Integrated Plant Nutrient Supply for Sustainable Soil Health and Crop Productivity

R. S.  Antil, Professor and Head, Department of Soil Science, CCS Haryana Agricultural University, Hisar 125 004, India; E-mail: [email protected]) (Tel.) 01662-289278; (Fax) 01662-234952)

Abstract

Integrated plant nutrient supply (IPNS) (combined use of mineral fertilizers, organic resources viz. organic manures, crop residues, urban/rural wastes, composts, green manuring and biofertilizers) aims at the maintaining or adjusting plant nutrient supply to achieve a given level of crop production by optimizing the benefits from all possible sources of plant nutrients. Cropping system is one of the important components of sustainable farming system as it serves as a component of IPNS, for sustaining the productivity of the system through efficient nutrient cycling. Therefore, balanced fertilization must be based on the concept of the cropping system rather than a crop, so that productivity of a system as a whole is sustained. In Indian agriculture, there is mismatch between nutrient additions through organic resources and fertilizers and nutrient removals by crops and resulted a net negative balance of 10 million tones (Mt) of NPK. To minimize India’s current annual negative nutrient balance, increased use of organic resources along with chemical fertilizers would be essential and inevitable. Results of the long-term experiments indicated that IPNS technique increased productivity and profitability of different cropping systems and maintained soil fertility. The use of organic resources along with chemical fertilizers could play an important role in improving the efficiency of resource use, enhanced food grain production, maintenance of soil fertility and increasing the farmer’s income. The success of IPNS depends on the judicious use of different components of IPNS. In this paper, an attempt has been made to assess the importance and beneficial role of IPNS in sustaining soil health and crop productivity.

Background information

Escalating cost coupled with increasing demand of chemical fertilizers and depleting soil fertility necessitates the integrated use of organic and inorganic sources of nutrients for sustainable crop production and better soil health (Yang 2006, Antil et al. 2011, Antil 2012). Food grain production in India has increased from 52 Mt (1951-52) to 257.4 Mt (2011-12). A five fold increase in food grain production during the last 48 years combined with inadequate and imbalanced nutrient supply has led to extra mining of all the essential nutrients.  Extra mining of nutrients will have to be checked in order to maintain the soil health. Maintaining soil health is of utmost important to ensure food and nutritional security of the country. For most efficient use of fertilizers, all nutrients must be in balance. At all India level, the NPK consumption ratio (2011-12) was 6.5:2.9:1 against ideal ratio of 4:2:1. The distortion in NPK consumption ratio is more pronounced among zones and states. The problem of imbalance fertilizer use in case of secondary and micronutrients is even worse wherein the use is much less compared to crop requirement. So, we have to narrow down this nutrient use ratio in order to sustain the crop productivity (Tewatia, 2007, Sharma, 2011). So, we have to narrow down this nutrient use ratio in order to sustain the crop productivity. The green revolution  technologies have boosted the production in most of the crop. However, during the last couple of years, the yields have become almost static and no more increases in crop yields were obtained with optimum level of fertilizers (Antil and Narwal 2007, Antil et al 2011). The probable reason for this type of behavior in yield pattern of crops is due to changing climate, decline in organic matter content, imbalanced use of fertilizers, nutrients mining, low use of organic manures and increasing deficiencies of secondary and micronutrients. Even though during sixties, India has become self-sufficient on food front as against its large imports but our most valuable reserve – soil has been extensively over exploited. If such situation is allowed to continue for a longer time, there are chances that today’s productive land may become unproductive. The loss of soil fertility, in many developing countries, due to continuous nutrient depletion by crops without adequate replenishment poses an immediate threat to food and environmental securities. The balance sheet of NPK in Indian agriculture shows an annual nutrient depletion of 10 Mt NPK (Tiwari 2008). The most logical way to meet this negative balance is integrated use of both inorganic and organic sources of plant nutrients. Thus, the only way to check further nutrients mining and to sustain the crop productivity as well as soil health on long-term basis, is possible only through IPNS. In this paper, an attempt has been made to assess the importance and beneficial role of various organic resources (organic manure, crop residues, industrial waste, urban/rural waste, compost and green manuring) in combination with chemical fertilizers in sustaining soil health and crop productivity.

IPNS importance: Although IPNS is an old-age concept but its importance was not realized earlier due to low nutrient turn over in soil-plant system or almost all the nutrient turn needs of the then sustenance agriculture were not through organic resources which also supplied secondary and micronutrients besides major nutrients. The IPNS has now assumed great importance firstly because of the present negative nutrient balance and secondly, neither the chemical fertilizers alone nor the organic sources exclusively can achieve the production sustainability of soils as well as crops under highly intensive systems. In recent years a lot of emphasis has been laid in IPNS. What really brought IPNS into forefront was the decline in productivity of rice-wheat cropping system in South-Asian countries? The factor productivity for fertilizer has gone down in India both for rice and wheat. These data available from long-term fertilizer experiments in India also emphasize the need for continued application of organic manures for sustained food grain production in India. In the intensive agriculture, importance of IPNS is being magnified because of inadequate and imbalanced use of fertilizers causing negative nutrient balance, deletion of soil fertility and decline in fertilizer use efficiency (Tiwari 2008).

Nutrient deficiencies: The inadequate and imbalanced fertilizer use has caused widespread nutrient (N, P, K. S, Zn and B) de-efficiencies and deterioration in soil health in many parts of India. It has been estimated that at the all-India level, 63, 42, 13 and 40% soils were found deficient in N, P, K and S, respectively (Motsara 2002). On an average, 49% of soils have been found deficient in Zn, 15% in Fe, 3% in Cu, 5% in Mn, 33% in B and 13% in Mo (Singh 2001).

Nutrient balance: Soil fertility has declined due to decade of nutrient mining without replacing them with manure and fertilizers in sufficient quantities.Nutrient removals by crops far exceed nutrient additions through fertilizers. The total estimated NPK removal was about 28 Mt which resulting a net negative balance of about 10 Mt. Organic resources contribute about 4 Mt, which mean about 6 Mt negative balance has to be replenished by soil (Antil and Narwal 2007). Recently, Government of India has announced the target of doubling food production by 2025. It implies that for doubling the productivity, the nutrient removal would be more than double of present level to about 56 Mt. The gap between nutrient supply through all sources and removal would further escalate to more than 12 Mt from the present level of about 6 Mt, provided the contribution of organic resources is also doubled. Thus, the soil health would further aggravate, which needs urgent attention. Although it is not possible to replenish 100% of nutrients removed by the crops every year, even then the attempt should be made to maximize recycling of those nutrients which are likely to be deficient in future. The IPNS is the most effective way to further arrest the decline in nutrient mining from soils. The importance and beneficial role of IPNS components is discussed here. The components of IPNS are:

1. Balanced  fertilization
2. Organic resources (organic manures, crop residues, dung, composts, industrial wastes etc.)
3. Green manuring / legume in rotation
4. Bio-fertilizers

1. Balanced fertilization: Balanced fertilization must be based on concept of IPNS for a cropping system (Tiwari 2008) as this is the only viable strategy advocating accelerated and enhanced use of  fertilizer with matching adoption of organic resources and fertilizers so that productivity is maintained for a sustainable agriculture. The balanced fertilization could be achieved through application of multi-nutrient in balanced proportion from fertilizer and organic resources and more accurately and precisely through IPNS on cropping system basis. To increase the fertilizer use efficiency, crop yields and checks further mining of those nutrients, which are likely to be deficient in future, the balanced amount of fertilizers based on soil testing should be applied. Results of long-term fertilizer experiment indicated that application of balanced fertilizer and IPNS were the best tools for obtaining sustainability in crop yields (Singh et al. 2006, Singh 2010).

2. Organic resources: Use of fertilizers alone in the intensive cropping system creates infertility and unfavorable physical, chemical and biological conditions of soil. Soil health is deteriorating year after year and can be overcome by use of organic resources with fertilizers. Total estimated available nutrient value of organic resources in India is 12.80 Mt but the present utilization is about 3.75 Mt (Bhattacharyya 2007)which can be made available for agriculture use.  Thus, about 25% nutrient needs of Indian agriculture could be met by properly utilizing various organic resources (FYM, crop residues, urban/rural waste and green manuring) which are readily available for agricultural use. Hence, there is an urgent need to refine the technologies available on utilization of organic resources.

Results of long-term experiments on IPNS in rice-wheat cropping system in a Typic Ustochrept at PDCSR, Modipuram showed (Singh et al. 2005) that continuous cropping of rice-wheat system for 12 years with chemical fertilizers resulted in 3-4% decline in system productivity. Whereas, IPNS practices resulted in 3 to 17% increase in system productivity. Soil organic C content showed a decline in control (no fertilizer) as well as in recommended NPK+Zn applied to rice and NPK to wheat. Continuous cropping without P, K and S application resulted in a sharp decline in soil-P, K and S status. With the IPNS approach, soil organic C, available P, K and S content was increased over initial values. A summary of in the long-term fertilizer experiments showed that organic C increased appreciably under 100% NPK + FYM and the Organic C build up over the years (1971-82) under NPK + FYM application was 27-52% in alluvial soil, 60-92% in medium black, 45-77% in red soil and 174% in laterilte soils (Nambiar and Gosh 1984, Swarup 1998).

Results of a long-term experiment conducted at CCS Haryana Agricultural University, Hisar indicated that the application of organic manures (15t FYM or 7.5t press mud or 5t poultry manure ha-1 year-1) in conjunction with recommended dose of N increased productivity of different cropping systems (pearl millet–wheat, wheat-cotton, mustard–cotton, mustard– sorghum (fodder) and rice–wheat) and maintained soil fertility. However, application of organic manures alone resulted in poor yield of crops (Antil and Narwal 2007). It has been predicted that for each unit (0.1%) increase in soil organic C, the productivity of pearl millet can be increased by 273 kg ha-1 and that of wheat by 1591 kg ha-1 (Gupta et al. 2003, Antil and Narwal 2007). The organic C, available N, P, K, S, Zn, Mn, Fe and Cu contents of soil changed distinctively during 37 years of experimentation. Continuous application of FYM for a period of 37 years improved organic C, available P, K, S, Zn, Mn, Fe and Cu content of soil. Application of 15 t FYM or 7.5 t press mud or 5 t poultry manure ha-1 yr-1 with or without NP fertilizers could not sustain the initial level of N. However, soil fertility with respect to P, K and micronutrients (Zn, Mn, Fe and Cu) can be maintained (Antil and Singh 2007, Antil and Narwal 2007). These results indicate that fertilizer-N cannot be saved with the application of organic manures but the application of P, K and micronutrients fertilizers can be avoided. Organic C, available P and K contents of soil increased ranged between 0.03 to 0.06% year-1, 1.5 to 3.3 and 38 to 109 kg ha-1 year-1, respectively, with the application of 15 t FYM ha-1 yr-1 as a component of IPNS under various cropping systems (pearl millet – wheat, wheat – cotton, mustard – cotton,  mustard – sorghum (fodder) and rice – wheat) tested. The cumulative (3 years for all the cropping systems and 2 years for rice-wheat) increase in organic C content of the soil has been presented in Figure 1. It is not only the higher productivity and maintenance of soil fertility but is also economical and the benefit: cost ratio of FYM use ranged between 2.07 to 10.02 in different cropping systems. Thus, the technology of IPNS is a viable technology which can be easily followed by the farming community. But the success of IPNS depends on the judicious use of different components (Antil and Narwal 2007, Antil et al. 2011).

The soil organic C up to 30 cm depth significantly influenced by fertilizer and organic manure application, after 31 years of maize-wheat-cowpea (fodder) crop rotation. The soil organic C content of 0-15 cm soil layer was highest (6.5 g kg-1) in the NPK + FYM treatment. The NPK treatment had significantly higher soil organic C than the control and N treatments. In control and N-fertilized plots after 31 years of cropping, the soil organic C was similar to the initial level (4.4 g kg-1), whereas in NPK and NPK + FYM treatments the soil organic C increased over the initial level by 38.6 and 63.6%, respectively. The NPK + FYM significantly improved soil aggregation, soil water retention, micro porosity, and available water capacity and reduced bulk density of the soil at 0-30 cm depth (Hati et al. 2006). The study suggests that application of balanced fertilizers in combination with organic manures sustains a better soil physical environment and higher crop productivity under intensive cultivation.

The availability of FYM is limited in India; therefore, some other sources of organic manures were evaluated. In addition to increase in crop yields, the application of press mud, sewage sludge, poultry manure, castor cake and piggery manure also increased the organic C and nutrients content of soil (Antil 2012). Direct and residual effect of FYM and press mud cake on S nutrition in lentil-ground nut crop rotation showed that the FYM proved better than press mud                        in augmenting grain yield of lentil but the residual effect of press mud on groundnut was higher than FYM (Ghosh et al. 2005).  Soybean seed yield obtained with 25 kg N + 5 t FYM ha-1 was comparable to yield obtained with 25 kg N + 1 t neem cake ha-1 (Singh et al. 2006).

Crop residues: Crop residues are good source of plant nutrients and are important component of IPNS. Crop residues, besides supplying nutrients to the current crop, leave sustainable residual effect on succeeding crop in the system. Recycling of crop residues is a viable strategy to meet at least a part of the nutrient requirement of different crops under various cropping systems. The annual production of crop residues in the country is estimated to be 313 to 356 Mt with nutrient potential of 6.5 to 7.5 Mt of NPK along with secondary and micronutrients annually as organic source of nutrients ad also add to SOM pool (Tiwari 2008). About 30% N, 60-70% P and 75% K contained crop residues is available to the first crop and rest to subsequent crop. Crop residue addition improves soil organic matter content, nutrient use efficiency, soil physical properties (structure and moisture retention) and microbial and enzymatic activity(Antil and Narwal 2007). Residue management under IPNS has considerable effect on soil microbial biomass C which was enhanced if residue is incorporated with green manuring(Jaipaul and Negi 2006).Drop in soil organic matter due to limited return of biomass owing to residue burning has been identified as one of the key factor for un sustainability. Burning of crop residues due to lack of efficient and user-friendly technologies for in-situ recycling not only leads to loss of considerable amount of N, P, K and S but also contributes to the global NO2 and CO2 budget (Grace et al. 2002) and destruction of beneficial micro-flora of the soil (Timsina and Connor 2001). The only potent solution to meet out the problem of burning of crop residues in fields is to go for in-situ recycling or composting. Efforts have been made during the recent pasts to develop the efficient technology for crop residue management. In this direction, rice straw composting technology has been developed to meet out the problem of burning of rice straw in fields. Compost from rice straw can be prepared within 3½ months by dipping it for about three minutes in a solution containing 0.1% urea and 0.001% As per gillus awamori. Maintaining moisture at about 70% and doing two turnings after 15 and 30 days is essential for preparation of good quality compost (Antil and Narwal 2007).

Composts: The average quantity of rural and urban compost in India is 184.3 and 12.2 Mt having nutrient value of 2.56 and 0.427 Mt, respectively (Bhattacharyya, 2007). Pod yield of groundnut increased by 52% due to application of enriched (consists of cow dung, crop residue, rock phosphate, pyrite, urea) phospho-compost when supplemented with 50% NPK over ordinary compost in groundnut-wheat cropping system. Agro-industrial waste composts applied with NK fertilizers produced wheat grain yield comparable to that obtained with the NPK fertilizers, indicating a net saving of 100% of P fertilizer. Hence, instead of using fertilizer alone, the integrated use of compost and fertilizer could be more effective and sustainable for environment and agriculture (Dev Raj and Antil 2012).

Animal dung: Total population of animal in India is 920.63 million with dung production of 791.66 Mt having a nutrient (NPK) availability of 3.474 Mt. It has been estimated that about one third of the cattle dung produced is recycled in the fields and rest is burnt to meet the fuel demand which is a big loss. If this dung is properly managed, then the productivity of the soil can be increased. Therefore, farmers should be provided alternate source of energy for cooking so that maximum dung could be used as manure. This problem can be solved if the dung is used in biogas plant. The manurial value of biogas slurry is better than that of FYM (Bhattacharyya 2007).

3. Green manuring/ legume in rotation: Green manures mobilize soil nutrient reserves, creates conducive environment for soil microbes and saves on mineral nitrogen by fixing atmospheric N. Green manuring of Sesbania, sunhemp, mung and cowpea after harvesting of wheat in rice growing areas of India saved 40 to 60 kg N ha-1 and maintained soil fertility (Antil and Narwal, 2007). Green manuring of Sesbania or incorporation of mungbean residue resulted in recycling of 77-113 kg N ha-1 and increased productivity of the rice-wheat cropping system by 0.5-1.3 t ha-1 yr-1 and plant uptake by 12-35 kg ha-1 yr-1 over no summer crop in rice-wheat cropping system (Sharma and Prasad 2003).Grain yield of rice increased significantly with the application of fertilizers alone and with combined use of organic manure and fertilizers compared to control. Application of recommended dose of fertilizers (RDF) with 15 t FYM ha-1 produced significantly higher yield than applied with press mud or burnt rice husk or green manuring. Application of 50% of RDF with Sesbania green manuring produced rice grain yield comparable to that obtained with 100% of RDF indicating a saving of 50% of fertilizers (Table 1). The residual effect of FYM, press mud, green manuring and burnt rice husk was also observed on the grain yield of succeeding wheat crop and resulted in an increase of 3.5, 2.8, 3.3 and 1.2 q wheat grain ha-1, respectively. In addition to yield gains, integrated use of organic manures and fertilizer improved the organic C, available P, K and micronutrients content of the soil under rice-wheat cropping system. Cultivation of rice-wheat continuously for 7 years without any fertilization decreased (4.4 to 3.5 g kg-1) the total soil C over its initial level.

Table 1. Effect of different treatments on the grain yield of rice and residual effect on succeeding wheat crop.

aFYM = Farmyard manure; PM = press mud; GM = green manure; BRH = burnt rice husk.

Source: Mehla et al. (2007)

Incorporation of press mud with fertilizers resulted highest increase in soil C followed by FYM and green manure treatments. Continuous application of RDF + 15 t FYM ha-1, N150 + 7.5 t  press mud ha-1, 50% RDF + green manure for 7 years increased soil C by 1.7, 2.3 and 0.5 g kg-1 soil, respectively, in 0-15 cm soil over RDF only (Sekhon et al. 2009).

Green manuring with leguminous crops is not only beneficial in enhancing the yield but also improving the fertility of soil. Incorporation and decomposition of legumes has a solubilizing effect  of  N, P, K  and  micronutrients   (Zn, Mn, Fe and Cu)  in  the  soil  and  mitigates  the deficiency of different  nutrient  elements by  way of  recycling  of  nutrients, reduces the leaching and gaseous losses of N, in increasing the efficiency of applied plant nutrients. The value of N fixing legumes in improving and sustaining soil fertility is very important. In rice-wheat cropping sequence, incorporation of mungbean residues after picking the pods significantly increased yield over fallow treatment. The legume should be introduced in cereal based crop rotations; it would increase the yield and nutrient use efficiency in succeeding crops following legume and also reduce the mining of N from soils. Studies on IPNS in rice-groundnut system in acidic soils revealed that use of green manure along with blue green algae gave similar yield as was obtained with 60 kg ha-1 fertilizer N and maintained higher available nutrient throughout the year (Ghosh et al. 2005).

4. Bio-fertilizers: Bio-fertilizers are cost effective, eco-friendly and renewable sources of plant nutrients to supplement chemical fertilizers in sustainable agricultural system. Bio-fertilizers have an important role in improving the nutrient supply and their availability for crop production. They help in increasing the biologically fixed atmospheric N and enhancing native P availability to crop. Rhizobium is a potential bio-fertilizer for legumes, which saves about 25-50% of recommended dose of N and enriches soil with N for succeeding crop. Combined application of 20 t FYM ha-1 + 100% RDF + Azotobactorspp. + Pseudomonas striatarecorded significantly higher shelling (%), protein content, oil yield, pod and haulm yield over control and application of only FYM (@ 10 t ha-1) + Azotobactor  spp. + Pseudomonas striata + 50% RDF (Ghosh et al. 2005).  The use of bio-fertilizers should be done along with fertilizers and organic manures in legume and non-legume based cropping systems in order to sustain the crop productivity.

Conclusions

The application of organic resources in conjunction with chemical fertilizers increased the productivity and profitability of different crops and maintained soil fertility. The success of IPNS depends on the judicious use of different components of IPNS. IPNS has a great potential to offset the growing heavy nutrient demands, to achieve maximum yields and to sustain the crop productivity on long term basis. The soil health can be maintained with the balanced use of fertilizers along with organic resources besides getting higher yield. About 25% nutrient requirement of Indian agriculture could be met by utilizing various organic sources like cattle dung, organic manures, crop residues, urban/rural wastes, bio-fertilizers and green manuring. Hence, IPNS is the only viable option for sustainable agriculture. The IPNS could play an important role in order to meet out all objectives of sustainable agriculture viz. increased food, feed and fiber, profitability, efficiency of input use and maintenance of soil fertility and healthy environment.

Constraints

The Government is promoting the concept of IPNS, interestingly, farmers are also aware of the advantages if IPNS in improving soil health and crop productivity, but the adoption of IPNS on required level is limited due to the following constraints:

• increasing trend  to use cow manure as a source of fuel in rural areas;
• increasing use of crop residues as animal feed;
• extra cost and time required to grow green-manure crops;
• handling of problems with bulky organic manures;
• problems in timely preparation of fields when agricultural wastes and green manure have to be incorporated and their decomposition awaited;
• poor and inconsistent crop responses to bio fertilizers.

Future research needs

• Models of IPNS for different well defined agro-ecological zones and cropping systems be developed to provide guidance for rational and efficient fertilizer use.
• An elaborate program of monitoring changes in soil fertility should be established which can serve to periodically revise nutrient application rates to achieve maximum fertilizer efficiency, profitability yield sustainability and high quality so that today’s maximum yield could be transferred into tomorrow’s average yield.
• Residues recycling and in-situ generation of organic matter and enriched composting techniques is required.
• Location specific IPNS technology should be generated and effectively transferred to the farmers for sustaining productivity of various cropping systems.
• Causes of decline in crop productivity under various cropping systems-associated with deterioration of soil health and reduction in soil organic C stocks should be studied and possible measures should be found out.

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