RIGHT WAY TO DIAGNOSE SOIL PROBLEM
Mood:  bright
So long we have kept our farming community almost in dark towards the need for right evaluation of inherent productive capability of plots, they possess, cultivate and live on. It is no doubt a fact, as we look back, that farmers seldom faced problems caused out of soil as long they followed rain dependent, indigenous cropping systems carried over generation to generation. Such systems and overall scenario has started to change as soon as irrigated multi-crop approach has been emphasised out of national urge to reach self-sufficiency in food grain production. From then onwards underground water resources have been tapped as exhaustively as possible installing deep tube wells and shallow tube wells and canal irrigation network have been laid creating dams and reservoirs. Side by side magical effect on use of inorganic fertilisers is extensively popularised and organic manure almost went into oblivion. Several cash crops are pushed in and indigenous crop varieties are gradually being replaced with HYVs. Use of highly poisonous plant protection chemicals turned into inescapable necessity only to overcome gradually invading problem of pests and diseases. Overall production status no doubt jumped up lucratively. Side by side a greedy as well as competitive feeling developed within farmers enjoying irrigation water to multiply production through increased use of water and inorganic fertilisers adopting high yielding varieties. And now, as inevitable phase of diminishing productivity is creeping in , we are advocating organic farming, aiming ecological & economical sustainability in production and at last we have become very much concerned about soil health. This is however, a good sign that at least our planners, scientists, technologists, extension experts, all at the helm of affairs, have stared to realise that soil, being a living media, requires diagnostic care and treatment. Services, so long made available to the farmers of India in the name of diagnostic care & treatment of a soil is ;soil testing service, basically designed to help farmers only to decide appropriate use of fertilisers and soil amendments for crops. Situation is such that a farmer if approaches with problem of diminishing productivity or crop failure (with no incidence of disease or pest attack) in his plot, immediate advice that would be served to him are “gets your soil tested”. None of such advisers ever realise the fact that routine soil test of mere surface soil sample of a plot indicating pH, salt content and available N,P,K would be of least use in right diagnosis of soil problem in anyway. Sudden or gradual decline of crop performance in a plot mostly relates to misbalance created in air-water balance within soil around root rizo-sphere specific for a crop. Plant roots and microbial populations are the two mutually dependent living beneficiaries of air-water balance, exclusively necessary for their normal growth. Such misbalance in air-water ratio is generally caused if natural drainage properties of a soil is disturbed or altered. The foremost diagnostic approach to locate the cause of sudden or gradual fall of crop performance should, therefore. Start with check up of internal drainage properties of a soil in purview. Studying of soil profile is thus inevitable as internal drainage properties of a soil is a function controlled cumulatively by surface, subsurface and subsoil properties of a soil. This may frankly be admitted that studying a soil profile to characterise & classify a soil as practised in soil survey work requires in-depth study of different morphological feature of soil, identifiable & measurable in a profile from surface to subsoil and on clear understanding of interpretative values of such features. In absence of such interpretative understanding, profile study turns into a mechanical job of measuring & recording different morphological feature with no application of mind towards qualitative evaluation. Amongst various soil properties that are checked & ascertained by studying a soil profile, Internal drainage status of a soil is to be considered as one of the most important criteria. Once diagnostic features of soil, indicative of soil drainage properties are known, proper rating of internal drainage status of a soil out of profile study become interestingly simple, easy and conclusive. In soil survey, we determine internal drainage status of a soil on the basis of comparative evaluation based on soil colour & on depth of occurrence of reduction mottles and or iron - manganese concretions within a profile. The drainage class so assigned is then corroborated with soil permeability (ascertained based on average textural & structural makeup of profile) along with position of ground water table. This is well within our experience that most of incidences of loss of productivity or sudden retardation of crop growth happen in irrigated, multi-cropped plots. Any attempt to find out possible cause of such incidences should essentially start with verification of internal drainage status of the soil in purview. Natural drainage of a soil is affected either due to excessive or uncontrolled irrigation leading to rise of water table and or soil structural degradation retarding natural permeability of soil. As a matter of fact, large portion of our irrigated lands otherwise moderately well drained are turning to imperfectly drained to poorly drained mostly due to indiscriminate use of paddy -paddy rotations. Typical tillage operations practiced in wetland paddy are aimed to slow down permeability; use of heavy tractor in field preparation further enhances the process through compaction. Repetition of summer paddy- aman paddy sequence of for consecutive years thus causes undesirable changes in internal drainage properties perpetually. Trying diagnosis of sudden or gradual decline of crop performance in any plot based on routine soil testing of surface soil sample is nothing but beating in the bush. Soil profile study can only guide us to right direction in such cases if we are really determined. Pranab Kumar Sengupta,Ex-Chief Soil Survey Officer Govt. of West Bengal,INDIA .