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Sensitive biological indicators in different land use systems based on management goals

6.1 Sensitive biological indicators in rice-wheat cropping system in a Typic Haplnstept (productivity and environmental protection)

In a long-term experiment (7 years), condrrcted at the Indian Agricultural Research Institute farm (semi-arid, sub-tropical), New Delhi, important biological, chemical and physical indicators of soil quality were assessed and were later unified to a soil quality index (SQI). Two tillage methods, three water management techniques and nine nutrient management practices were evaluated for the study. For the identification of critical soil indicators with two primary goals—productivity (PCASQI-P) and environmental protection (PCSQI-EP), principal component analysis (PCA) was carried out and a soil quality index (SQI) was calcirlated using the Soil Management Assessment Framework (SMAF). The results indicated that management goal significantly influenced indicator selection and fluctuations in the index values of these indicators can provide early warning against deterioration of soil quality (Bhaduri and Purakayastha 2014). The sensitive indicators for rice and wheat with productivity and environmental protection are illustrated in Table 3.

Table 3. Sensitive biological indicators m rice-wheat cropping system based on management goals.

Crops

Management goals

Sensitive indicators

Rice

Productivity

MBC, PMN

Environmental protection

MBC, PMN, DHA

Wheat

Productivity

PMN, DHA

Environmental protection

MBC, PMN, DHA

[MBC-Microbial biomass carbon, PMN-Potentially mineralizable nitrogen, DHA-dehydrogenase activity].

6.2 Soil microbial biomass C and N and their mineralization rates as sensitive indicators in woody and grassland communities (sustainability and environmental protection)

In the subtropical Rio Grande Plains of southern Texas and northern Mexico, Me Culley et al. (2004) studied soil biological indicators, viz. soil respiration, potential C and N mineralization rates, microbial biomass in soil and nitrification rates in grassland and adjoining woody plant communities. The larger C and N pool sizes in the woody communities recorded higher annual soil respiration (SR) (745 compared to grasslands 611 g С nrtyr1), greater soil microbial biomass C (444 compared to 311 mg C’kg-1 soil), potential rates of N mineralization (0.9 compared to 0.6 mg N kg'1 d-1) and nitrification (0.9 compared to 0.4 mg N kg'1 d'1). The mean residence time of surface SOC in wooded coimnunities (11 years) was higher than that of grassland communities (6 years). It was reported that both labile and recalcitrant pools of SOC and total N increased when there was a shift from grassland to woody vegetation due to the higher flux as well as accumulation of C and N in the latter. The study concluded that soil respiration, potential C and N mineralization rates, and microbial biomass in soil were sensitive indicators of soil quality in woody plant communities and grasslands.

6.3 Glomalin as a soil biological indicator in undisturbed forest site vs. restored sites (soil sustainability)

Vasconcellos et al. (2013) studied arbuscular mycorrhizal fungi (AMF) and glomalin related soil protein (GRSP) to understand their potential as biological indicators of soil quality in an undisturbed forest site and three other sites at different stages of recovery after reforestation for 20,10 and 5 years. They observed that AMF species distribution, total-GRSP (T-GRSP) and easily extractable-GRSP (EE-GRSP) have influence on soil physical, chemical and microbiological attributes. A positive correlation between EE-GRSP and T-GRSP as well as total carbon, nitrogen, dehydrogenase and mease activity, microbial biomass carbon and microbial biomass nitrogen was recorded, especially in summer (Table 4). Macroporosity had a positive effect and soil bulk density had a negative correlation with EE-GRSP, signifying usage of either EE-GRSP or T-GRSP as biological indicator depending on the soil characteristics and management. The study demonstrated the effect of recovery period, seasonality and other soil attributes on AMF and GRSP distribution and indicated the use of glomalin as a potential soil biological indicator in the Atlantic forest of Brazil.

Table 4. Correlation coefficient between Glomalin content and soil biological indicators.

Variables

EE-Glomalin

T-Glomalin

Summer

Winter

Summer

Winter

MBC

0.4S

0.43

0.42

0.22

MB.N

0.57

0.62

0.41

0.40

Acid

phosphatase

0.42

0.38

0.36

0.064 ns

Urease

0.55

0.29

0.43

0.11 ns

Dehydrogenase

0.66

0.44

0.63

0.16 ns

6.4 Soil biological indicators under forest, extensive rubber plantations (jungle rubber), rubber and oil palm monocultures (sustainability and environmental protection)

Guillaume et al. (2016) studied soil biological indicators (basal respiration, microbial biomass, acid phosphatase) in Ah horizons from rainforests, jungle rubber, rubber (Hevea brasiliensis) and oil palm (Elaeis guineensis) plantations in Sumatra. The negative impact of land-use changes on the measured biological indicators increased in the following order: forest < jungle rubber < rubber < oil palm. Microbial C use efficiency was not dependent on land use systems. The basal respiration and SOC was non-liuearly related, i.e., SOC losses reduced microbial activity. Therefore, a meager reduction in C content under oil palm as compared to rubber plantations caused a great reduction in microbial activity. They concluded that the biological indicators thus studied can quantitatively assess resilience of agroecosystems with various use intensities and therefore can monitor soil quality.

6.5 Earthworm biomass as a sensitive biological indicator to tillage practices (yield and sustainability)

A modelling approach was used with production as management goal to predict the effect of agricultural management practices (pesticide applications and tillage) on soil functioning through earthworm populations. It was found that zero and reduced tillage practices can enhance crop yields while sustaining natural ecosystem functions. The results thus obtained suggested that conventional tillage practices have prolong effects on soil biota than pesticide control, provided the pesticide has a shorter half-life. They reported that an increase in soil organic matter could increase the recovery' rate of earthworm populations (Johnston et al. 2015). The earthworm biomass (gnr2) as well as crop yield decreased in the following sequence: zero tillage (27.1) > reduced (40) > conventional tillage (49.7) (Table 5).

Table 5. Earthworm biomass as a sensitive biological indicator of soil quality in different tillage practices.

Tillage

practice

Earthworm biomass (gm~!)

Productivity (tha-1)

Conventional

27.1

2.18

Reduced

40.0

2.63

Zero

49.7

2.95

6.6 Soil biological indicators under long term fertilizer and manure use in a sub-tropical inceptisol (productivity and sustainability)

Masto et al. (2007) analyzed microbial biomass carbon (MBC), microbial quotient (MBC/SOC), soil respiration, dehydrogenase and phosphatase activities in a 31 years field experiment involving manure and inorganic fertilizers treatments in a maize (Zea mays L.)-wheat (Triticum aestivum L.)- cowpea (Vigna unguiculata L.) rotation at the Indian Agricultural Research Institute, New Delhi, India and observed that the application of farmyard manure (FYM) plus NPK fertilizer significantly improved microbial biomass (124-291 mgkg'1) and microbial quotient from 2.88 to 3.87. Besides, soil respiration, dehydrogenase and phosphatase enzyme activities were also increased with FYM application. The response of MBC to FYM+100% NPK compared to 100% NPK was significantly higher than that for soil respiration (6.24 vs. 6.93 ml02 g"1 lr1), indicating MBC to be more sensitive indicator to FYM addition than soil respiration. Dehydrogenase activity increased as NPK rates were increased from 50% to 100%, but at 150% NPK, it showed a decrease. Phosphatase activity was more sensitive to season or crop type as compared to fertilizer treatment, although both MBC and phosphatase activity were increased with balanced fertilization. Calleja-Cervantes et al. (2015) worked in a vineyard with 13 years of continued application of composted organic wastes and observed changes in soil quality characteristics. They concluded that continuous longterm application of organic amendments affects soil quality positively through the augmentation of microbial activity.

6.7 Soil biological indicators sensitive to metal pollution (soil pollution assessment)

Epelde et al. (2008) studied the growth of Thlapsi caerulescens in metal contaminated soils and recorded shoot metal concentration as high as 337 mg Cd, 5670 mg Zn and 76.6 mg Pb per kg of diy plant weight. I caerulescens, under heavy metal contaminated condition, showed significant effect on soil biological parameters. In metal polluted sites, T. caerulescens recorded 154,115,140,37 and 164 per cent increase in the b-glucosidase, arylsulphatase, acid phosphatase, alkaline phosphatase and mease activity, respectively. They concluded that soil enzymes are sensitive biological indicators to evaluate the process of metal phytoextraction.

6.8 Mycorrhizal fungi fatty acid methyl ester (FAME) biomarkers, soil microbial biomass and enzymes as sensitive indicators to cover crop and tillage in a silty loam soil (environmentalprotection)

Mbuthia et al. (2015) studied the effect of long term (31 years) tillage (till and no-till), cover crops (Haity vetch; Viciavillosa and winter wheat; Triticum aestivum, and a no cover control) and N-rates (0,34,67 and 101 kg N ha'1) on soil microbial community structure, activity and resultant soil quality index using the soil management assessment framework (SMAF) scoring index under continuous cotton production on a silt loam soil in West Texmessee. Significantly, greater abundance of Gram positive bacteria, actinomycetes, myconhizae fiingi fatty acid methyl ester (FAME) biomarkers were observed in no-till as compared to tilled soil. Thesaprophytic firngal FAME biomarkers were significantly less abundant under no-till treatments resulting in a lower fungi to bacteria ratio. Different enzymes associated with C, N and P cycling (b-glucosidase, b-glucosaminidase, and phosphodiesterase) showed significantly greater activities under no-till as compared to tilled soil. Myconhizae fungi biomarkers showed significant reduction under increased N-rate and were much less under vetch cover crop compared to wheat and no-cover, suggesting them as sensitive indicators to crop types. Consequently, the total organic carbon (TOC) and b-glucosidase SMAF quality scores were significantly greater under no-till compared to till and under the vetch compared to wheat and no cover treatments, resulting in a significantly greater soil quality index (SQI) in the latter. Their results indicate that under a long-term no-till system and use of cover crops under a low biomass monoculture crop production system (cotton), mycorrhizal biomarkers, and soil enzymes like b-glucosidase, b-glucosaminidase, and phosphodiesterase are sensitive indicators to assess soil quality.

 
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