Nutrient indexing of benchmark sites of Erode district in Tamil

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Introduction
During the Green Revolution era, the high input and high productive technologies together with high yielding, fertilizer responsive and photo-insensitive varieties have led to the yield revolution in grain crops.With concerted efforts, India had achieved the record production of 209 million tonnes of food grains in 1999-2000 with an all time high buffer stock of 40 million tones.Such a phenomenal increase in food grain production in India has commensurate with a six-fold increase in fertilizer consumption from 0.05 (1950) to 18 million tonnes (2002).However, the yield increase in crops to the addition of fertilizers begins to decline in the past decade as a direct consequence of imbalanced fertilization.
A holistic approach is to be adopted in order to maintain the balance between the crop removal and addition of fertilizers.Balanced fertilizer application is imperative for sustained productivity.In India, the problem is compounded by imbalanced fertilizer use, leading to widening of NPK ratio from 5.9: 2.4: 1 in 1991-92 to 10: 2.9: 1 in 1996-97 as against the optimum ratio of 4 : 2: 1 (Yadav, 2002).Most of Indian soils are deficient but excessive use   (Singh and Saha, 1995).Correction of micronutrient disorders is needed for sustainable farm production.In this context, it is appropriate to determine the nutrient balance in the soil to replenish the loss in nutrients suitably.Nutrient balance studies were undertaken in order to assess the emerging trends in nutrient deficiencies or toxicities in agroecosytems.

Experimental soil
The study area is P. Vellalapalayam village in Gobichettipalayam, Erode district.The village has a geographical area of 500 ha of which composed of 382 ha irrigated and 101 ha rainfed and the remaining area is being utilized for non-agricultural purposes.During the first phase of the delineation experiment, 200 surface soil samples (50 from rice-rice system and 150 from Sugarcane -Sugarcane-Turmeric System) were analyzed for pH, EC, organic carbon and available macro and micronutrients using standard protocols (Jackson, 1973).The major soil series occurs in the study area is Irugur (red non-calcareous) and Subramanian, K.S., Poongothai, S., Chitdeshwari, T. and Duraisami, V.P. were collected for the assessment of nutritional status.Young leaves of these crops were sampled dried, powdered and digested in diacid mixture.
After complete digestion, digested samples were diluted and assessed for macro and micronutrient contents (Subramanian and Charest, 1995).
During the second phase of the experiment, 15 benchmark sites comprising of 5 rice-rice system and 10 sugarcane-sugarcane-turmeric system have been monitored for the nutrient balance for the past five years.The post-harvest soil and plant samples drawn from the crop sequences had been analyzed for macro-and micronutrient contents in order to determine whether intensive cropping systems have caused deficiency or toxicity of nutrients.Yield and nutrient uptake pattern of individual crops in the sequence had been assessed.

Physico-chemical properties of benchmark sites
The 15 benchmark sites were analyzed for its physiochemical characteristics and the data are reported (Tables 1 & 2).The experimental soil texture varies from sandy loam to clay loam.These soils are intensely cultivated with rice-rice or sugarcaneturmeric.Soils have slightly acidic to neutral pH with no salinity hazard.Calcareousness in the soil is at moderate level and a few places showed no Nutrient indexing of benchmark sites of Erode district in Tamil Nadu (kg ha -1 ) (kg ha -1 ) (kg ha -1 ) (g ha -1 ) (g ha -1 ) (g ha -1 ) (g ha -1 ) (g ha The data indicated that the soil is basically rich in K & Fe.The available N, P and K were low, low-medium and medium-high status, respectively.The soil available N was 20-30 kg higher in sugarcane-turmeric system indicating the heavier fertilization than ricerice system.The experimental locations had sufficient levels of available micronutrients and sulfur status registering exceedingly higher values than the critical levels except in one site where the Zn content was found to be below the critical level.The soil available nutrient status was closely commensurate with the total nutrient pool.The overall nutrient status of the experimental soil has revealed that the benchmark sites have sufficiency levels of Fe, Mn, Cu, S and K.The Zn and P status were low to medium indicating that these nutrients may be limiting factors in the production system.

Profile characteristics
Soil profiles were dug out in three locations encompassing the all 15 benchmark sites and evaluated for their available nutrient status (Table 3).The profile characteristics were clearly distinguishable between red noncalcareous (Irugur series) and black calcareous (Chickarasampalayam series).All the three soil series were free from salinity.The organic status declined progressively with soil depth in all cases.The available nutrient status of different horizons in the three series appears to be similar.However, lime status and EC have conspicuously increased with increasing soil depth in Chickarasampalayam series.Such uniqueness was not observed in red sandy loam soils of Irugur or Sathyamangalam series.

Crop yields and nutrient removal pattern a. Rice -Rice System
In the Rice -Rice Production system, the average grain and straw yields registered were in the range of 4000-4500 and 6000-6500 kg ha -1 , respectively (Table 4).The yield potentials observed in the experimental locations were well above the State or National averages of rice crop.The trend of response was similar regardless of seasons or genotypes used by the farmers.The total uptake of nutrients by rice crop was 50-60, 25-30 and 75-80 kg ha -1 of N, P and K, respectively.The data clearly indicated that there is a luxuriant consumption of K in comparison to other nutrients.The total S uptake by rice-rice system was 43.5 kg ha -1 , indicating the necessity for replenishment through added sources of S. With regard to micronutrient uptake, the removal followed the order of Fe > Mn > Zn > Cu > B. Similar trend of response was reported earlier (Anon, 2003) b.Sugarcane -Sugarcane System In Sugarcane -Sugarcane system, cane yield, nutrient content and uptake in 10 benchmark sites in the farmers' holdings recorded were reported (Table 5).The cane yield ranged from 160 to 240 tonnes ha -1 with a mean average yield of 203 and 177 t ha -1 in plant and ratoon crops, respectively.The data indicated that the high productive potentials of benchmark sites that coincided with high fertility status of soils.The nutrient removal from the soil varied from 165-235, 40-52 and 280-330 kg N, P and K, respectively.Micronutrients removal was also several-fold higher than other crops that may tend to indicate that there is need for regular application micronutrients in order match the depletion in the soil native reserve.The cane yield and nutrient removal were slightly lower for the plant crop than the succeeding ratoon crop.The major nutrient content ranged from 1.0 to 2.0% for N, 0.2 to 0.4% for Nutrient indexing of benchmark sites of Erode district in Tamil Nadu P and 1.11 to 1.30% for K. Whereas the micronutrient content of the cane showed a wide variability.The values ranged from 12.0 to 15.8, 400-520, 19.7 to 26.8 and 4.19 to 10.7 mg kg -1 , for Zn, Fe, Mn and Cu, respectively.The crop removal pattern indicated that N is heavily depleted followed by K and P. Similar results were reported by Yadav (2002).With regard to micronutrients, Fe was depleted to a higher extent and order of the removal was Fe > Mn > B > Zn > Cu which reiterates the necessity for addition of micronutrients on a regular basis for yield sustainability.

c. Turmeric System
The turmeric rhizome yield varied from 4.8 to 6.2 t ha -1 which nearly double as that of the national average (Table 5).Turmeric rhizomes removed N, P and to the tune of 97, 47 and 215 kg ha -1 , respectively, to produce on an average of 5 tonnes of rhizome yield.Potassium uptake was 2.5 times as that of N and 5 times as that of P. The data clearly indicated that the soil K is being heavily depleted by turmeric and proper substitution of K is required to gain maximum yield advantage.Micronutrients have been removed in the pattern of Fe > Mn > Zn > Cu.

Nutrient Balance Studies
Nutrient balance studies were carried out for Rice -Rice system, and Sugarcane -Sugarcane -Turmeric System in order to determine the emerging deficiencies of nutrients (Table 6).The data have shown that in both intensive crop production systems, macronutrients were heavily depleted that has been suitably compensated with addition of inorganic and organic sources of nutrients.Consequently, there was a trend of positive balance maintained for macronutrients in most locations.However, negative balance of all micronutrients was observed in ricerice cropping system.On the other hand in Sugarcane-Sugarcane -Turmeric system, Fe, Zn and Mn have shown positive balance as these crops are being regularly fertilized with micronutrients in the form of FeSO 4 and ZnSO 4 in order to alleviate calcium induced deficiencies in soils.The overall data suggest that there is a need for balanced fertilization especially with the inclusion of micronutrients for the maintenance of soil fertility.Similar trend of response has been reported earlier (Singh and Saha, 1995).

Table 1 .
Soil physico-chemical characteristics and the total nutrient contents in the benchmark sites of Erode district No.

Table 5 .
Sugarcane and turmeric yields and nutrient uptake pattern in benchmark sites (Mean of 10 locations

Table 2 .
Available macro-and micronutrient status of benchmark sites in Erode district

Table 3 .
Predominant soil profile characteristics and available nutrient status representing 15 benchmark sites

Table 4 .
Rice yields and nutrient uptake pattern in benchmark sites (Mean of 5 locations)