Integrated Nutrient Management in Soybean: What INM Is, Trial Results, Manure Quantities and Cost-Benefit

Integrated nutrient management (INM) in soybean means feeding the crop from three sources together: a reduced dose of chemical fertiliser, organic manure such as FYM or vermicompost, and biofertilisers such as Rhizobium and PSB. ICAR-IISS Bhopal lists 50 percent of the NPKS dose plus 5 tonnes FYM per hectare plus Rhizobium as one of its two best modules in soybean-wheat. At Pantnagar, 50 percent RDF plus 10 tonnes FYM per hectare matched or beat full RDF alone, and full RDF plus FYM gave the highest yield. Start from a soil test and treat every replacement share as a starting point, not a rule.

Integrated nutrient management in soybean is a plan to meet the crop's nutrient need from three sources at once: chemical fertiliser, organic manure (FYM, compost, vermicompost, poultry manure) and biofertilisers (Rhizobium, PSB). The aim is to hold yield and profit while protecting soil carbon, nodulation and fertiliser efficiency.

Two points get lost on most pages. First, INM does not mean 'organic only'. In nearly every trial below the best result still contains some chemical fertiliser. Second, INM is not a fixed recipe. The share of fertiliser you can replace depends on how rich your soil is, how good your manure is, and whether soybean has grown in the field before.

The pattern in the opened trials is consistent. Organic manure improves soil structure and slowly feeds the crop, biofertilisers help nodulation and phosphorus uptake, and a reduced fertiliser dose supplies the quick nutrients. If you want the wider idea of how crops, soil and nutrients fit together, our guide on how to read your soil health card is the place to start.

Soybean is a protein-rich oilseed that responds to balanced feeding. The Pantnagar authors link low national soybean productivity to inadequate fertiliser use, poor recycling of organic sources and unbalanced use of fertilisers, especially micronutrients. INM tackles all three together: manure, biofertilisers and a measured fertiliser dose.

The Pantnagar paper quotes national productivity of 0.95 t per ha against a world average of 2.3 t per ha (FAI, 2006), and describes soybean seed as 40 to 42 percent protein and 20 to 22 percent oil. These are older figures, so use them for context only. The authors also say that continuous legumes with regular N and P fertiliser can leave native micronutrients short.

Their own soil was low in available nitrogen, low in iron and very low in boron, and the plots that received boron or iron yielded more than the control. Soils differ, so begin every INM plan with a soil test or Soil Health Card and treat any replacement share seen in a trial as a starting point, not a rule.

The components are organic manure applied before sowing, biofertilisers applied on the seed or in the soil, and chemical fertiliser applied as a basal dose, trimmed to what the soil test and the manure supply allow. Micronutrients and crop rotation are the support pieces that make the system hold.

Stage-wise fertiliser doses and the seed-treatment method sit in our soybean fertiliser schedule guide, and deficiency symptoms in our soybean NPK requirement guide. This post stays on the INM idea, the trial evidence and the economics.

Soybean gets atmospheric nitrogen only through nodule bacteria, so heavy nitrogen fertiliser is rarely the answer. Nodules must form early and stay active until pod fill, which is why inoculation, soil moisture and soil conditions matter more than a late dose of urea in an INM plan.

The Purdue Extension bulletin explains the biology clearly. Soybean rhizobia (Bradyrhizobium japonicum) are specific to soybean; other legume rhizobia will not nodulate it. Nodules become visible 10 to 14 days after colonisation, begin fixing around the V2 to V3 stage, reach full size in about four weeks, and keep fixing until they are 6 to 7 weeks old. Peak fixation comes at early pod fill. A functional nodule is pink or red inside. Moisture, soil temperature, pH, disease and some micronutrients all affect fixation.

This is the American side of the evidence, so use it for biology, not for Indian doses. The practical lesson is the same everywhere: cut open a few nodules at flowering. White or green inside suggests the nodule is not working. The article on Rhizobium, PSB and KMB for chana and other rabi pulses covers how the same bacteria behave in rabi pulses.

Field Check: Dig up three or four plants with a spade, not by pulling, at about 35 to 45 days. Wash the roots gently. Look for nodules on the main root and cut a few open: pink or red inside is a working nodule (Purdue). If nodules are missing and the leaves are pale from the bottom, check waterlogging, soil pH and inoculation before adding urea.

Opened trials from ICAR and agricultural universities show that cutting fertiliser to about half and adding FYM or vermicompost with Rhizobium and PSB can hold or raise soybean yield. In several trials, full RDF plus FYM still gave the highest yield. The saving is real, but yield gains need the organic part to be present.

Read the table with care. The base dose is different in each trial, and the soils are different (silty clay loam at Pantnagar, rainfed Vertisol at Jabalpur, cold-valley soil in Kashmir). Compare the direction of the results, not the exact figures. ICAR-IISS also says the choice between its two best modules, INM and balanced fertilisation, depended on whether the farmer has FYM.

At Pantnagar, adding 10 t FYM per ha to half the recommended fertiliser lifted seed yield from about 2.4 to 3.2 t per ha and raised net returns by about Rs 7,000 per ha. Full RDF plus FYM was the best treatment on yield and returns. This is the cleanest published cost-benefit set I could open.

The Pantnagar paper (Chaturvedi et al., Indian Journal of Agronomy, 2010) ran 14 treatments over two kharif seasons on a silty clay loam, pH 7.3, with medium organic carbon (0.79 percent), low available nitrogen and very low boron. The two fertility levels were 50 and 100 percent of the recommended dose (RDF), with FYM at 10 t per ha. Every plot including the control received Bradyrhizobium culture. FYM was applied 15 days before sowing.

Three things stand out. Half RDF plus FYM matched and slightly beat full RDF alone (about 3.2 against 3.1 t per ha) with a similar cost. FYM alone at 10 tonnes still gave a big jump over the control. And the best treatment of all kept full fertiliser and added FYM, so INM can add yield, not only save fertiliser. The prices behind the economics are from 2003 and 2004 (grain at Rs 9,300 per tonne), so use the ratios, not the rupee values.

The same paper reports that FYM and micronutrients helped maintain soil fertility and the rhizosphere microbial population, and that FYM or boron or iron with 50 percent or full RDF improved the unsaturated fatty acid share of the oil.

At JNKVV Jabalpur, 1.5 t per ha of vermicompost enriched with PSB and Rhizobium, plus only the balance of the recommended fertiliser, gave the highest soybean grain yield, 1,923 kg per ha. FYM at 4 t per ha with the same enrichment came second and poultry manure 1.5 t per ha third. All beat the absolute control.

The JNKVV paper (Sharma et al., 2018) used variety JS-9752 at 75 kg seed per ha, 45 cm rows, and a full dose of 25:60:40 kg N:P2O5:K2O. Manures were analysed before use: FYM about 0.48 percent N, 0.18 P2O5 and 0.45 K2O; vermicompost about 1.5, 0.62 and 1.02; poultry manure about 1.8, 1.6 and 1.4 (2016 values). Fertiliser was urea, SSP and muriate of potash.

The authors report 41.0 pods per plant and 2.83 seeds per pod in the best treatment against 30.2 and 2.30 in the control, and plant height of 63.4 cm against 43.3 cm. Full RDF ranked fourth; its exact yield was not in the text I could extract, so it is not quoted.

Less than most farmers expect. In the JNKVV analysis, FYM held about 0.48 percent N, 0.18 percent P2O5 and 0.45 percent K2O, vermicompost about 1.5, 0.62 and 1.02, and poultry manure about 1.8, 1.6 and 1.4. Poultry manure is richest, FYM leanest. Test your own manure, because quality varies.

The JNKVV paper converted each manure rate into kilograms of nutrient and worked out the balance of fertiliser needed to reach the full dose of 25:60:40 kg N:P2O5:K2O per ha. The table gives the 2016 values as printed in the paper.

Read the pattern. In the best treatment, vermicompost covered most of the nitrogen, while the fertiliser still supplied about 51 kg P2O5 against a full dose of 60. So manure took over nitrogen first, and phosphorus stayed close to the full dose. That is a useful rule of thumb from this trial: replace nitrogen with manure first and be slower to cut phosphorus.

A second point: five tonnes of FYM at 0.48 percent N carries only about 24 kg of nitrogen. Its larger value is organic carbon, slow release and soil biology, which is also why FYM alone at 10 t per ha still gave a big jump over the control at Pantnagar.

No. INM often matches full fertiliser and builds soil better, but several trials show full RDF still gives the highest or equal yield. The honest case for INM is similar yield, better soil carbon, lower fertiliser spend and, in some trials, better oil and protein, not guaranteed higher yield in every season.

In the Kashmir valley trial (Singh et al., 2009), RDF gave markedly higher growth and grain yield than the other treatments but was statistically at par with Rhizobium plus Azotobacter plus PSB plus 5 t FYM per ha, and with Rhizobium plus PSB plus FYM. The best treatment for quality was the four-part combination, which raised oil content 6.9 percent, oil yield 9.7 percent, protein content 9.9 percent and protein yield 9.6 percent over the control.

The Sharma and Prasad study compared organic, inorganic and integrated systems for six crop cycles at Bhopal and Raipur. The result was mixed on yield and clear on soil.

So at Bhopal soybean did slightly better under organic and INM, and at Raipur full fertiliser did marginally better. Soil health improved in both organic and INM systems. For a farmer, that suggests INM is a sensible middle path: the yield risk is small and the soil gain is real.

Opened trials used 4 to 10 t of FYM per hectare, 1 to 2 t of vermicompost and 1 to 2 t of poultry manure. ICAR-IISS uses 5 t of FYM per hectare in its INM module, about 2 tonnes per acre. Always use well-decomposed manure and apply it before the last ploughing or at sowing.

Manure quality varies, and the JNKVV analysis (FYM at about 0.48 percent N) shows why: 5 t per ha brings only about 24 kg N. If your FYM is half-rotted or full of straw, the benefit shrinks and it can tie up nitrogen briefly. Decompose heaps early; a compost activator is one way to speed up farm waste, and its page gives 1 to 1.5 L per metric tonne of waste diluted in 200 L of water.

When FYM is short, ready-made vermicompost is an option. The product page lists 500 to 750 kg per acre for cereals, pulses and oilseeds, which is about 1.2 to 1.85 t per ha, so the 1.5 t per ha used at JNKVV falls inside that range (my conversion). Count nutrient credit only from a tested analysis of the lot you buy. Our manures and soil conditioners collection lists what is available.

Rhizobium builds the nodules that supply nitrogen, PSB helps release phosphorus bound in the soil, and potash-mobilising bacteria (KSB or KMB) do the same job for potassium. Rhizobium and PSB appear together in nearly every INM trial opened here. None of the soybean trials opened tested KSB.

Every INM trial above used Rhizobium, and most paired it with PSB. The ICAR-IISS module uses Rhizobium on soybean and PSB on the wheat that follows. Pantnagar inoculated every plot with Bradyrhizobium, control included, so its yield gains came on top of inoculation. TNAU's soybean package lists both Rhizobium and phosphobacteria among its biofertiliser inputs.

• Rhizobium. A Rhizobium biofertilizer is the first biofertiliser to put in place. Katyayani's Rhizogen page lists soybean among its crops. Rhizobium for soybean is crop-specific (Purdue), so a mixed-pulse culture is not a safe swap.
• PSB. A PSB fertiliser pairs with Rhizobium in the INM trials. Katyayani's Soluphos page describes it as converting insoluble soil phosphorus into a form plants can use.
• Potash mobilising bacteria. Katyayani's potassium mobilizing bacteria page says the product mobilises available potassium near the roots. Since no soybean INM trial opened tested it, treat it as an optional add-on, not a core part of the plan.

Application method, doses and sequence are in our soybean fertiliser schedule guide. For the full live range, see our bio fertilizer collection. Keep any culture away from heat and sun, and check the pack date and strain before buying.

Residue and rotation spread the benefit of INM across seasons. Soybean leaves residue and nodule nitrogen for the next crop, and a legume or cereal rotation breaks pest and disease cycles. In the IISS module, soybean gets the 50 percent plan and the following wheat gets 75 percent of NPKS with PSB.

The IARI trial compared four soybean-based systems and found that soybean-wheat-mungbean gave significantly more pods per plant and seed yield than soybean-wheat-fallow, and that soybean in the mungbean system took up more N and K. A short summer legume between wheat and soybean seems to help. Returning soybean stover to the soil, rather than burning it, keeps the carbon and nutrients in the field.

The ICAR-IISS module plans the wheat dose at 75 percent of NPKS with PSB after INM soybean, so the wheat crop is planned, not left to residual soil nitrogen. Set the dose from your own soil test. The post on crop rotation examples for Indian farms has the broader rotation templates, wheat sowing time and seed rate fits the next step in a soybean-wheat sequence, and if chickpea follows soybean, see chickpea farming in India and the chana biofertiliser guide.

INM does not always cost less. In the opened figures, adding FYM to fertiliser raised cost a little and raised net returns a lot. At Pantnagar, adding 10 t FYM to full RDF added about Rs 515 per ha of cost and about Rs 6,846 per ha of net return (my subtraction from the table).

The ICAR-IISS figures cover the soybean-wheat system for the year, so they are larger than the Pantnagar single-crop figures. Both sets are old-price research results. Re-run the sum with today's fertiliser, FYM, labour and grain prices before you decide. A simple test: how many rupees of fertiliser does your FYM replace, and does yield stay the same?

Yes, but expect a different yield and cost profile. In the opened Bhopal and Raipur results, organic management gave similar soybean yields to inorganic (1,380 against 1,222 kg per ha at Bhopal, 2,068 against 2,250 at Raipur) and built the most soil carbon, but it needs steady manure supply and certification.

The Sharma and Prasad work reports organic management raised soil organic carbon 33.9 percent and available phosphorus 273.1 percent over six cycles, which is large. The abstract does not say which phosphorus sources were used. A phosphorus source such as rock phosphate can be useful in organic plans; our organic fertilizer collection lists rock phosphate, organic potash and other inputs. Do check any product against your certification standard first. The NPOP organic certification guide explains how.

In organic soybean the biofertilisers, compost and rotation do most of the nutrient work, and pest and weed management become the limiting factor. This guide does not cover them; it covers nutrition.

The costly INM mistakes are cutting fertiliser without adding enough organic manure, using weak or half-rotted manure, cutting phosphorus too far, applying FYM too late, and skipping Rhizobium in a field with no soybean history. Each one lowers the return the trials report.

• Cutting fertiliser without manure. Half RDF alone gave 2.41 and 2.50 t per ha at Pantnagar against 3.15 and 3.36 with FYM added.
• Weak manure. FYM at about 0.48 percent N gives a modest nutrient credit; its value is carbon and soil biology.
• Applying FYM late. Pantnagar applied FYM 15 days before sowing, so plan heaps and spreading early.
• Cutting phosphorus too far. In the best JNKVV plot, fertiliser still supplied about 51 of the 60 kg P2O5.
• Skipping Rhizobium in a new field. Purdue says that where soybean has never grown, the specific rhizobia must first be established by inoculation.
• Copying one replacement share everywhere. IISS used 50 percent NPKS with 5 t FYM, while the IARI trial found 25 percent RDF plus 50 percent of the nitrogen through FYM gave the highest yield. Soils and manure differ, so test and adjust.

Conclusion

Integrated nutrient management in soybean works when the three parts are all present: a trimmed dose of fertiliser, decomposed FYM or vermicompost, and Rhizobium with PSB. ICAR and university trials show that half-dose fertiliser with FYM and biofertilisers can match full fertiliser and often returns more per rupee, though full fertiliser plus FYM still gave the top yield at Pantnagar. Start from a soil test, replace nitrogen with manure first, and cut phosphorus slowly.