The salient achievements of AICRP on Long Term Fertilizer Experiments (AICRP LTFE) conducted on 17 cooperating centers with major soil types and vivid cropping systems under different nutrient management options and agro-ecological regions/ sub-regions are given here under.
- Yield data of rice-wheat system grown at Barrackpore, Pantnagar and Raipur, clearly demonstrated that application of P in addition to N is essential to sustain the productivity. However, at Pantnagar application of Zn is also inevitable for sustaining the productivity of rice- wheat system.
- In situ green manuring along with 50% NPK proved to be a good option to sustain the productivity of rice in areas where growing of green manure is possible by using monsoon rains. This has resulted in saving of 50% of the chemical fertilizer. However, 50% NPK+BGA did not work as good as 100% NPK, but it has benefited the next wheat crop as a source of nutrient on decomposition of Azola to some extent.
- At Bhubaneshwar and Pattambi application of FYM as soil amendment is more effective than lime. At other places also FYM was found to be superior to lime. The reason for more effectiveness of manure (FYM) than lime is that former has not only moderating effect but also supplies nutrients like N, P, K and other micronutrients. Thus, regular use of FYM could be better option than lime to sustain productivity of Alfisols.
- The balanced application of nutrient using organic manure is taking care of micronutrient cations by mobilization from the reserve source during decomposition of residual biomass added to soil. This is the reason at none of the centre so far deficiency of these nutrients was not experienced except at Pantnagar.
- The sustainable yield index (SYI) of rice and wheat crops at Barrackpore, Pantnagar and Raipur indicated that imbalanced nutrient application recorded significantly lower values compared to the balanced nutrient application. Even the application of 50% NPK along with biofertilizer could not sustain the yield of rice and wheat at these LTFE centres. The treatments showed the trend of SYI in the order of NPK+FYM > 150% NPK > 100% NPK > 100% NP > 100% N > control.
- In Alfisols group of soils, lowest SYI was observed in 100% N alone treatment. The reason for low SYI probably is due to deterioration of soil health in terms of pH and availability of P and K which affects the nutrient supplying capacity of the soil. The SYI values calculated were either near to zero or negative in 100% N treatment in maize, wheat, soybean, finger millet at almost each centres under Alfisols i.e. Palampur, Ranchi and Bangalore. Interestingly control (no fertilizer /manure) recorded little bit higher SYI values than the 100% N. Thus, results indicated that in any condition use of N alone should not be advised to farmers.
- In-spite of high amounts of carbon in Vertisols, available N content is always low compared to other soil having the similar amount of carbon. Study indicated that availability of N relativelydepend more on hydrolysable carbon. Therefore, hydrolysable pool of carbon should be considered to predict availability of N rather than total organic carbon.
- Nitrogen fractionation studies revealed that increase in nutrient dose from 50 to 150% and incorporation of FYM resulted in increase in all the fractions in soil which indicate that balanced nutrition would help in maintaining soil available N in more quantity which would help in sustaining the productivity.
- Phosphorus fractionation study indicated that Ca-P is most dominant in Vertisols (Jabalpur, Coimbatore and Akola) and absence of P resulted in decline of these fractions. It means P fractions are in equilibrium and responsible to maintain supply of P to plant.
- Potassium fractionation study revealed that due to application of K in less quantity than uptake by the crop, available pool of K is depleted at faster rate compared to other difficultly forms of K. In Vertisols in-spite of high status of non-exchangeable K and lattice K crop needs external supply of K through fertilizer. However, in Inceptisol the rate of decline in exchangeable K was seen less. On the contrary, increase in available K was observed in Inceptisols at Delhi and Pantnagar.
- The 100% NPK+FYM nutrient application significantly enhanced soil enzymatic activities, i.e. fluorescein diacetate (FDA), acid phosphatase and alkaline phosphatase. Similarly, microbial biomass C, labile, active as well as total C in the soil was found to be highest with 100% NPK+ FYM treatment. Thus it improved nutrient dynamics and C management index as far as long-term sustainability of crop yields are concerned and hence it signified the importance of balanced fertilization on soil C stabilization.
- Reduction of P dose to half in soils where P is accumulated due to continuous use did not have any adverse effect on productivity of both the crops in Ludhiana and Hoshiarpur districts of Punjab, Bangalore and Tumkur (Karnataka), and Jabalpur and Seoni district (Madhya Pradesh). The strategy used will not only reduce the input cost but also environmental pollution problem.
- Demonstration trials conducted at Palampur, Bhubaneshwar and Chhattisgarh centre of LTFE demonstrated that farmers are using half of the recommended dose with irregular use of FYM. Therefore, use of nutrients in requisite quantity is needed to sustain the productivity at higher level.
- The N balanced calculations made in soybean-wheat system at Jabalpur clearly demonstrated that soybean fixed 98 to 238 kg N and out of this almost 24-66 kg ha-1 N is contributed through biologically fixation in soil. Thus, left over N is used by subsequent wheat to some extent at Jabalpur.
- In-spite of increase in organic carbon and N status of soil at Jabalpur, decline in productivity of soybean was noted over the years. Analysis of weather data and their correlation with productivity revealed that increase in maximum temperature and erratic distribution of rainfall are responsible for decline in productivity of soybean whereas increase in wheat yield over the years can be ascribed to decline in minimum temperature during early growth stage of wheat.
- Soil physical properties played important role in growth of root and soil microbes. The results clearly demonstrated that application of chemical fertilizer resulted in physical condition of soil in terms of increase in soil aggregation mean weight diameter, infiltration rate and reduction in bulk density in comparison to control and imbalance use of nutrients.
- Soil aggregation and bulk density found to be closely related to water holding capacity and crop productivity. However, incorporation of organic manure further improved the physical condition of soil because of incorporation of more residual biomass and rhizodeposition due to higher productivity.
- Nutrient transformation and dynamics in soil is mediated through microbial activities. The impact of continuous fertilizer and manure application on microbiological activities revealed that there is an increase in population of bacteria, actinomycetes and fungi in soil supplied with nutrient in balanced manner. Contrary to this, application of nutrient in imbalanced way had adverse effect on microbial count. Increase in microbial count with balance nutrient application is due to availability of fresh food to microbes through root residues.
- Nutrient use efficiency has always been a focal point in agriculture research because of high production cost. The long-term fertilizer experiments (LTFEs) provide an opportunity to study such impact on nutrient response and nutrient use efficiency. It has been recorded that the nutrient use efficiency and responses are gradually declining over the years. For instance, the application of potassium in acid soils (Alfisols) is found to be highly essential to maintain crop productivity and soil sustainability. However, there is wide variation in efficiencies and response across the soil types and cropping systems.Thus, result clearly brought out that balanced and integrated use of nutrient is the only option to enhance the nutrient use efficiency which in turn would curtail expenditure on fertilizer and reduce the cost of production.
- From the laboratory study, it was observed that methane production is accelerated on application of nitrogen. Therefore, in order to minimize the CH4 productions under anaerobic condition full nitrogen dose should not be applied at a time especially when the soil is amended with fresh FYM or green manure.
- The basic study revealed that soybean-wheat cropping system in Vertisols found as carbon sequestering system and C accumulated in resistant pool is difficult to be accessed by microbes in this soil. This is the reason in spite of high organic C, available N status is less in Vertisols. However, the Alfisols and Inceptisols do not have such phenomenon.
- Studies on pesticide/ herbicide indicated that balanced use of nutrient reduced the half-life of herbicide and pesticides to 10-12 days and incorporation of FYM further reduced the half-life to 5 days because of more activities of microorganisms.
- The use of basic slag can be used as an alternate source than application of lime to sustain the productivity of acid soil. The material is easily available at reasonable price in the region, hence, use of basic slag should be promoted.
- Balanced use of chemical fertilizer did not have any adverse effect on soil organic carbon rather it has resulted in increase in SOC. Thus, data generated from AICRP LTFE at different locations in India indicated that use of chemical fertilizer did not deteriorate organic carbon of soil.
- Studies on carbon sequestration proved that application of chemical fertilizer in right way led to carbon sequestration and it varied from 50 to 300 kg ha-1 depending on soil type and nutrient management practice.
- The minimum amount (threshold) of carbon required to maintain initial carbon level in soil is dependent on initial content of carbon in soil and climate. The threshold carbon contents in different soils found were 2200, 2500, 1800, 3600, 3700 and 2000 kg ha-1 yr-1 respectively in soils of Jabalpur, Akola, Ranchi, Bangalore, Delhi and Ludhiana, respectively. The climate and soils of both IARI New Delhi and PAU Ludhiana are almost similar in nature but the threshold value of carbon of soil in former soils (IARI New Delhi) is more than later (Ludhiana) because of high initial carbon content (0.45% at Delhi) compared to PAU Ludhiana (0.23%).
- The threshold carbon determined for Mollisols (Pantnagar) was around 13000 kg ha-1 which is due to its very high initial carbon content (1.48%). Thus, threshold carbon value of soil is to a large extent depends on initial carbon content of soil. Sequestration of carbon takes place only when amount of carbon added is more than the threshold value of carbon in a soil.
- Soil indicators were identified by taking into account large number of soil physical, chemical and biological properties which are sensitive to management practices. The data from different centres was subjected to the principal component analysis (PCA). Soil indicators showed different key parameters for different soil types. For instance, pH, K, Ca, Mg and microbial biomass carbon for Alfisols; bulk density, SMBC and infiltration rate for Vertisols, whereas available nutrient (N, P, Zn and S) status and SMBC for Inceptisols are important soil indicators to be taken care of for improving sol quality.
- Soil quality index (SQI) is a relative numerical value which indicates the condition of soil at that point of time under a particular management and how it has been affected by the management practice. More is the index value better will be the soil quality. The SQI was estimated by using principal component analysis (PCA) and also giving weightage and scoring to the soil properties based on its relative contribution in productivity. In general, it has revealed that balanced nutrient application recorded higher SQI values than imbalanced treatments. However, incorporation of organic manure further improved the soil quality. In these treatments yields were also sustained at higher level at almost all the locations suggesting that balanced use of nutrient not only sustained the yield but also improved the soil quality.
- A new soil carbon and nitrogen turnover model has been developed by using the soil and crop dataset of long term fertilizer experiments of India. Soil carbon and nitrogen prediction model is controlled primarily by net primary production (yield), mean annual rainfall and temperature, texture (sand, silt, clay content), bulk density and soil initial carbon content. Soil carbon and nitrogen prediction model uses a yearly time step and the users have to define only initial soil carbon content. Model assumes soil carbon sequestration rate is the function of soil carbon content, net primary productivity, soil texture, rainfall, temperature and C: N ratio of residue. The model automatically computes the carbon and nitrogen turnover based upon these parameters and model output displayed in excel sheet.
- During last two years about five hundred front line demonstrations (FLDs) were conducted at tribal farmer’s fields under TSP programme. The interventions made by the scientists on nutrient management and the training resulted increase in crop productivity to the extent of 20 to 60 percent and also income and profit to a great extent.