BALANCED FERTILISER USE FOR SUSTAINING SOIL FERTILITY AND MAXIMIZING CROP YIELD A REVIEW

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1 Agric. Rev., 28 (4) : , 2007 BALANCED FERTILISER USE FOR SUSTAINING SOIL FERTILITY AND MAXIMIZING CROP YIELD A REVIEW V. Murugappan, M.R. Latha*, R. Jagadeeswaran, A. Bhaskaran and P. Malarvizhi Department of Soil Science and Agricultural Chemistry Tamil Nadu Agricultural University, Coimbatore , India ABSTRACT Higher yields and intensive cropping make high demands for nutrients from soil, which leads to depletion of soil nutrient reserve. K removal by the intensive cropping is disproportionately higher than the amount of K added through fertilizer as evident from the results of Long term fertilizer experiments in Tamil Nadu and elsewhere in India. The nutrients exported out of the farm in crop produces must be necessarily replenished to sustain soil fertility and therefore the production system for which balanced fertilizer application is the prerequisite and there is growing need for site specific balanced fertilizer recommendations according to the crop type, yield level and soil conditions. Balanced fertilizer schedule were developed for rice, maize, cassava, peanut, potato, tobacco etc. by the applications of mathematical models and decision support systems. The soil salinity or sodicity hinders the crop growth and yield. The industrial by-product Ferrogypsum from the effluent treatment plant of titanium industry was evaluated as a substitute for gypsum to alleviate sodicity besides its effect on increasing crop yields in paddy and groundnut. India may become the densely populated country in the world in another 50 years. It implies that the food production has to be increased proportionally to feed the burgeoning population. This increase in production has to come through higher yields by judicious use of inputs and increased cropping intensity. Evidently, higher yields and intensive cropping make high demands for nutrients from soil. This leads to depletion of soil nutrient reserve. The nutrients exported out of the farm in crop produces must be necessarily replenished to sustain soil fertility and therefore the production system. Native soil fertility alone cannot support the expected yield increase. Mineral fertilisers are the primary source of nutrients and usually contribute 35 to 50% to yield increases. Increasing productivity through fertilisers remains a wideopen option in India, since current intensity of fertiliser use in India is relatively low compared even to several developing countries. Therefore, sustaining the growth in fertiliser use is imperative to support the requisite gains in productivity. India ranks third in world after China and USA in total * Corresponding author: mrlatha@tnau.ac.in fertiliser consumption. N:P:K ratio in fertiliser use is 6.8:2.8:1 in India. Katyal (2001) compared this ratio with the ideal one 4:2:1 and indicated that the current fertiliser use scenario is unfavorable with respect to K nutrition of crops. Further, this ratio contrasts sharply with the ratio in which plants absorb N and K. Cereals for instance take up nitrogen and potassium in almost equal quantities. Vegetables and root/ tuber crops absorb even more potassium than nitrogen. However, most of the fertiliser recommendations in developing countries do not address this issue. K fertiliser amount is unduly undermined due to inadequate awareness on balanced fertilization, which is a serious concern in recent times. Data on crop response in longterm experiments revealed that during the last 25 years, response to N has decreased, whereas the response to P increased by 20 per cent and K by 160 per cent since it has been continuously mined without corresponding addition to soil (Krauss and Jin Jiyun, 2000). Balanced fertilizer use, if neglected may produce serious consequences in crop production. To avert the crisis, several research works have been carried out by authors, which are discussed in this paper.

2 Vol. 28, No. 4, Need for balanced fertilization In an undisturbed natural ecosystem, the natural supply of nutrients compensates their losses by run-off, leaching and volatilization. The agricultural ecosystem differs from the natural one in that the plant nutrients are constantly being removed and exported out of the farm in harvested produces. On one side, lack of sufficient awareness among farmers about the negative effects of high intensive farming without concern to conserve the natural resources or soil fertility has led to mining of soil nutrients which has caused the declining fertiliser productivity over the years. On the other side, population growth demands for an indispensable intensification of production systems, where the benefits of green revolution has not reached fully as well as in well endowed areas. The facts are clearly established in the results emanated from the Long Term Fertiliser Experiment (LTFE) conducted in major agroecological zones and soils of the country (Murugappan et al., 1999). These results have brought out the need for new innovations to bridge the negative gap between nutrients exported out of the farms and those returned to the soil. As a sample piece, the results of the LTFE of Tamil Nadu Agricultural University, Coimbatore are presented in Table 1. Each treatment in Table 1 represents a management system where different amounts of fertilizers are added. The results showed that in whichever system nitrogen is added in suboptimal amounts, the N balance is negative. In case of P, its balance is negative when P fertilization was not done. Thus optimal fertilization helps in maintaining a positive nutrient budget in case of N and P. In case of K, as indicated by the results presented in Table 1, the K removal by the intensive cropping is disproportionately higher than the amount of K added through fertilizer. The rate of decline in total and available P in soil in treatments involving continuous addition of N alone was very high in an intensive cropping (Table 2) (Santhy et al., 2001). This implies that judicious use of all nutrients in optimal amounts is essential to avert the ill effects of imbalanced fertilization. TABLE 1: Nutrient budgeting in a Long Term Fertiliser Experiment in Tamil Nadu (from 23 crop cycles of finger millet-maize-cowpea) Treatments Nutrient added per cycle Nutrient removed per cycle N P 2 O N P 2 O (kg ha -1 ) Control % N % NP % NPK % NP % NPK TABLE 2: Status of total and available phosphorus in soil under long-term fertiliser experiment Treatments Available P content (mg/kg) Total P content (mg/kg) Cowpea Finger millet Maize Cowpea Finger millet Maize Control % N % NP % NPK % NPK % NPK % NPK+ ZnSO % NPK + FYM % NPK + HW %NPK (S free)

3 256 AGRICULTURAL AGRICUTURAL SCIENCE REVIEWS DIGEST Results of Long Term Fertiliser Experiments conducted elsewhere in India have also brought out the fact that irrespective of whether fertiliser is added or not, intensive cropping deplete soil nutrients especially K. In Table 3, the scenario of crop removal and fertiliser use in Tamil Nadu is illustrated which exhibits a similar trend of negative balance in K in Tamil Nadu agriculture (Murugappan, 2000). The intensive cropping due to human pressure and the nutrient management strategy that are presently followed do not sustain the production systems. Thus, there is an urgent need for the identification of a new approach of innovations to ensure increases in production and at the same time conserve soil fertility and sustain the production systems. Developing basis for fertiliser recommendation In Tamil Nadu, farmers follow blanket fertiliser recommendation without site specificity. Reviewing the existing blanket recommendation for rice in Tamil Nadu emphasized the need for the revision of blanket fertiliser recommendation, which is crucial to increase yield of this staple food crop (Murugappan et al., 1993). Assessment of fertiliser requirements for a cropping sequence will be highly useful rather than developing recommendation for a single crop ignoring the crop effect in a cropping sequence. Since, the time interval between the crops is short, evolving fertiliser recommendation for the cropping sequence based on the initial soil fertility and providing a basis for assessing the fertiliser needs of crops in the sequence will be of immense use in ensuring scientific farming by the farmers. Fertiliser requirements for ricegroundnut-blackgram sequence were evolved using linear polynomial model (Natarajan et al., 1994). Several computerized models are available to arrive at fertiliser recommendation and to effect suitable soil fertility management practices based on nutrient stocks and flows and nutrient balance at farm level. Most models describing relationships between nutrient supply, uptake and crop yield address a single nutrient. In agricultural practice however, at least three macronutrients should be taken into account. This principle is the major cornerstone of the model Quantitative Evaluation of the Fertility of Tropical Soils (QUEFTS), which takes N, P and K into considerations, as well as the interactions between them (Janssen et al., 1990). QUEFTS has both empirical and theoretical components and describe the relationships between (i) chemical soil tests, (ii) potential NPK supply from soils and fertiliser, (iii) actual NPK uptake, and (iv) grain yield. Utilizing this computerized decision support system, the potential yield of an unfertilized rice crop at the native fertility of soil was estimated and results reveled that the plant nutrients requirement for the production of one tonne of paddy grain were 20.16, 4.04 and kg N, P and K, respectively with an average NPK ratio of 5:1:4.9 in the plant dry matter (Jagadeeswaran and Murugappan, 2001a). The regression coefficient between observed and predicted yield was 0.97 and for nutrient uptake were 0.97, 0.88 and 0.95 for N, P& K, respectively (Table 4). NUTMON-Toolbox is one such computerized software, which is used to monitor nutrient balance in farms and thereby identifying unsustainable practices/trends in soil fertility management. Using this software, an attempt TABLE 3: Nutrient removal by crops and fertiliser use in Tamil Nadu during 1997 Nutrient Uptake by crop Fertiliser use Use efficiency (%) Uptake from fertiliser (%) (lakh tones) N P O

4 Vol. 28, No. 4, TABLE 4: Observed and predicted rice grain yield and nutrient uptake for fertiliser levels. Fertiliser levels Grain Yield (kg/ha) N uptake (kg/ha) P uptake (kg/ha) K uptake (kg/ha) (kg NPK /ha) Observed Predicted Observed Predicted Observed Predicted Observed Predicted 0 : 0 : : 84 : : 168 : : 336 : r 2 value Initial Soil Status: KMnO 4 -N=236 kg/ha; Olsen-P = 10.7 kg/ha; NH 4 OAc- K= kg/ha was made for nutrient monitoring at farm scale to assess the level of nutrient sources and flows (Jagadeeswaran, 2002). The farm situation where the investigation was taken up necessitated evolving strategies and policies to mitigate the noticed negative signs in P and K balance in the farm. The possible options that were proposed for adoption are the use of slow release fertilisers, effectively managing crop residues and planning for converting the available crop residues in all forms into manures towards regulating the nutrient balance in the farm. In another study, the CERES rice model in DSSAT (Decision Support System for Agro technology Transfer) format was calibrated using the data of CO 47 and ADT 45 rice varieties (Susmitha, 2002). Using the calibrated model, optimum N fertiliser doses for these varieties for different locations (soil and weather conditions) within Tamil Nadu were calculated (Table 5). These calibrated models are valuable tools not only for optimizing N fertiliser recommendation but also for predicting the method and time of fertiliser application, planting date, planting density, quantity and scheduling of irrigation, organic manure etc. DSSIFER (Decision Support System for Integrated Fertiliser Recommendation), a user friendly computerized product, was developed as a useful tool in decision making in soil fertility management (Murugappan et al., 2004). Research information on soil test crop response on various crops formed the database for developing DSSIFER. With soil available macro and micronutrient levels, which are the input data for generating site-specific fertiliser recommendation, this software verifies the availability of soil test calibration for that sitespecific situation. Besides calculating the fertiliser requirements, DSSIFER software also generates recommendations on saline and alkali soil reclamation using the soil analysis input of ph and EC. Also from the irrigation water analysis, quality can be assessed using the software and its suitability for irrigation will be given as output with recommendation for the safe use of poor quality water. Evolving Balanced fertilizer schedule for crops The average grain yield growth has reached a plateau in recent years due to nutrient TABLE 5: Optimum N requirement for rice cultivars for various zones of Tamil Nadu predicted by CERES-rice Rice growing tracts CO 47 ADT 45 For maximum yield For maximum profit For maximum yield For maximum profit Cauvery Delta Zone Lower Bhavani ayacut North Western Zone PAP Command Area Western Zone * Economics were calculated using a price of per kg of N as 8.67 and one kg of rice as Rs

5 258 AGRICULTURAL AGRICUTURAL SCIENCE REVIEWS DIGEST TABLE 6: Results of test verification of ADT 36 and CO 43 rice Test treatments At location Ramapuram At location Manankorai Yield (tha -1 ) Profit(Rs.) Yield (tha -1 ) Profit(Rs.) Kuruvai season ADT 36 rice Blanket dose (120:38:38 kg N, P 2 O , ,511 kg ZnSO 4.7H 2 O ha -1 ) Fertiliser optima(175:54:50 kg N, P 2 O , ,164 kg ZnSO 4.7H 2 O ha -1 ) (4,013)* (4653)* Thaladi season CO 43 rice Blanket dose(150:50:50 kg N, P 2 O , ,791 kg ZnSO 4.7H 2 O ha -1 ) Fertiliser optima(165:63:65 kg N, P 2 O , ,520 kg ZnSO 4.7H 2 O ha -1 ) (2983)* (3729)* * Figures in parenthesis give the net returns over blanket dose due to fertiliser optima imbalances and deficiencies caused by intensive cultivation. Past experiences in fertiliser input and crop response studies have revealed that many times, the prescribed optimal fertiliser amounts for crops are not the real optimal levels. This is so because during experimentation, to formulate such optimal amounts, sufficiency of other plant nutrients in soil other than those considered in the experiment as variables, is not ensured. A systematic procedure was developed for identifying nutrient deficiencies (Hunter, 1980) based on which the treatment structure can be formulated for evaluating crop response and formulating balanced fertiliser schedule. It is imperative that reliable soil testing is essential for developing balanced fertiliser recommendations. Indeed, a large number of soil testing and crop response based research programme is established in the country, where much useful efforts were taken to develop calibrations correlating soil tests to fertiliser needs of crops. In these efforts, unfortunately, soil test crop response related field experiments did often focus only on two or three nutrients by which the importance of balanced fertilization was ignored. Balanced fertilization must consider all essential plant nutrients because if any one of the nutrients is deficient, it will not only limit crop yield and quality but also the use efficiency of other applied plant nutrients. Generally speaking, farmers tend to use more N than is needed and insufficient P and K, while ignoring secondary and micronutrients. Further in most of the field experiments, which are designed to optimize N, P and K for various crops, the level of a particular nutrient in the soil other than N, P and K is not in the initial soil analysis and the deficiency, if found in any case is not corrected before taking up the experiment. The fertiliser optima calculated based on such experimental data will be erroneous and therefore limit crop yields. Nutrient sorption studies carried out in ten bench mark soils of Tamil Nadu reveled that the identified nutrient deficiencies are specific to each soil series by which the fertiliser optimization studies in such soils may be initiated after corrective measures for these deficient nutrients (Murugappan et al., 2002). Besides, the knowledge on the capacity of soils to fix or complex certain plant nutrients will help in developing valid fertiliser optima. In the systematic approach, to detail the nutrient status of individual soil types, both greenhouse and field experiments are conducted using an optimum nutrient treatment (ONT) with all essential plant nutrients supplied and adjusted to an optimum level. Thus, no plant nutrient in that treatment limits crop yield during the experiment. Optimization of fertiliser amounts for rice through this systematic approach in Cauvery Delta Zone, the rice bowl of Tamil Nadu was done (Latha and Murugappan, 2001). The results revealed that rice yield as well as profit was higher with balanced fertilization by

6 Vol. 28, No. 4, TABLE 7: Effect of ferrogypsum on paddy grain yield, soil ph and exchangeable sodium percentage (ESP) of soil. Treatments Grain yield (kg/ha) ph ESP Control Gypsum Ferrogypsum Gypsum + FYM Ferrogypsum + FYM Gypsum + GM Ferrogypsum + GM SE(d) CD(p=0.05) FYM= Farm Yard Manure; GM= Green Manure systematic approach as compared to the blanket fertiliser recommendation followed in the state (Table 6). In the case of ADT 36 rice variety, there was an average of 23 per cent yield increase due to the adoption of newly evolved optima, which in monetary terms was Rs. 4,333/- per hectare more than that of the blanket recommendation. For CO 43 rice, this was 14 percent in case of yield increase, which in monetary terms was Rs. 3,356/- per hectare. In an experiment on fertiliser optimization for Cassava and peanut in North Western Zone Soils of Tamil Nadu, the fertiliser optima calculated were 50 % higher compared to blanket fertiliser recommendation followed at present in the state and evidently, net income was higher in this treatment (Kamaraj, 2002). This throws light on the information that there is a possibility for revising the state recommendation to ensure profit in these crops. N optimization study from a green house experiment with 15 N tagged urea, reveled that application of N in three splits would be optimal for turmeric (Jagadeeswaran et al., 2004). This observation lends support to a proposal for revising the presently followed five splits in the N fertiliser programme in turmeric. The field experimental data revealed that the presently followed state blanket recommendation (100% NPK) of 150 kg N, 60 kg P 2 and 108 kg O ha -1 is sub-optimal and there exist a scope to redefine the fertiliser optima for turmeric. Until precise fertiliser optima is established through proper fertiliser optimization studies, the 125 % of NPK levels, viz., kg N, 75 kg P 2 and 135 kg O shall safely be recommended to harvest better yields than what is presently harvested. In another study to evolve balanced fertiliser schedule for potato, application of 240:240:240:72 kg N, P 2, O and Mg ha -1 recorded the highest tuber yield (55.75 t ha -1 ). The yield increase was 149 per cent compared to state recommended level of 120:240:120:60 kg N, P 2, O and Mg ha -1 (22.4 t) (Sharmila Banu, 2002). Omission of Mg from this balanced fertiliser schedule still reduced the tuber yield to t ha -1. The nutrient requirement for potato was in the order of N>Ca>K>Mg>P>S and the N, P, K, Ca, Mg and S requirements for getting maximum economic yields were in the order of 6.5, 2.3, 4.9, 3.3, 2.6 and 2.3 kg t -1 of tubers, respectively. The results of the present study clearly indicated that the presently followed state recommended level of 120:240:120 kg N, P 2 O ha -1 with 60 kg MgSO 4 ha -1 is suboptimal. To ensure maximum yield, quality and net-income besides maintaining soil fertility, application of 240: 240: 240: 48: 80 kg N, P 2, O, Mg and S ha -1, respectively is recommended in the Hilly zone soils of Tamil Nadu. Similarly, results of the field experiment with cigar tobacco to ensure balanced fertilization revealed that each successive level of P, K and

7 260 AGRICULTURAL AGRICUTURAL SCIENCE REVIEWS DIGEST Mg fertilization improved the growth attributes and dry matter yield over the state recommended level. The cured leaf and whole plant yields evidently increased with the application of 60 kg N, 125 kg P 2, 250 kg O, 100 kg Mg and 150 kg S ha -1 with 43.2 per cent increase in yield over the state recommended level (Thamotharan, 2002). The nutrient requirement for cigar tobacco was in the order of K>N=Ca>Mg> S>P and the quantity were 38.5, 35.0, 26.7, 16.9, 4.9, and 2.7 kg t -1 of leaf yield, respectively. Economics of fertilization also supported the results that the net income was high with the balanced fertiliser schedule. Application of 60 kg N, 125 kg P 2, 250 kg O, 100 kg Mg and 150 kg S ha -1 enhanced the tobacco leaf yield, uptake of nutrients, nicotine content and leaf burning quality besides maintaining soil fertility. This fertiliser schedule would ensure balanced fertilization to cigar tobacco in Western Zone soils of Tamil Nadu. Fertiliser management for maximum yields in problem soils Improved nutritional management is required to harvest profitable yield on problem soils. For example, in calcareous soils lime induced iron chlorosis is the major constraint - where HCO 3 ions hinder the uptake and translocation of Fe in the plant (Patel et al., 1993). The presence of CaCO 3 directly or indirectly affects the chemistry and availability of nitrogen, phosphorus, magnesium, potassium, manganese, zinc, copper and iron (Marshner, 1995). Similarly, the salinity or sodicity hinders the crop growth and yield. In this aspect management of problem soils becomes essential to realize high yields. The industrial by-product ferrogypsum, (by-product from the effluent treatment plant of titanium industry and contains % gypsum and 10.24% Fe 2 O 3 ) was evaluated as a substitute for gypsum to alleviate sodicity besides its effect on increasing crop yield (Table 7) (Jagadeeswaran et al., 2002). Similarly, this by-product was also evaluated as a nutrient source for groundnut in calcareous soil (Jagadeeswaran and Murugappan, 2001b). CONCLUSIONS Research on balanced fertilization has reiterated the need for developing fertiliser schedule for all the crops through the systematic procedure. Balanced fertilization involves the whole array of nutrients. There is growing need for site specific fertiliser recommendations according to the crop type, yield level and soil conditions. The soil nutrient capital is not an inexhaustible resource and must be replenished according to the nutrient withdrawal. With the obligatory need for intensification of crop production, the demand of crops for readily available soil nutrient increases. The balanced fertilization helps the farmer to reap higher yields of better quality resulting in lower production costs and higher profits. Balanced fertilization improves fertiliser use efficiency and reduces losses of nutrients. The nutrient mined out of the soil has to be assessed and replenished through fertiliser application. Suitable fertiliser recommendations should be evolved to sustain soil fertility and crop yields. Strengthening the research on finding out sources of amendments for improving fertility of problem soils, which will also supply more than one nutrient to economize the crop production may be adopted as a means to improve problem soil and making wealth out of wasted lands. Future line of work Developing balanced fertiliser schedule to maximize both yield and profit for all crops and cropping systems, taking into account of native soil nutrient status Testing of balanced fertiliser dose derived through various approach under varying soil and agro-climatic conditions Use of modern tools viz., computerized decision support systems and models to identify the constraints and to propose solutions to mitigate the negative trends, if any in nutrient status.

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