Abbreviations:
ACP: acid phosphatase activity, ALP: alkaline phosphatase activity, AZO-Aztobacter counts, Na: available nitrogen, Pa: available phosphorus, Ka: available K, Sa: available sulphur, β-glu: β-glucosidase, BSR: basal soil respiration. CZ: central zone, DAP: diammoinum phosphate, DHA: dehydrogenase activity, EC: electrical conductivity, EZ: eastern zone, FDA: fluorescein diacetate hydrolytic activity, MBC: microbial biomass carbon, MBN: microbial biomass nitrogen, MDS: minimum data set, NI: Nutrient index, SOC: soil organic carbon, SQI: soil quality index,S : sensitivity index, TC: total carbon, TCA: total culturable actinomycetes counts, TCB: total culturable bacterial counts, TCF: total culturable fungal counts, TYE: targeted yield equations, WZ: western zone.
INTRODUCTION
India is the second largest sugarcane producer in the world with 18.7% of world’s production during 2017 after Brazil, which is the largest (37.0%) producer of the world (FAO, 2019). The increasing demand of foodstuffs, animal feed, chemicals and industry are the major causes of sugarcane expansion. Lisboa et al. (2011) stated that increasing demand of bio-ethanol is the key driver of this quick increase. Since, it used as a sustainable bio-energy sources, reduces emission of greenhouse gases (GHGs), minimize unpredictability related to volatility of fossil fuel prices (Black et al., 2012), and endowing a fixed income source for farmers. Thus, sugarcane paramount a key role in Indian economy as ⁓50 million farmers’ and 5.0 lakhs skilled and unskilled workers are engaged in its production and processing (Krishnakant et al., 2015).
In India, sugarcane cultivated ⁓ 45% and 55% of the total area in tropical and sub-tropical conditions, respectively but vice-versa in its production. Uttar Pradesh is the key sugarcane producing province under subtropics has largest area (2.234 m ha), production (177.06 m t) and average productivity (79.26 t ha-1) during 2017-18 (Cooperative sugar, 2021). As many as 30 district, in which Muzaffarnagar, Meerut, Bijnor, Moradabad and Saharanpur, districts in western zone (WZ), Bareilly, Shahjahanpur, Lakhimpur-Kheri and Sitapur districts in central zone (CZ) and Kushinagar, Gonda, Balrampur, Basti, Bahraich and Maharajganj in eastern zone (EZ) are considered as the main cane producing district of Uttar Pradesh. WZ is considered as cane heart land of the state due to highest cane production in India. Though, wide yield variations existed across the cane production zones of Uttar Pradesh despite having similar soil type (alluvial soils) might be due to variations in nutrient management and edaphic factor. Rahman and Bee (2019) observed 82.9, 72.0 and 66.9 Mg ha-1 and Cooperative sugar (2021) reported 90.7, 86.8 and 77.8 Mg ha-1 cane productivity of Muzaffarnagar, Lakhimpur-kheri, and Kushinagar district during 2016-2017 and 2019-20, respectively. Indeed, cane productivity has been increased significantly during the decade due to inducting high yielding variety and advance management practices, but yield variation remains is the cause of concern in sub-tropical region (Uperti and Singh, 2017). Yet, the right causes of cane yield variations are not confirmed. Albeit, there are various reasons including increasing compactness, degrading soil structure, nutrient losses through erosion, declining SOC, and increasing multi-nutrient deficiency (Hartemink, 1998). In addition, low-lying area affected with floods, surface runoff and water logging during monsoon can be a major cause to suffer production and productivity of sugarcane in EZ (Rahman and Bee, 2019). Imbalance fertilization over the years can be another factor for variations in cane yield, nutrient index and soil quality. Because, sugarcane is a heavy nutrient feeder crop required 150–350 kg N; 60–100 kg P2O5, and 60–120 kg K2O ha-1 annually depending upon planting time, growing condition and nutrient status in soil. However, sugarcane growers largely using 150:60:60 kg N, P2O5 and K2O ha-1 year-1across the sub-tropical zone from the decades despite changes of fertility gradient (from medium to low or very low categories of nutrients). Contrary to that, sugarcane removed about 208, 53 and 280 kg N, P, and K ha-1 year-1 for producing 100 Mg ha-1 cane yields (Shukla et al., 2017). Sugarcane mono-cropping over the years depleted 53, 56, 84 and 86% SOM, total N, Olsen P and exchangeable K, respectively than the virgin land (0-30 cm depth). Chi et al. (2017) also suggested that prolonged sugarcane cropping has detrimental effects on soil fertility, but deterioration depends on soil types, surface runoff and water logging (Satiro et al., 2017). Heavy mechanization in sugarcane also caused adverse impact on soil compaction notably in top soils. Consequently, reduce soil aeration, soil resistance and infiltration rates and increases runoff and soil erosion in Brazil (Macedo, 2007). Thus, cumulative effects of these factors affect microbial life in soils (i.e. bacterial, fungal, actinomycetes, and nematodes counts) (Hartemink, 2008). Holt & Mayer (1998) observed that long-term sugarcane cultivation had low enzymes’ activity than natural habitats and pasture. Although, it varied with management practices such as unfertilized/fertilized, burnt/green harvesting, trash removal/trash mulching and tillage level employed (Yadav et al., 2009; Stirling et al., 2010; Castioni et al., 2018).
Soil quality may be defined as the capacity of a soil to function within ecosystem boundaries to sustain biological productivity, maintain environmental quality, and promote plant and animal health (Doran and Parkin, 1994a). Recently, it utilized by various researchers as a tool for assessing the suitability of management practices implies in a soil, and indices have been developed to grade and compare soil conditions over time and or between different locations (Nortcliff, 2002). Various methods such as soil management assessment framework (Masto et al., 2007) , Fuzzy association rule (Yue-Ju et al., 2010), dynamic variability of soil quality methods (Larson & Pierce, 1994), nutrient index (Amara et al., 2017), soil health cards and test kit (Ditxler & Tugei, 2002) have been employed by researchers for soil quality assessment. Among these methods, soil quality index has been most extensively applied due to its quantitative flexibility and suitability for different types of soil and its coordination among the physical, chemical and biological attributes. Hence, soil quality indices are using at large scale to assess the impact of long-term management practices in particular crop production on the soil at a district; regional and provincial scale (Gong et al., 2015). Soil quality markers are vital component that incorporate soil function, and reflect environmental differences at large scale liable to influence soil quality. Though, lacking in consensus on which soil marker is useful for soil quality monitoring. For instance, Rahmanipour et al. (2014) had chosen soil erodibility, chromium and cobalt contents as quality indicators to assess soil quality, but were not found in other research. Liu et al. (2015) included some biological indicators like as acid phosphatase, and total counts of bacteria and AM fungi in minimum data set. However, soil pH, Pa, Ka, soil structure and SOC were considered as ideal soil quality indicators for the sugarcane production in Brazil (Cherubin et al., 2016). deFreitas et al. (2018) also reported that total sand, clay, micro-porosity, magnesium, calcium, soil pH, and organic matter considered as a sensitive soil quality indicators for sugarcane and native forest grown in northeastern São Paulo state, Brazil.
Certain soil environments have been shown to produce ultra-high sugarcane yields (i.e., >100 t ha-1). Although, it is unaware to which extent soil physical, chemical and biological properties contribute to create yield differences between the area under ultra-high yields and average yields within the same soil order (Bigott et al., 2019). Although, the study was meager to assess causes of yield variation and long-term impact of sugarcane mono-cropping on nutrient index, microbial activity and soil quality across the cane producing zones of Uttar Pradesh. Hence, this study was undertaken to (i) assess the chemical and biological properties of soil on different cane producing zones of Uttar Pradesh, (ii) evaluate the effects of soil attributes on nutrient index, soil quality and sensitivity measurement differ among the high, average and lower yielding areas and (iii) suggest the doses of balance fertilizer for different cane producing zones of Uttar Pradesh.