Soybean (Glycine max) grown during the monsoon season is commonly infested by a diverse range of weeds including grasses, sedges and broad-leaf weeds, because of favorable temperature and moisture conditions. The annual grass weeds viz., Echinochloa colona, Echinochloa crusgalli, Cyperus rotundus, Cynodon dactylon, Cyperus iria and dicot weeds like Phyllanathus niruri, Euphorbia spp., Commelina benghalensis, Eclipta alba and Corchorus acutangulus etc. compete with the crop (Sharma and Shrivastava, 2002).
       
A balanced nutrient supply is essential for achieving optimal growth as well as yield and quality of crops. When nutrient levels drop below critical thresholds, plant metabolic processes are adversely affected, which in turn reduces the protein and oil production in crops such as soybean (Dwivedi et al., 2007). Therefore, integration of chemical fertilizers with farmyard manure (FYM) can improve yield-related traits, increase soybean yield and enhance nutrient content and uptake, ultimately leading to greater productivity in soybean cultivation.
       
Weeds significantly limit crop productivity by competing for resources such as nutrients, water and light. The composition, density and biomass of weed flora are influenced by several factors including crop type, land conditions, cropping pattern, irrigation practices, soil characteristics and weed management strategies. Nutrients availability play a crucial role in shaping weed dynamics and consequently, crop yield. Even with fertilizer application, crop yields may decline due to intense weed competition, as weeds often absorb nutrients more efficiently. The extent of yield loss depends on weed species, population density and soil nutrient status. Studies have shown that soil nutrient content strongly affects weed population, diversity indices and community structure (Neve et al., 2009). Furthermore fertilization induced challenges in soil nutrients can alter weed diversity and community succession, thereby influencing crop biomass and yield (Tarek, 2008).
         
Fertilizer application is a common agronomic practice used to enhance soil fertility and improve crop productivity. It influences weed growth both directly, by increasing nutrient availability and indirectly, by intensifying competition for resources, thereby shaping weed community dynamics. Balanced fertilization, particularly with optimal levels of nitrogen (N), phosphorus (P) and potassium (K), promotes vigorous crop growth and results in dense plant stands that restrict light availability to weeds, ultimately affecting their diversity. Increased competition for light is a major factor contributing to weed suppression and improved crop yield (Yin et al., 2006). Soil nutrient status also plays a significant role in determining weed density, diversity and community composition. Effective nutrient management can reduce weed infestation and alter species distribution. Moreover, the combined use of inorganic fertilizers and organic manures has been shown to modify weed flora, as reported in long-term studies involving NPK and FYM applications (Hossain et al., 2009).
       
Long-term nutrient management experiments are valuable for addressing recurring challenges in nutrient management and for optimizing crop productivity. These studies provide important insights for developing and refining management strategies. In situations where herbicide use is minimal or absent, weed dynamics-especially in alternative cropping systems-are influenced by the prolonged interaction of several factors, including crop rotations (Smith and Gross, 2006; Anderson, 2015), tillage practices (Armengot et al., 2016) and variations in nutrient sources and application rates (Little et al., 2021). Additionally, short-term cultural and mechanical weed control practices also contribute to these dynamics (Liebman et al., 1997). Therefore, a comprehensive understanding of the interactions among these factors is crucial for developing sustainable nutrient and weed management strategies, particularly in systems with limited reliance on herbicides. The present study was undertaken to evaluate weed density, species composition and weed seed bank as influenced by organic, inorganic and integrated nutrient management practices over a long-term period.

The long-term fertilizer field experiment was initiated in 2006-07 at Long-term Fertilizer Experiment Research, VNMKV, Parbhani, Maharashtra, India. The experiment has been laid out in randomized block design with 10 treatments replicated thrice. This study on weed dynamics and weed seed bank was carried out during kharif season 2023 and 2024. The treatments comprised T₁ - 50% NPK, T₂ - 100%NPK, T₃ - 150% NPK, T₄ - 100% NPK+25 kg ZnSO₄ ha^-1, T₅ - 100% NP, T₆ - 100% N,T₇ - 100% NPK+FYM@ 5 tonnes ha^-1, T₈ - 100% NPK-Sulphur, T₉ - Only FYM@ 10 tonnes ha^-1 and T₁₀- Absolute control. The soil of the experimental site was Vertisol (montmorillonitic). The site of experiment was located at 76°46' E longitude and 19°16' N latitude with an elevation of 408.46 m above the mean sea level. Fertilizers were applied to the soil on the day of sowing of seeds as per treatment except to the control treatment. The sources of nutrients were fertilizers (urea, single super phosphate, muriate of potash, diammonium phosphate, Zinc sulphate) and FYM was applied 15 days prior to the sowing for soybean crop in kharif. The recommended dose of fertilizer (RDF) was 30:60:30 kg NPK per hectare. The plot size was 13.5 m × 10 m , soybean variety MAUS-162 was sown at a spacing of 45 cm × 5 cm. Weed seed distribution in the soil was studied at different depths through pot culture experiments before sowing of soybean during 2023 and 2024. Soil samples were collected from the experimental site after the harvest of previous Rabi crop in sequence. The soil samples were taken at 0-5 cm and 5-10 cm dried under shade. One kg of soil from each depth was weighed and kept in plastic pots containing holes at the bottom side to study the emerging weeds present in the soil. The pots were watered manually as and when needed to maintain adequate moisture. After germination, the weed seedlings were identified, counted and removed and again soil was thoroughly stirred and watered regularly for another flush of weeds. The cycle of operation was repeated till all the weed seeds were exhausted. Weed counts (number 0.25 m^-2) were recorded at different stages from two spots per plot. These weeds were categorized as monocot and dicot weeds and expressed as number m^-2 and averaged over two random spots per plot. After sorting as monocot and dicot weeds, these categories of weeds were dried in hot air oven at 60°C,till constant dry weight was recorded. The dry weight of weeds as expressed separately for monocot and dicot weeds as g m^-2 at different stages. The available nitrogen content was determined using the alkaline potassium permanganate method, following the procedure described by Subbiah and Asija (1956). Available phosphorus was measured from the soil using 0.5M Sodium bicarbonate, employing Olsen’s method as outlined by Jackson (1967). Available potassium measured using neutral normal ammonium acetate (NH4OAc) and the potassium content in the extract was determined using a Flame Photometer, following the method described by Piper (1966). The soybean plants from each net plot were threshed and seeds were cleaned. The cleaned seeds obtained from each plot were weighted and expressed as seed yield of soybean in kg ha^-1. The experimental data collected on plant growth parameters and yield components of soybean were subjected to Fisher’s method of “Analysis of Variance” (ANOVA) as outlined by (Panse and Sukhatme, 1954).

The data related to the seed and straw yield of soybean, weed dry weight at different stages and weed seed bank as influenced by long term nutrient management treatments during the course of investigation were critically interpreted and results are presented below.
       
The dominant monocot and dicot weeds associated with soybean during experimentation were Brachiaria erucifrmis, Cyperus rotundus among monocots and Phyllanthus niruri, Acalypha indica, Ipomoea maxima, Euphorbia geniculata, Euphorbia microphylla among dicots.
 
Seed yield and straw yield of soybean as influenced by different treatments
 
Seed yield (Kg ha^-1)
 
The data on seed yield (kg ha^-1) of soybean showed significant differences among the treatments due to the long-term nutrient management.
       
Significantly higher seed yield (2518, 2442 and 2480 kg ha^-1) was recorded with the treatment receiving 100%NPK+FYM which was on par with the treatments receiving 150% NPK (2333, 2398 and 2366 kg ha^-1), 100%NPK + Zn (2259, 2348 and 2304 kg ha^-1) and 100% NPK (2258, 2334 and 2297 kg ha^-1). While, the lowest seed yield was recorded with the control (898, 944 and 921 kg ha^-1) and 100% N (1037, 1044 and 1041 kg ha^-1) during 2023, 2024 and pooled analysis.
       
The increased seed yield observed under the combined application of inorganic fertilizers and organic sources may be attributed to a sustained supply of nutrients and more efficient utilization of applied inputs. This improvement can be linked to enhanced microbial activity, which plays a key role in nutrient transformation and fixation processes. Comparable results have also been reported by Arbad and Ismail (2011) and Ravankar et al. (1995). In contrast, the reduced yield recorded under the application of 100% nitrogen alone may be associated with increased soil acidity and the gradual deterioration of soil quality resulting from the continuous use of nitrogen over several years (Dutta et al., 2013). Khandare et al. (2026) also reported higher soybean and safflower yields with application of 100% NPK+5 t FYM ha^-1 along with maximum and significantly more population of bacteria, fungi, actinomycetes and soil microbial biomass C.
 
Straw yield (kg ha^-1)
 
Analysis of the data presented in Table 1 revealed that straw yield differed significantly among the various nutrient management practices. The highest straw yield (3526, 3131 and 3329 kg ha^-1) was obtained with the application of 100% NPK in combination with FYM, which proved superior to the other treatments during 2023. However, in 2024 and based on pooled mean data, this treatment remained statistically comparable with 150% NPK, followed by 100% NPK + Zn and 100% NPK. The lowest straw yield was observed under the control treatment, followed by the application of 100% nitrogen alone.


 
Weed studies
 
Data related to the weed seed bank and the dry weight of weeds at different growth stages during 2023 and 2024, as influenced by various treatments, are presented in Table 2 to 5.








 
Weed seed bank studies
 
Weed seed bank at 0-5 cm soil depth (no.kg^-1 soil)
 
At the 0-5 cm soil depth, the number of monocot weed seeds varied significantly across treatments. The highest monocot seed count was recorded under 100% NPK + Zn (2.96 and 3.06 kg^-1 soil), followed by FYM @ 10 t ha^-1 (T₉) (2.33 and 2.64 kg^-1 soil), 100% NPK - S (T₈) (2.00 and 2.28 kg^-1 soil) and 150% NPK. In contrast, the lowest number of monocot weed seeds was observed in the control treatment and in plots receiving 100% nitrogen alone (T₆), followed by 50% NPK during both years of the study.
       
A significantly higher number of dicot weed seeds was also recorded under 100% NPK + Zn, followed by FYM @ 10 t ha^-1 and 100% NP. The lowest dicot seed population was found in the 50% NPK treatment. Similarly, the total weed seed bank was highest under 100% NPK + Zn, followed by FYM @ 10 t ha^-1 and 100% NP, whereas the minimum number of weed seeds was recorded in plots receiving 50% NPK.
 
Weed seed bank at 5 -10 cm soil depth (No. kg^-1  soil)
 
At soil depth of 5-10 cm depth overall number of weed seeds was lower as compared to 0-5 cm depth. Among the treatments significantly higher number of monocot, dicot and total weed seeds were observed under 100%NPK +Zn (6.2 and 6.84 kg^-1 of soil) followed by FYM @10 t/ha during first and second year of study respectively. Significantly lower number of monocot weed seeds was noticed in 50% NPK and 100% N and absolute control treatments.
       
From this study, it was observed that, the abundance of weed seeds decreased with increase in soil depth irrespective of the nutrient management treatments, similar o he observations made by (Kelton et al., 2011). There excised substantial variations in soil nutrient contents among different treatments and substantial temporal changes in nutrient conditions under each treatment. Thus, weed species with a narrow nutrient niche are likely to be eliminated gradually. In addition, fertilization treatments might have also affected the competition between weed and crop (Yin et al., 2006).
       
Total weed seeds were higher in 100%NPK +Zn followed by FYM @10 t/ha during first and second year of experimentation respectively. Significantly lesser number of monocot weeds was observed in 50% NPK and absolute control.
 
Dry weight of weeds (gm^-2 )
 
The data on weed dry weight at different growth stages of soybean are presented in Table 4 and 5.
 
Dry weight of weeds at 15 DAS
 
From the data (Table 5), it was observed that at 15 DAS there were no significant difference with respect to weed dry weight of dicot weeds during first year of study while during second year significantly higher weed dry matter was observed in treatment FYM@10t/ha and 100%NPK+FYM@ 5 t/ha while, lower dry weigh of broad leaf weeds was recorded in control. Regarding data on dry weight of monocot weeds was significantly higher in 100% NP which was on par with 150% NPK while, lower dry weight of monocot weeds was recorded in100% N. With respect to the total weed dry weight FYM @10 t/ha (T₉) recorded higher weed dry weight (4.34 gm^-2) and it was at par with 100% NPK+FYM@ 5 t/ha, 100% NP (3.48 gm^-2) and 150% NPK (2.68 gm^-2). The results of present study were observed to be in line with the findings of Khatri et al. (2020) who reported that application of FYM @ 10 t ha^-1 followed by recommended fertilizer dose recorded higher weed density and dry weed weight compared to any of N, P₂O₅ and K₂O or all nutrient omitted treatments. While the control treatment recorded a lower weed dry weight (0.51g m^-2).
 
Dry weight of weeds at 30 DAS
 
Significantly higher dry weight of dicot weeds was recorded in treatment 100% NPK + Zn (T₄) and it was at par with 100% NP (T₅) and FYM @10 t/ha (T₉) at 30 DAS during first and second year of study (Table 5). While, lower dicot weed dry weight was recorded in 50% NP (0.5 g m^-2). For monocot weeds, the effect of treatments was observed to be non significant during first year and during second year FYM @10t/ha recorded highest dry weigh of monocot weeds.
       
Treatment 100%NPK + Zn (T₄) recorded higher total weed dry weight and it was at par with FYM @10 t/ha (4.34 and 3.41 g m^-2) and 150% NPK, while 50% NPK and control recorded lower weed dry weight. Higher weed dry matter under treatments with FYM application could be attributed to the increased availability of nutrients in a balanced form and improved physio-chemical properties of the soil (Table 6). Significantly lower dry matter accumulation by weeds was recorded under the treatment with no fertilizer application. The application of manure in cropping systems increases weed density and biomass (Kaur and Kaur, 2018). The use of both organic and inorganic fertilizers in agro-systems not only benefits the crop but also weeds, whose nutrient uptake system is more efficient than that of crop plants (Hunkova et al., 2011). Application of 100% organics (100% Rec. N through different organic sources each equivalent to 1/3 of Rec. N i.e. FYM+ vermicompost + non edible oil cake) + VAM produced significantly higher crop yield coupled with organically weed management practice i.e. weed free and application of rice bran @ 4 t ha^-1 which not only were economically viable and efficient organic weed management options but also kept dominant weeds below threshold level (Sharma et al., 2023). 

Based on the two years findings and pooled results, it can be concluded that, application of 100% NPK+FYM @5 t ha^-1 was found productive recording the highest seed yield (2518, 2442 and 2480 kg ha^-1) and straw yield (3526, 3131 and 3329 kg ha^-1) in soybean was followed by application of 150% NPK, while minimum seed yield was recorded with control followed by application of 100% N. The weed seed density decreased with increase in soil depth in all the nutrient management treatments. The total weed dry weight was higher with sole application of FYM @10 t/ha, 100% NP and 150% NPK while, lower weed dry weight was recorded in100% N, 50% NPK and absolute control.

The present study carried out at research centre on Long-term Fertilizer Experiment Research, VNMKV, Parbhani along with the necessary facilities.
 
Disclaimers
 
The views and conclusions expressed in this article are solely those of the authors and do not necessarily represent the views of their affiliated institutions. The authors are responsible for the accuracy and completeness of the information provided, but do not accept any liability for any direct or indirect losses resulting from the use of this content.

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 the manuscript.