Impact of cropping intensity on soil nitrogen and phosphorus for sustainable agricultural management

1 Introduction

The intensification of agriculture and increased cropping intensity are critical for boosting production. Cropping intensity, defined as the number of crops grown annually in a given area (Biradar and Xiao, 2011). It affects nutrient demand, cycling, and distribution in the soil, influencing nutrient needs and dynamics throughout the crop cycle. Intensification alters nutrient availability, including nitrogen and phosphorus that are crucial for growth and development of plants (Grant et al., 2002). Nitrogen is a fundamental component of all proteins and protoplasm and is crucial for soil fertility. Organic nitrogen constitutes 94.2 % of total nitrogen, with the remainder as mineral nitrogen (Nayak et al., 2013). Plants primarily uptake NH₄⁺ and NO₃^– ions, favouring the latter when the former is abundant. Moreover, the mineralization of the organic nitrogen fraction plays a substantial role in supplying nitrogen to plants. On the other hand, phosphorus in soil primarily exists as the orthophosphate anion, which is less mobile macronutrient. However, it is essential for genetic information and energy transfer in cells. Unfertilized soils have very low phosphorus levels, less than 0.1 parts per million (ppm) phosphorus. Soil phosphorus fractions vary in mobility, bioavailability, and can change under specific conditions (Sharpley and Moyer, 2000). In the current era, our emphasis is on ensuring global food security despite rapidly diminishing cultivated land. The goal is to intensify cropping while maintaining soil health and sustainability. However, excessive intensification may harm soil fertility (Lafond et al., 2011). Incorporating legumes and organic amendments can enhance nutrient availability through plant mediated C input, intensity of cultivation and maintain long-term productivity under a diversified cropping system. Therefore, in present era farmers can move towards intensive cropping but only by practicing diversification of cropping systems. We hypothesized that increasing legume based cropping system diversity would help enhance soil nutrients, biological nitrogen fixation and their impact on long-term agricultural output requirements. To examine this hypothesis, our objective was to identify cropping systems that maximize productivity and resource efficiency while also maintaining high levels of nitrogen pools and organic phosphorus fractions in the soil.

2 Materials and Methods

3 Results

3.1

3.1 Mineralizable nitrogen

The mean value of available nitrogen ranged from 249.26 kg ha⁻¹ to 287.46 kg ha⁻¹ in 0–5 cm depth. The highest values were recorded in T₅ while the lowest values were recorded in T₁ whereas, T₂, T₃ and T₄ were statistically at par with T₅.The available soil nitrogen values declined with increasing depths (Fig. 1a). The mean value of available soil nitrogen was highest (287.46 kg ha⁻¹) in 0–5 cm soil depth and lowest was recorded in 15–30 (195.97 kg ha⁻¹) cm depth. Under high intensity cropping, the available nitrogen content exhibited a significant increase in 0–5 cm depth. Further, no significant difference was observed in other soil depths.

Close

Fig. 1

Fig depicting effect of high intensity cropping on (a) Mineralizable Nitrogen and (b) Total Nitrogen (TN) at different depths.

Export to PPT

3.3

3.3 Nitrate nitrogen

The data presented in Fig. 2a showed that the mean value of nitrate nitrogen ranged between 22.96 mg kg⁻¹ to 29.58 mg kg⁻¹. The highest values were recorded in T₅ while the lowest values were recorded in T₁ whereas, T₂, T₃ and T₄ remained statistically at par with T₅ at 0–5 cm soil depth (Fig. 2a). The similar trend was observed in 5–15 cm and 15–30 cm depths. The nitrate nitrogen values decreased with increasing depths. The mean value of nitrate nitrogen was highest (29.58 mg kg⁻¹) in 0–5 cm depth and lowest values (19.49 mg kg⁻¹) were recorded in 15–30 cm depth. Nitrate nitrogen exhibited a significant increase due to high intensity cropping in 0–5 cm depth.

Close

Fig. 2

Fig depicting effect of high intensity cropping on (a) Nitrate Nitrogen (NN) and (b) Ammonical Nitrogen (AMN) at different depths.

Export to PPT

3.5

3.5 Soil microbial biomass nitrogen (SMBN)

A widely recognized biological indicator of alterations in soil management is SMBN, known for its remarkable sensitivity to changes in soil management practices. From the data given in Fig. 3a, it was concluded that the mean value of SMBN ranged between 19.94 μg g⁻¹ to 23.78 μg g⁻¹ in 0–5 cm soil depth. The highest values were recorded in T₅ while the lowest values were recorded in T₁. T₂ and T₄ were statistically at par with T₅. The similar trend was observed in 5–15 cm and 15–30 cm depth. The results showed that SMBN decreased with increasing depths. The mean value of SMBN was highest (23.78 μg g⁻¹) in 0–5 cm depth and lowest values (16.38 μg g⁻¹) were recorded in 15–30 cm depth. SMBN exhibited a significant increase due to high intensity cropping at 0–5 cm and 5–15 cm soil depth. However, no significant difference was observed in 15–30 cm soil depth.

Close

Fig. 3

Fig showing effect of high intensity cropping on (a) soil microbial biomass nitrogen (SMBN) and (b) available phosphorus at different depths.

Export to PPT

3.7

3.7 Labile organic phosphorus (LOP)

It was revealed that under 0–5 cm depth the amount of labile organic phosphorus ranged between 50.46 mg kg⁻¹ to 54.84 mg kg⁻¹(Fig. 4a). The highest values were recorded in T₂ while the lowest values were recorded in T₁. T₃, T₄ and T₅ were statistically at par with T₂ at 0–5 cm soil depth. The values of labile organic phosphorus showed a decrease with increasing depths. The mean value of labile organic phosphorus was highest in 0–5 cm depth and lowest values were recorded in 15–30 cm depth. At 5–15 cm and 15–30 cm soil depth, similar trend was noticed i.e T₂ had highest values of available phosphorus while T₁ exhibited the lowest values. Labile organic phosphorus (LOP) exhibited a significant increase due to high intensity cropping in 0–5 cm depth. However, no significant difference was observed in 5–15 cm and 15–30 cm soil depth.

Close

Fig. 4

Fig showing effect of high intensity cropping on (a) labile organic phosphorus (LOP) (mg kg⁻¹) and (b) moderately labile organic phosphorus (MLOP) (mg kg⁻¹) fractions of soil at different depths:

Export to PPT

3.9

3.9 Non-labile organic phosphorus (NLOP)

The non-labile organic phosphorus content among different treatments, ranged from 32.88 to 37.02 mg kg⁻¹. However, among different treatments, the maximum amount was observed in T₄ (37.02 mg kg⁻¹) followed by T₅ and lowest value was observed in T₁ (32.88 mg kg ^-1) (Fig. 5). It was also concluded that T₃ and T₅ were statistically at par with T₄. At 5–15 cm and 15–30 cm soil depth, similar trend was observed with T₄ exhibiting the highest and T₁ exhibiting the least value. The results further revealed that non– labile organic phosphorus in soil decreased with increasing depth. The effect of different treatments on non-labile organic phosphorus were found to be significant in 0–5 cm soil depth and non-significant at 5–15 cm and 15–30 cm soil depth respectively.

Close

Fig. 5

Fig representing the effect of high intensity cropping on non– labile organic phosphorus (NLOP) (mg kg⁻¹) fractions of soil at different depths.

Export to PPT

4 Discussions

Cropland ecosystems have a substantial impact on ecosystem functionality, sustainability, and resilience, primarily due to significant alterations in nitrogen pools. The mean values of mineralizable nitrogen were found to be highest in T₅ followed by T₄ while the lowest values were observed in T₁. Due to the consistent addition of organic manure, root biomass C and root exudates than other croplands (Sharma et al.,2009). The introduction of leguminous crops into cropping systems aids in atmospheric nitrogen fixation in the soil, potentially contributing to the elevated levels of mineralizable nitrogen into the soil. Porpavai et al. (2011), also stated that adding legume crops to the cropping system increased the nitrogen content of the soil. Ali et al. (2012) and Naresh et al. (2017) also reported similar results. Furthermore, the findings indicated a decline in mineralizable nitrogen content with increasing depths, possibly attributable to the diminished presence of soil organic carbon at greater depths.

Overall, the rise in total soil nitrogen compared to the initial levels was attributed to the increment in organic matter, root/plant carbon biomass, and enhanced carbon input resulting from high net primary production, predominantly from the root systems (Fu et al., (2019). The same happened in T₅ because of incorporation of two legumes which further increased the amount of soil total nitrogen. Continuous fertilizer application, either alone or combined with organic materials, may lead to the elevation of total nitrogen content in the course of time, possibly owing to the escalation of diverse organic and inorganic nitrogen fractions. Santhy et al. (1998), Huang et al. (2021) and Kumar et al. (2022) both documented comparable rises in the amount of total nitrogen levels after the addition of nitrogen from either organic or inorganic sources in various regions of the country.

The mean value of ammonical nitrogen was found to be highest in T₅ followed by T₄ while the lowest value was obtained in T₁ at 0–5 cm soil depth. The comparable pattern was observed at soil depths of 5–15 cm and 15–30 cm. This could be ascribed to the contribution of nitrogen from leguminous plants, residues and N fertilizer which further enhanced NH₄⁺-N concentration through mineralization of soil organic nitrogen. Fu et al. (2019) and Virk et al. (2022) reported that the continuous use of fertilizer and manure over the period of time may be the cause of the rise in NH₄⁺-N in the various treatments. This may be because cultivation accelerates the decomposition of organic matter and the organic-N that has been mineralized and have contributed to ammonical nitrogen pool in the soil. From the data, it was observed that maximum nitrate content was found in T₅ while the minimum content was found in T₁. This might be due to the increased microbial growth and activity and also due to higher soil organic matter content which further leads to hastening of mineralization and increase NO₃ content in T₅. The findings are in concurrence with Sainju and Lenssen (2011), Li et al. (2019) and Arunrat et al. (2022).

The maximum content of soil microbial biomass nitrogen was observed in T₅ while the minimum values were observed in T₁. The minimum values in T₁ were attributed because no FYM application and legumes in T₁. This may be because crop residues of legumes have been found to promote higher growth and activity of microbes. Chirinda et al. (2008) and Yan et al. (2022) also documented that cropping systems utilizing legumes had greater MBN and nitrification rates than systems that only used inputs from manure and mineral fertilizer. The stronger root development and more plant residues in fertilised plots might have boosted carbon content of the soil, resulting in higher microbial biomass carbon and nitrogen. Muhammad et al. (2021) also discovered higher MBN value in crop rotations with legumes. The values of SMBN decreased with increasing depth. The lowest values were obtained at 15–30 cm soil depth. It was noticed that the effect of cropping intensity was significant at 0–5 cm and 5–15 cm soil depth. The findings are consistent with those of Li et al. (2019), Muhammad et al. (2021) and Potter et al. (2022).

The mean values of available phosphorus ranged from 11.50 to 15.07 kg ha⁻¹ at all the three depths. This might be explained by the fact that crops in cropping systems absorb less phosphorus than the applied amount. The findings suggest that when organic and inorganic fertilizers are applied together, it may not be essential to make large applications of phosphorus fertilizer to enhance the available phosphorus fractions in the soil. To avoid the irreversible adsorption of excess phosphorus, a high organic matter content can mask enough Al and Fe sorption sites, or it can change the surface charge of minerals to reduce the number of adsorption sites and raise the level of phosphorus in the soil solution (Siddique and Robinson, 2003). In order to prevent Fe, Al, Mg, and Ca from reacting with phosphate, hydroxyl acids and organic anions released during the breakdown of organic materials may complex or chelate them (Sharma et al.,2001). Deka and Singh (1984) reported that incorporating potatoes and radish to cropping systems reduced the amount of phosphorus that was easily available because of excessive phosphorus consumption and utilization. Also, the available phosphorus gradually decreased from the surface to the subsurface layer, with higher content observed in the surface layer because mobility of phosphorus was low in soils. Arya et al. (2016), Nunes et al. (2020) and Qaswar et al. (2022) also documented similar findings.

The mean value of labile organic phosphorus was found to be significantly higher in T₂ followed by T₃ whereas the lowest values were found in T₁. The LOP fraction of OM is small but essential to P cycling, sustaining microbial and enzymatic processes (Sharma et al., 2005). NaHCO₃-Po levels in T₁ might have decreased as a direct consequence of continuous cropping, without external input. Ahmed et al. (2020), Qaswar et al. (2022), Sharma et al. (2022) and Anil et al. (2022) also reported similar results. Moderately labile organic phosphorus was found to be significantly affected by the treatments of different cropping intensities at 0–5 cm and 5–15 cm soil depth. The maximum amount of MLOP was recorded in T₂ followed by T₃. The moderately labile P pool was thought to consist of the NaOH-Po portions (Halloran et al.,1987). This proportion was greater than the labile P fractions that could be extracted using NaHCO₃. Transformation of native soil phosphorus (P) from moderately labile and non-labile fractions to labile forms can occur due to substantial P extraction by plants (Delgado et al., 2002). The results exhibited that the values of non-labile organic phosphorus were found to be significantly influenced by different treatments. The highest values were found in T₄ followed by T₅. As chemical fertilizers were used more often, the amount of NLOP in the soil rose, suggesting that over prolonged periods of cropping, specific active soil phosphorus fractions were immobilized and more phosphorus underwent chemical fixation in the soil. T₄ had the highest fertilizer application and NLOP values. The substantial release of carbon dioxide (CO₂) at the time of organic matter decomposition may contribute to the elevation of phosphorus levels, leading to phosphorus fixation in alkaline soils, particularly in calcareous soils. These findings are corroborated by the research of Mao et al. (2015), Ahmed et al. (2020), Hussain et al. (2022) and Sharma et al. (2022).

5 Conclusion

The findings of the current study inferred that the high intensity cropping has significant effect on soil nitrogen pools and phosphorus fractions. Further, the study indicated that intensification of all the cropping systems through leguminous crops is responsible for higher nitrogen fixation and it enhanced the availability of various nitrogen pools with average increase of 2.02 % for mineralizable nitrogen, 1.72 % for total nitrogen, 14.76 % for ammonical nitrogen, 30.07 % for nitrate nitrogen and 41.84 % for soil microbial biomass nitrogen at 0–5 cm soil depth. The combined use of organic manures and fertilizers and their decomposition released organic acids and boost various phosphorus fractions. The continuous use of a variety of inorganic and organic soil amendments along with increased cropping intensity not only enhances the status of nitrogen pools and phosphorus accumulation but also hastens the process of mineralization in soils. In addressing the challenges of population growth and rising food demand in the developing world, a strategic revaluation of agricultural practices is imperative. With a projected surge of 9.8 billion individuals by 2050 and limited agricultural land per capita (0.29 ha), conventional methods fall short. To meet this demand sustainably, we must intensify cropping systems while preserving environmental integrity. Incorporating legumes into crop rotations and balancing organic and inorganic amendments enhances productivity while maintaining soil and ecosystem health. This synergistic approach not only enhance productivity but also fosters the overall health and resilience of soil and ecosystems. Therefore, farmers are advised to apply optimum P-fertilization adhering to the requirements of the crop to enhance the availability of organic phosphorus fractions under the high cropping intensities of the Chenab-Ravi basin.

CRediT authorship contribution statement

Tamanna Sharma: Data curation, Formal analysis, Methodology, Writing – original draft. Vivak M. Arya: . Vikas Sharma: Conceptualization, Project administration, Supervision, Visualization, Writing – review & editing. Sandeep Sharma: Data curation, Methodology, Software, Writing – review & editing. Simona M. Popescu: Formal analysis, Investigation, Validation, Visualization, Writing – review & editing. Nikhil Thakur: Data curation, Methodology, Visualization, Writing – review & editing. Jeelani M. Iqbal: Formal analysis, Software, Validation, Visualization. Mohamed A. El-Sheikh: Formal analysis, Validation, Visualization, Writing – review & editing. Gurjinder S. Baath: Formal analysis, Investigation, Software, Validation, Visualization.