Input supplied to Prof. Biswapati Mandal,BCKV on Soil Health Assessment methods

Soil quality assessment methods

Three (3) types of soil quality assessment approaches are in vogue.

1.      Modeling based approach

2.      Indicator based approach

3.      Integrated approach

Modeling based approach

The models provide a tool for predicting the change in outcome caused by the changes in input parameters. By using land-evaluation models, it is possible to predict the rates and direction of many soil-quality changes.

The two principal land-evaluation modeling approaches are:

(i)                 Empirical-based modeling, and

(ii)              Process-based modeling.

The basic idea of empirical modeling for land evaluation is that observed relations are quantified and these once analyzed (i.e., in a limited number of locations) are applicable for predicting future situations. However, this will not work unless there are sufficient data on which to base the inferences, so the methodology is not appropriate for new land uses or areas from which sufficient samples have not been taken.

The process-based models for land evaluation have been basically developed to simulate the growth of crops, along with associated phenomena that influence crop growth such as water and solute movement in soil. These simulation models are deterministic and based on an understanding of the actual mechanisms, but used to include a large empirical component in their descriptions of subsystems. The so-called Wageningen models (e.g., WOFOST and CGMS) are based on soil processes and plant physiology to predict yields under several production levels.

 But, since soil formation and soil processes are function of climate, modeling based approach will not hold universally fitting, i.e., a model developed for a particular region will not hold true for a land situation under altogether different macro-climatic or, even, micro-climatic conditions.

Indicator based approach

Indicator based soil quality assessment is much more widely acceptable one than modeling based approach. Indicators can be physical, chemical, and biological properties, processes, or characteristics of soils. They can also be morphological or visual features of plants. Selection of suitable indicators is the cornerstone of this type of evaluation.

The selection of indicators should be based on,

(i)                 Land use,

(ii)              Relationship between an indicator and the soil function being assessed,

(iii)            Ease and reliability of the measurement,

(iv)            Variation between sampling times and variation across the sampling area,

(v)               Sensitivity of the measurement to changes in soil management,

(vi)            Compatibility with routine sampling and monitoring,

(vii)          Skills required for use and interpretation.

(viii)       Cost of analysis

The list of different indicators to choose from as suggested by USDA is as below,

Physical

·         Aggregate Stability 

·         Available Water Capacity 

·         Bulk Density 

·         Infiltration 

·         Slaking

·         Soil Crusts

·         Soil Structure and Macropores

Chemical Properties

·         Reactive Carbon 

·         Soil Electrical Conductivity 

·         Soil Nitrate 

·         Soil pH 

Biological Properties

·         Earthworms 

·         Particulate Organic Matter 

·         Potentially Mineralizable Nitrogen 

·         Soil Enzymes 

·         Soil Respiration 

·         Total Organic Carbon 

The weaknesses of this approach are,

1.      Working with a whole lot of indicators is arduous

2.      Extraction of a Minimum Data Set (MDS), since done by statistical procedures, is subjected heavily to sampling and analytical accuracy.

3.      This does not take into account the interrelation or interaction between two or more interrelated indicators.

4.      It is not farmers’ centric per se, i.e., farmers perspectives regarding quality of their soil is given less scope. Only ease of estimation of an indicator is considered from farmers’ viewpoint.

   

Integrated approach

Considering the onerous task of development of relationships between all the soil-quality indicators and the numerous soil functions, a stepwise agroecological approach for soil-quality evaluation and monitoring can be much effective as well as accurate as proposed by De la Rosa (2005).

This is done in two steps,

Step 1:

Land evaluation is an appropriate procedure for analyzing inherent soil quality from the point of view of long-term agroecological changes. Within this complex context, land-evaluation models may serve as a first step to develop a soil quality assessment procedure. The first step will result in defining agroecological zones, land suitability, and vulnerability classes.

Step 2:

A short-term evaluation and monitoring procedure would be basically considered for the soil biological quality in each agroecological zone defined in the first step. By measuring appropriate indicators, changes in soil dynamic quality can be assessed.

Because soil biological parameters are most variable and sensitive to management practices, a monitoring system (observed change over time) would provide information on the effectiveness of the selected farming system, land-use practices, technologies, and policies. Also, enzyme activities have been found to be very responsive to different agricultural management practices such as no-tillage. 

Because of the complex nature of the soil and its high spatial and temporal variability, it is appropriate to develop soil-quality assessment based on biological indicators after the traditional land evaluation using basically physicochemical parameters. This agroecological approach should focus on dynamic soil aspects (biological factors) but with awareness of inherent soil aspects (physical and chemical factors).

Graphical representation of a stepwise agroecological approach for soil-quality assessment

(Soil Quality and Methods for its Assessment: Diego De la Rosa and Ramon Sobral,  https://www.google.co.in/?gws_rd=ssl#q=Soil+Quality+and+Methods+for+its+Assessment:+Diego+De+la+Rosa+and+Ramon+Sobral)

General remarks

The issue I wish to drive in additionally emphasizing gaps in our understanding for assessment of soil health is that we possibly never take into consideration the ‘interaction’ between different indicators. To elaborate this issue I stress upon the fact that we make measurement of the static indicators. Especially in respect of soil physical and biological/ enzymatic aspects, the interactions among the indicators, though may play vital role in crop productivity function, remain completely overlooked. This, to my understanding, needs focus for the future workers through detailed discussion among the relevant scientists to unravel major areas of such interactions in the first place. This will possibly further entail significant overhauling of the measurement and assessment techniques currently in vogue.  

Ghorai Dipankar & Sen, H.S. (2015). Phosphorus cycle and the environmental concern. SFE Newsletter, 2, July, 2015. Society for Fertilizers and Environment

Phosphorus cycle and the environmental concern

The role of phosphorus particularly its essential use in agricultural farm land (nearly 82 % of various uses) from a non-renewable and limited global stock of rock phosphate has been a major concern from the point of view of its inappropriate use or mismanagement vis-a-vis significant losses in various forms leading not only to exhaust the present stock within a few decades but also to cause serious environmental problems. The total production of mined phosphate rock in short-medium term for agriculture and industry is 20 MMT of P per year, and the P demand likely to increase at an average rate of 2-3 % per year to result in peak production by 2040, and eventually the supply to fall short of demand within finite time frame. It is not far that the P reserves will be controlled by countries like Morocco, Senegal, Western Sahara, China, South Africa, Jordan and US while farmers from the rest of the world have to depend on the terms set by them - a geo-political factor. 

Fig. 1. The phosphorus cycle (Source: http://www.euwfd.com/html/sources_of_pollution_-_diffuse_pollution.html)

The P cycle (Fig. 1) shows major losses in the form of runoff and erosion, leaching through soil causing global epidemic of eutrophication in fresh water, estuarine and near shore ocean environments, loss in potable water resources, aquatic biodiversity and formation of large ocean “dead zones“. Using P more efficiently and recovering it for reuse should contribute to reducing such pollution. The global reserve of rock phosphate was estimated as above 60000 MMT towards the end of the last century. Most of the countries including India has however no policy to manage P as a critical global resource, like what the EU Water Framework Directive has, urgently requiring them to be developed, as urged by the Global Phosphorus Research Initiative, which should, in the first hand, ensure positive P balance in farm lands. The present status suggests, if we take into account applications of mineral fertilizers and manures, the balance from some Western European countries is positive, particularly in the Netherlands, where it exceeds 39 kg P ha^-1 each year (Liu et al., 2008). For other countries in the region, the value ranges from 8.7 to 17.5 kg P ha^-1 annually (Johnston and Steen, 2000). China also achieved a positive balance around 1980 at the national level, in parallel with increasing application of synthetic fertilizers (Wang et al., 1996; Jin and Portch, 2001). In 2000, the national surplus of P in Chinese soils was estimated at an average of 16 kg ha^-1 (Liu et al., 2007). The total P budget for world’s cropland estimated in 2004 suggests (Liu et al., 2008) in the form of annual fluxes (MMT P): Inputs 22.9, Removals 12.7, Losses 19.8, and finally the Balance -9.6. 

Literatures cited

1.       Jin, J.Y. and Portch,  S. (2001). Recent agricultural and fertilizer developments in China. Paper presented at IFA Regional Conference for Asia and the Pacific, 10-13 December, Hanoi, Viet Nam.

2.       Johnston, A.E. and Steen, I. (2000). Understanding phosphorus and its use in agriculture. European Fertilizer Manufacturers Association (EFMA), Brussels, Belgium.

3.       Liu, Yi, Chen, J.N., Mol, A.P.J. and Ayres, R.U. (2007). Comparative analysis of phosphorus use within national and local economies in China. Resources, Conservation and Recycling, 51(2): 454-474.

4.       Liu, Yi, Villaba, Ayres, R.U. and Schroder Hans (2008). Global phosphorus flows and environmental impacts from a consumption perspective. Journal of Industrial Ecology, 12(2): 229-247.

5.       Wang, Q.B., Halbrendt, C. and Johnston, S.R. (1996). Grain production and environmental management in China’s fertilizer economy. Journal of Environmental Management, 47(3): 283-296.   

Dipankar Ghorai¹ & HSSen²

1.       SMS (Agril.) & Incharge, KVK (ICAR-CRIJAF),

Budbud, Burdwan, Email:dipankarghoraikvk@gmail.com

2.       Former Director, ICAR-CRIJAF,

Email: hssen.india@gmail.com,hssen2000@hotmail.com