The study, conducted by researchers at Banaras Hindu University in Varanasi and published in the journal Discover Soil, grew out of a growing anxiety about potassium mining in one of the world’s most intensively farmed regions. The rice-wheat cropping system that dominates the Indo-Gangetic plains supplies more than half of the food consumed in India, occupying roughly 27 percent of the country’s agricultural land. Yet fertilizer use in India has become badly skewed: between 1971-72 and 2021-22, nitrogen consumption surged 11.3-fold and phosphorus 14.2-fold, while potassium rose only 5.71-fold. The current national ratio of nitrogen to phosphorus to potassium stands at 6.7:2.4:1, far from the 4:2:1 ratio long recommended by the Fertiliser Association of India. An estimated 72 percent of India’s agricultural land is now considered potassium deficient.

Why does this imbalance matter? Potassium is not a minor player in crop physiology. It governs enzyme activation, water regulation, photosynthesis, and the transport of sugars, all of which feed directly into yield, grain quality, and the plant’s resilience to stress. When farmers skimp on potassium while piling on nitrogen, they quietly draw down the soil’s native reserves, a process scientists call potassium mining. Crop residues complicate the picture further: rice and wheat straw is extraordinarily rich in potassium, containing 80 to 85 percent of the nutrient taken up by the plant, and returning it to the field can substitute for 20 to 50 percent of potassium fertilizer. In conservation agriculture systems, where residues are retained on the soil surface and tillage is minimized, this recycling loop changes the chemistry of potassium availability in ways that conventional soil tests were never designed to capture.

To find out which chemical extractants best reflect reality under these conditions, the team turned to a long-term experiment established in 2012 at the university’s agricultural research farm. The site sits on sandy loam soils of the Typic Ustochrept family in a humid subtropical climate with about 1,110 millimeters of annual rainfall. The experiment followed a split-plot design with four crop establishment methods, ranging from full conventional tillage to full conservation agriculture with residue retention in both seasons, crossed with three nutrient management levels. After eleven complete crop cycles, the researchers sampled soil from all 36 plots at a depth of 0 to 15 centimeters and subjected it to a battery of twelve different potassium extractants.

The extractants spanned four mechanistic families. Distilled water and dilute salt solutions such as calcium chloride, barium chloride, ammonium acetate, sodium acetate, and sodium tetraphenyl boron target the potassium held in soil solution and on exchange sites. Multi-nutrient extractants, including ammonium bicarbonate-DTPA and the Mehlich solutions, pull several nutrients simultaneously. Acidic extractants, including strontium chloride mixtures and boiling nitric acid, attack the mineral lattice itself, releasing the non-exchangeable potassium locked between the layers of clay minerals. The logic is that plants do not simply sip from the soil solution; as roots deplete it, potassium desorbs from exchange sites and, over longer timescales, is released from mineral interlayers. A good soil test should mimic that whole cascade.

The results were striking. Boiling nitric acid extracted the most potassium, between 1,042 and 1,189 milligrams per kilogram of soil, followed by sodium tetraphenyl boron at 407.8 to 495.5 milligrams per kilogram, because both tap the non-exchangeable reservoir. At the other extreme, distilled water pulled out a mere 13.98 to 20.63 milligrams per kilogram. The workhorse ammonium acetate test extracted between 46.33 and 62.86 milligrams per kilogram, a middling figure that belies its global status. Among exchangeable-potassium extractants, barium chloride was the most aggressive, yielding 251.15 to 277.41 milligrams per kilogram, likely because barium is not preferentially adsorbed and does not collapse the expanded clay structures that hold potassium.

Correlation analysis revealed the real story. Sodium acetate emerged as the standout performer, correlating strongly with sodium tetraphenyl boron (r = 0.979), with relative grain yield (r = 0.927 to 0.984), with plant potassium uptake (r = 0.930 to 0.974), and with key soil indices such as cation exchange capacity, specific surface area, and organic carbon. The conventional ammonium acetate test performed respectably but less impressively, with correlations of 0.80 to 0.94 against plant indices. The acidic extractants fared worst: strontium chloride at 0.002 molar showed correlations as weak as 0.231 and no significant relationship with yield, while even boiling nitric acid, despite extracting the largest quantity of potassium, correlated poorly with what plants actually achieved. The researchers attribute sodium acetate’s advantage to its ability to pull water-soluble and exchangeable potassium along with a fraction of the non-exchangeable pool, capturing a broader spectrum of the potassium a crop can access during a growing season.

The team also established critical concentration thresholds using the Cate-Nelson statistical procedure, which partitions soil test values into ranges below which crops respond to fertilizer and above which they do not. Most extractants predicted critical levels with high coefficients of determination between 0.63 and 0.76. The critical value for ammonium acetate ranged from 51 to 54 milligrams per kilogram, while sodium acetate fell between 108 and 116 milligrams per kilogram. Boiling nitric acid produced the highest critical concentration, 1,224 milligrams per kilogram, but with the weakest predictive power, a coefficient of determination of only 0.35 to 0.46. Notably, critical values differed between rice and wheat for the same extractant, a reminder that soil test interpretation cannot be divorced from crop identity.

The agronomic findings were equally telling. Plots under full conservation agriculture, with residue retention in both seasons and minimal soil disturbance, outyielded conventionally tilled plots by 8.47 percent in rice and 10.72 percent in wheat, and recorded the highest potassium uptake, reaching 135.7 kilograms per hectare in rice and 112.4 kilograms per hectare in wheat. Residues appear to work through two mechanisms: their decomposition releases organic acids that dissolve potassium-bearing minerals, and the straw itself delivers a substantial potassium input back to the soil. Full conservation agriculture also raised cation exchange capacity by 19.4 percent relative to conventional tillage and boosted easily oxidizable organic carbon by 64.32 percent, changes that increase the number of adsorption sites available to hold and release potassium. Interestingly, additional potassium fertilizer did not significantly raise grain yields in this experiment, underscoring how much the residue-recycling system was already supplying.

The implications ripple outward from a single research farm in eastern Uttar Pradesh. Soil test calibration is inherently local, dependent on soil mineralogy, climate, and cropping system, and no single extractant works universally. But the message from Varanasi is clear: the global default test for potassium, ammonium acetate, captures only part of the story in soils where non-exchangeable potassium feeds crops, and it may systematically misjudge the potassium supplying power of conservation agriculture systems. Sodium acetate and the multi-nutrient extractants AB-DTPA, Mehlich I, and Mehlich III, which tap all or part of the non-exchangeable pool, tracked crop performance more faithfully. For a country where potassium fertilizer is expensive and farmers already under-apply it, a soil test that better reflects what the soil can actually deliver could save money, slow the mining of native reserves, and help sustain the rice-wheat system that feeds hundreds of millions. The researchers caution that their calibration must be validated across wider cropping systems, but the direction is unmistakable: the chemistry of measuring potassium needs to catch up with the agriculture it is meant to serve.

Subject of Research: Evaluation of chemical soil extractants for measuring plant-available potassium in long-term conservation agriculture rice-wheat systems

Article Title: Evaluating suitability of chemical extractants for measuring available soil potassium under long term conservation agriculture

Article References: Deepak, Jha, S., Singh, U. P., & Rakshit, A. (2026). Evaluating suitability of chemical extractants for measuring available soil potassium under long term conservation agriculture. Discover Soil, 3(1), Article 170. https://doi.org/10.1007/s44378-026-00330-w

Image Credits: AI Generated

DOI: 10.1007/s44378-026-00330-w

Keywords: soil potassium, chemical extractants, conservation agriculture, rice-wheat system, ammonium acetate, sodium acetate, soil testing, Indo-Gangetic plains, non-exchangeable potassium, critical concentration, Cate-Nelson, crop residue retention

What sets Pusa Rice Hybrid 60 apart from the majority of commercial rice hybrids is its genetic architecture. The hybrid was created by crossing Pusa 1S, a thermo-sensitive genic male sterile line, with PRR 418, an aromatic rice genotype. Thermo-sensitive genic male sterility, commonly abbreviated as TGMS, is a genetic system in which the male parent becomes sterile under certain temperature conditions, allowing breeders to produce hybrid seed without the need for a separate maintainer line. This is the defining feature of two-line hybrid rice technology, which simplifies seed production considerably compared with the conventional three-line system that relies on a sterile line, a maintainer line and a restorer line. By eliminating one parent from the seed multiplication chain, the two-line approach reduces the cost and complexity of producing hybrid seed, a factor that can translate directly into more affordable seed for farmers and faster commercial scaling for seed producers.

The agronomic credentials of the new hybrid are substantial. Across three years of evaluation in Bihar and Uttar Pradesh, Pusa Rice Hybrid 60 recorded an average grain yield of 59.24 quintals per hectare, a figure that places it among the more productive short-duration options available to farmers in the region. In comparative trials conducted under the All India Coordinated Research Project on Rice, the hybrid outperformed the national hybrid check US 314 by 11.6 percent, demonstrating that its advantage extends beyond comparison with inbred varieties and holds up against established commercial hybrids. Against the national varietal check CO 51, a widely grown cultivar, the hybrid delivered a 25.3 percent yield advantage. Most strikingly, it showed a 40.8 percent superiority over the zonal check in the coordinated trials, underscoring the magnitude of the genetic gain achieved by the ICAR-IARI breeding team.

Equally important for the eastern Indo-Gangetic plains is the hybrid’s maturity duration. Pusa Rice Hybrid 60 matures in approximately 120 days, placing it firmly in the short-duration category. This characteristic carries profound implications for cropping intensity, a critical consideration in a region where land holdings are small and farmers depend on squeezing multiple harvests from the same plot each year. A rice crop that matures early can be harvested in time for a timely sowing of the following wheat crop, preserving the integrity of the rice-wheat rotation that dominates agriculture across Bihar and Uttar Pradesh. Early maturity also reduces the crop’s exposure to late-season pests and terminal heat stress, and it can lower irrigation requirements by shortening the period over which the crop must be maintained in the field.

Yield alone rarely determines the commercial success of a rice variety in India, where grain quality commands a decisive premium in the market. Here too, the new hybrid performs impressively. Pusa Rice Hybrid 60 produces long-slender grains, a grain type strongly preferred by consumers in much of northern and eastern India, and it combines this with aromatic quality inherited from the PRR 418 parent. The hybrid achieved a milling recovery of 69.8 percent and a head rice recovery of 61.6 percent, both indicators of a grain that withstands processing without excessive breakage. Head rice recovery in particular is a measure of the proportion of intact kernels remaining after milling, and higher values translate into better prices for millers and, ultimately, for farmers. The hybrid also possesses intermediate amylose content, a starch characteristic associated with grains that cook to a tender, non-sticky texture, and the breeders report excellent overall cooking and eating quality.

Disease and pest reactions are a further dimension of the hybrid’s evaluation profile. In testing, Pusa Rice Hybrid 60 exhibited reactions to major insect pests that were comparable to those of standard checks, meaning that it does not carry unusual susceptibility that would require farmers to depart from established pest management practices. While the hybrid is not described as carrying specific resistance genes, parity with existing checks ensures that it can be integrated into current crop protection routines without added risk, an important practical consideration for the smallholder farmers who dominate rice cultivation in the target states.

The development of the hybrid reflects a coordinated effort across multiple ICAR-IARI stations and partner institutions. M. Nagarajan, based at the Rice Breeding and Genetics Research Centre at Aduthurai, is the lead developer of the hybrid, working alongside co-developers including Gopala Krishnan Subbaiyan and A. K. Singh of the Division of Genetics in New Delhi. The team’s division of labour illustrates the technical depth behind a modern variety release: Nagarajan and Subbaiyan drove the development of the TGMS line, while K. K. Vinod participated in the evaluation of both the sterile lines and the resulting hybrids. Data analysis was handled by Vinod, P. K. Bhowmick, Haritha Bollinedi and Ranjith K. Ellur, Rajeev Rathour of CSHPKVV Palampur contributed to the characterization and multiplication of the TGMS line, and Rakesh Seth at the institute’s Karnal regional station carried out the distinctness, uniformity and stability characterization required for formal registration. The work was published in the Indian Journal of Genetics and Plant Breeding as part of a report on varietal notification and germplasm registration.

The significance of the release extends beyond the performance figures themselves. India’s hybrid rice programme has historically been dominated by three-line systems, and the adoption of two-line technology has been slower than in China, where two-line hybrids occupy a large share of the hybrid rice area. Each successful Indian two-line hybrid strengthens the case for the approach, demonstrating that TGMS-based systems can deliver competitive yields and superior grain quality under Indian conditions. The registration of the Pusa 1S TGMS line and its deployment in a notified commercial hybrid also adds to the publicly available germplasm base, giving other breeding programmes access to proven genetic material for their own hybrid development pipelines. In a period when rice research worldwide is grappling with the twin pressures of shrinking land and water resources and rising demand, hybrids that combine early maturity with quality traits are increasingly viewed as a strategic asset.

For farmers in Bihar and Uttar Pradesh, the practical arithmetic is straightforward. A hybrid that yields roughly a quarter more grain than the leading varietal check, matures early enough to protect the following wheat crop, produces aromatic long-slender grain that fetches premium prices, and can be propagated through a simplified two-line seed system addresses nearly every major constraint in the region’s rice economy. The combination of high productivity, profitability and the potential for increased cropping intensity is precisely the package that agricultural planners have sought for the eastern Indo-Gangetic plains, a region that lags the northwestern states in productivity but holds vast untapped potential. As seed production of Pusa Rice Hybrid 60 scales up following its notification, the hybrid is positioned to become a promising cultivar for millions of rice farmers, and a showcase for what advanced two-line hybrid breeding can achieve in one of the world’s most important rice-growing regions.

Subject of Research: Development and evaluation of the two-line aromatic rice hybrid Pusa Rice Hybrid 60 for release in eastern India

Article Title: Pusa Rice Hybrid 60

Article References: Nagarajan, M., Subbaiyan, G. K., Vinod, K. K., Bhowmick, P. K., Bollinedi, H., Ellur, R. K., Seth, R., Rathour, R., & Singh, A. K. (2026). Pusa Rice Hybrid 60. Indian Journal of Genetics and Plant Breeding, 86(3), 381-382. https://doi.org/10.1007/s44489-026-00035-y

Image Credits: AI Generated

DOI: 10.1007/s44489-026-00035-y

Keywords: Pusa Rice Hybrid 60, hybrid rice, TGMS, two-line hybrid technology, ICAR-IARI, rice breeding, aromatic rice, grain yield, Bihar, Uttar Pradesh, short-duration rice, Indo-Gangetic plains