Soil Fertility

SOIL FERTILITY

Concepts of soil fertility and soil productivity 

• It  is  evident  from  the  early writing  of  Theophrastus  (372  –  287 BC)  even before  the advent of Christian era, Greek and Romans  realised  the  impact of soil on the growth of plants and made a mention about the application of  organic wastes and saltpeter (KNO3) for the plants. 

• The first experiment aimed at elucidating the increase in the weight of plant during its growth was reported by Nicholas – (1401 - 1446).  

• Jan Baptiste van Helmont   (1577-1644) attributed the  increase  in weight of willow shoot to water. 

• But a German chemist, Glauber  (1604-1668), who attributed  the growth of plants to the absorption of saltpeter (KNO3) from the soil. 

• John Woodward  (during  the year about 1700)  first conducted water culture experiments on spearmint and emphasized  that  the growth  factor  is some terrestrial matter but not the water.

The impact of fertilizers on wheat yields is best demonstrated by results from the Broadbalk Experiment, which was started in 1844 at the Rothamsted Experimental Station, the United Kingdom, and is still continuing . 

Justus von Liebig  (1803-1873) put  forth  the  ‘law of minimum’ which states that the yield is governed by the limiting nutrient and is directly proportional to the factor which is minimum in the soil. 

Mineral fertilization started about 1880, became a common practice in the 1920s and adopted on larger scale since 1950. In Europe, cereal yields have increased at an annual rate of 1.5–2.5 percent for many decades, from an average of 2 tonnes/ha in 1900 to 7.5 tonnes/ha in 2000.

As civilization moves to beginning of the twenty first century and as World’s population continues  to  increase,  the  importance of a continuing  increase  in  food production  is  obvious.  India  alone  is  contributing  more  than  a  Billion  people.  It means that our crop production must be at least doubled by the end of the century. There  are  two  options  open  to  us.  One  way  is  to  increase  the  area  under  the plough and the other to increase production per unit area. The scope is limited for the  first option. So greater attention will have  to be paid  to  the  increasing of  the production per unit area, per unit time. The strategy  is  to maintain soil  fertility and proper nutrient management without impairing soil quality (sustainable agriculture).

For many centuries until about 1800, the average grain yield was about 800 kg/ha, providing food only for a few people. The main problems were the low fertility of most soils (mainly caused by the depletion of nutrients) and the great yield losses from crop diseases and pests.

Efforts to achieve freedom from hunger became successful only after the discovery of the nutritional needs of crops in the mid-nineteenth century. In order to supplement plant nutrients of low fertility soils or poor soils, the value of manures was stressed and mineral fertilizers were developed.

Worldwide mineral fertilizer nutrient use is expected to increase from 142 million tonnes in 2002/03 to 165 million tonnes in 2009/2010, to 175 million tonnes in 2015 and to 199 million tonnes in 2030 (FAO, 2000a, 2005).

Soil fertility:   Soil  fertility  is defined as  the quality  that enables  the soil  to provide proper nutrient compounds in proper amounts and in proper balance for the growth of  specified  plants.  Soil  fertility  is  also  defined  as  the  ability  of  soil  to  supply adequately the nutrients normally taken from the soil by plants.

Soil fertility                                                                                  

• It is the inherent capacity of the  soil to provide essential chemical  elements for plant growth

• A  combination  of  soil  properties and  an aspect  of  soil  –  plant relationships.

• Soil  fertility  is vital  to a productive soil.  But  a  fertile soil  is  not necessarily  be  a  productive  soil. Many factors  can  limit production, even  when  fertility  is  adequate.

• For  eg.,  soils  in  arid  region  may be fertile but not productive. 

Permanent Manurial Experiments

The earliest long-term experiments called Permanent Manurial Experiments were started at Broadbalk field of Rothamsted Experimentation Station, Harpenden, England in 1843 by Lawes and Gilbert. These experiments were neither replicated nor randomised. Inspired by these studies, permanent manurial experiments on Rothamsted pattern were planned subsequently in several parts of the world. In India permanent manurial experiments were started at Kanpur (1885), Pusa, Bihar (1908), Coimbatore (1909) and at several other locations with principal aim to evaluate the long-term effect of organic and inorganic manuring on crop production and soil health.

The criteria of essentiality put forth by Arnon

        In  the  nature  there  are  nearly  one  hundred  and  three  elements.   Of  them nearly  ninety  elements  are  taken  in  by  the  plants. In  order  to  distinguish  the elements which are essential  from  those which may be  taken  in by  the plants but  are not essential, Arnon (1954) has laid down the following criteria. 

1.  The  plant must  be unable  to  grow  normally  or  complete  its  life  cycle  in  the absence   of the element.

2.  The element is specific and can not be replaced by another. 

3.  The element plays a direct role in plant metabolism. 

It appears  that an element would have  to be considered essential even  if  it  has  not  been  possible  to  demonstrate  that  it  fulfils  the  second  criterion  of essentiality.  For  ex.,  for many  bacteria,  diatoms  and  other  algae,  vitamin  B12  is known  to  be  essential,  but  the  essentiality  of  cobalt  per  se  has  not  been demonstrated.  According  to  this  criterion, molybdenum  and  chlorine  can  not  be considered as essential  though  they are  functional  in plant metabolism since  they can be  replaced by vanadium and halides  respectively. D.J. Nicholas gave more exact  definition  of  essential  elements  and  advanced  the  term  “functional  or metabolic  nutrient”  to  include  any  mineral  element  that  functions  in  plant metabolism, whether or not its action is specific. 

Element Essentiality was established by Year

H, O ---- Since time immemorial

C Priestly et al. 1800

N Theodore de Saussure 1804

P, K, Mg, S  Ca C. Sprengel         1839

Fe E Gris         1843

Mn JS Mc Hargue         1922

Zn       AL Sommer and CP Lipman 1926

Cu       AL Sommer, CP Lipman and  G Mc Kinney 1931

Mo       DI Arnon and PR Stout 1939

Na       Brownell and Wood 1957

Co       Ahmed and Evans 1959