quality of soil. Soil biological and biochemical properties are considered reliable indicators of soil quality as these are highly sensitive to alteration of land management practices (Gil-Sotres  et al., 2005). Some long-term effects of integrated use of fertilizers and manure on yields and soil biological properties have been studied in different cropping systems under varying climatic conditions in India, this information is lacking behind under Vertisols in soybean-safflower cropping in central pleatue of India. Therefore, the present investigation was undertaken to diagnose the effects of long-term application of varying levels of fertilizers and manure on productivity and dynamics of soil microbial biomass and enzyme activities under soybean- safflower cropping system in Vertisols at Parbhani, Central India.

The long-term fertilizer experiment was initiated in 2006 at research farm of AICRP on Long Term Fertilizer Experiments, Department of Soil Science, Vasantrao Naik Marathwada Krishi Vidyapeeth, Parbhani, India with a Soybean (Glycene max L.) - Safflower (Carthamus tinctorius) cropping sequence. The soil of the experimental field comes under Vertisols with montmorillonitic, hyperthermic family of Typic Haplustert clayey in texture. The soybean cultivar MAUS-162 and safflower PBNS-12 were sown in 2019-20, 2020-21 and 2021-22 by adopting recommended crop management practice for both the crops in Kharif and Rabi seasons, respectively. The nutrients were applied through fertilizers (urea, single super phosphate, muriate of potash and diammonium phosphate). Zinc was applied through ZnSO₄. 5H₂O and FYM was applied every year before 15 days of sowing in Kharif season. The recommended dose of fertilizer (RDF) applied to soybean and safflower was 30:60:30 and 60:40:00 kg N, P₂O₅ and K₂O ha^-1, respectively. The mean annual rainfall is about 850 mm, received between June and September. The treatment combinations being used for soybean and safflower crops were  50% NPK (T1), 100% NPK (T₂), 150% NPK (T₃), 100% NPK+Hand weeding (T₄), 100% NPK+Zn (T₅), 100% NP (T₆), 100% N (T₇), 100% NPK+FYM (T₈), 100% NPK-S (T₉), FYM @ 10 ha^-1 (T₁₀) and Control (T₁₁). The Experiment was laid out in a randomized block design in a plot of 13.5 m x 10 m size with four replications. Soil samples were collected from individual plots after the harvesting of soybean and safflower during three years of experimentations at 0-15 cm soil layer. The population of bacteria, fungi and actinomycetes in soil was determined by serial dilution pour plate method using Nutrient agar medium for bacteria, Ken Knight and Munaier’s medium for actinomycetes and Martin’s Rose-Bengal streptomycin agar medium for fungi (Wollum, 1982). Microbial biomass carbon estimated by fumigation-extraction procedure as described by Jenkinson and Powlson (1976), soil organic carbon estimated by using oxidation and reduction procedure as given by Walkley and Black (1934), Soil de-hydrogenase by Tabatabai (1994) and  acid and alkaline  enzyme activities by Tabatabai and Bremner (1969). All the estimated soil biological properties were calculated based on oven dry weight of soil. The data on different parameters were analyzed statistically by adopting Fisher’s method of ANOVA suggested by Gomez and Gomez (1984).

Grain yields of soybean and safflower
 
After the 17^th years of crop cycle, the impact of fertilizers and manure on mean grain yields of soybean and safflower crops were monitored in soybean- safflower cropping system under Vertisols. Pooled data on grain yields of soybean and safflower tabulated in (Table 1) showed  significantly highest in treatment 100% NPK+5 t FYM ha”1and produced  higher mean grain yields of 9.37 per cent of soybean and 11.22 per cent of safflower over treatment 100% NPK, respectively and found significantly superior to all other treatments. Results indicated that the application of 100% N alone had increased the grain yield by 18.81 per cent of soybean and 24.01 per cent of safflower respectively, over control. Treatment 100% NP enhanced the grain yield of soybean and safflower by 107.59 per cent and 99.73 per cent respectively over the treatment 100% N. Further, the deficiency of S noticed itself through yield reduction of 3.15 per cent and 2.85 per cent in grain yields of soybean and safflower, respectively over treatment 100% NPK. Increase in yield might be due to beneficial effects of FYM on nutrient availability. Shirale et al., (2014) and Arbad et al., (2011) have also reported similar results. Further, Meshram et al., (2016) showed that the yield by NPK with FYM application could be attributed to enhanced population of phosphate solubilizing microorganisms. Treatment 100% NPK+Zn produced highest soybean and safflower mean grain yield increased by 3.98% and 5.70% over treatment 100% NPK, respectively. The significant positive response of Zn application with 100% NPK could be attributed to the development of Zn deficiency in soil due to continuous soybean-safflower  crops over the last 17^th years, as reported by Narendra et al., (2024); Meshram et al.  (2016). Treatments 100% NPK+HW and 100% NPK+Zn were statistically comparable with each other in grain yields of soybean and safflower. 


 
Microbial population
 
Treatment 100% NPK+5 t FYM ha^-1 recorded (Table 2) highest population of bacteria (57.75 cfux10⁶ g^-1) and actinomycetes (49.79 cfux10⁵ g^-1) after harvest of crops, respectively. However, fungal population was observed significantly highest in treatment FYM @ 10 t ha^-1 (13.62 cfux10^-4). Treatments 50% NPK, 100% N, 100% NP and 100% NPK-S recorded significantly lower population of bacteria, fungi and actinomycetes in soil than treatment  100% NPK. Khandare et al., (2020) and Tejada et al., (2009) reported depletion in native pools of plant nutrients in soil under these treatments, which caused reduction in plant biomass production (carbon substrate) and addition in soil (Suresh  et al.,1999). Treatment 150% NPK was comparable to treatment 100% NPK in soil microbial population and suggested that supply of inorganic nutrients higher than at optimum level without manure cannot support microbial population in soil (Selvi et al., 2004; and Ingle et al., 2014). The treatments of 100% NPK+Hand weeding, 100% NPK+Zn were statistically comparable with 100% NPK in recording mean counts of bacteria, fungi and actinomycetes after soybean  and safflower; however, these treatments gave significantly lower counts than 100% NPK+5t FYM ha^-1 indicating that manure has greater positive effect on microbial population in soil. The lowest microbial population was observed in control and 100% N treatment due to unavailability of organic sources.


 
Microbial biomass C and organic C in soil
 
It is evident from (Table 2) significantly maximum microbial biomass C and soil organic carbon were observed in treatment 100% NPK+5 t FYM ha^-1 (361.62 μg g^-1soil, 6.99 g kg^-1)  and significantly at par with 150% NPK (339.50 μg g^-1 soil 6.71 g kg^-1), this may be attributed to FYM as a food material for stimulating microbial growth, resulting in higher microbial biomass C and soil organic carbon. Patil and Puranik (2001) reported the beneficial effects of integrated use of fertilizers with FYM. However, application of FYM ensured the balanced supply of nutrients and carbon, which in-turn might have supported the higher population of microorganisms in soil (Basak et al., 2012; Lal 2021). Treatment 100%NPK and 150% NPK were comparable in microbial biomass C and organic C and lowest was observed in treatment 50% NPK. Similarly, continuous use of 100% N, 100% NP and 100% NPK (-S) resulted in significantly lower soil microbial biomass C and organic C than 100% NPK possibly due inadequate and imbalanced supply of nutrients for microbial utilization in soil.
 
Enzyme activity
 
The enzyme activities were monitored for good biological health indicator of soil and represent the overall metabolic status and have been widely used as an index of microbial activity. Treatment 100% NPK+5t FYM ha^-1 gave significantly maximum dehydrogenase (145.05 ug TPF g^-1 soil 24 hr^-1), acid (62.98 μg PNP g^-1 h^-1) and alkaline phosphatase enzyme (65.58 μg PNP g^-1 h^-1) activity in soil and was found significantly superior to all other treatments (Fig 1). A relatively more pronounced effect of FYM on soil enzyme activities in comparison to fertilizers has also been reported earlier and these results are in conformity with the findings of Bhattacharyya et al., (2008), who reported a four times increase in dehydrogenase activity in soil due to application of FYM in combination with NPK. Imbalanced and inadequate application of fertilizers in treatments 50% NPK, 100% NP and 100% N resulted significant decrease in dehydrogenase, acid and alkaline phosphatase enzyme activities. Simillarly, dehydrogenase, acid and alkaline phosphatase enzyme activities were significantly low in treatment 100% N as compared to all other treatments, which can be attributed to the presence of nitrate and nitrite that serve as alternative electron acceptors reported by Kukreja et al., (1991). The significantly lower enzyme activity in soil was observed in 100% NPK-S treatment in comparison to 100% NPK Treatments of 100% NPK and 150% NPK were at par and gave significantly higher acid phosphatase activity, by 41.9% and 50.5% and alkaline phosphatase activity, by 38.5% and 51.3%, increased over 50% NPK treatment for soybean and safflower, respectively.

The present study revealed that treatment 100% NPK+ FYM @5 t ha”1 gave higher yield of soybean-safflower cropping system in Vertisols. This treatment also recorded significantly maximum population of microorganisms, microbial biomass carbon, organic carbon and activities of various enzymes in soil, which play a vital role in nutrient cycling. It can thus be concluded that integrated use of fertilizers with FYM enhanced soil properties and sustaining productivity of soybean and safflower cropping system in Vertisols.

The present study was supported by ICAR-AICRP on Long Term Fertilizer Experiments, Department of Soil Science, Vasantrao Naik Marathwada Krishi Vidyapeeth, Parbhani ( MS).
 
Disclaimers
 
The conclusions were drawn from Long Term Fertilizer experiment and expressed in this research article are solely those of authors and do not necessarily represent the views of their affiliated institutions. The authors are responsible for the accuracy and completeness of information provided, but do not accept any liability for any direct or indirect losses resulting from the use of this content.
 
Informed consent
 
All procedures for determination of Soil available nutrients, microbial population and enzyme activities of these experiments were formulated and approved by the Committee, Annual Research Council of Vasantrao Naik Marathwada Krishi Vidyapeeth, Parbhani.

The authors declare that there are no conflicts of interest regarding the publication of this article. No funding or sponsorship influenced the design of the study, data collection, analysis, decision to publish, or preparation of manuscript.