Real-Time Nitrogen Management in Transplanted Kharif Rice with the Leaf Colour Chart: A Field Trial

Nitrogen is both the largest cost and the largest inefficiency in Indian rice farming: blanket doses applied on a calendar are only partly taken up by the crop, and the rest is lost to volatilisation, leaching and runoff. The Leaf Colour Chart (LCC), developed and promoted in India by ICAR–Indian Institute of Rice Research (IIRR), Hyderabad, offers a field-simple alternative: the newest fully expanded leaves are read against a six-panel chart, and top dressing is applied only when the colour falls below a critical score — each kilogram of N goes where the crop can use it.

This M.Sc (Agri) agronomy thesis tests that logic in a kharif transplanted rice field experiment laid out in a randomised complete block design (RCBD) with three replications at a state agricultural university research station. Treatments compare farmers' practice (recorded from a survey of about 30 farms in the adjoining KVK command area), the state-recommended fixed schedule, LCC-based real-time top dressing at two critical scores and two doses, and a chlorophyll-meter comparison. Observations run from tillering to harvest: growth, yield attributes, grain and straw yield, nitrogen uptake, post-harvest soil status and the nitrogen-use-efficiency indices — agronomic efficiency, recovery efficiency and partial factor productivity — with economics on Agmarknet and minimum-support-price data.

The thesis follows the ICAR PG pattern — Outline of Research Work approved by the advisory committee, field work with progress reports, pre-submission seminar, thesis and viva-voce — and the protocol doubles as a KVK demonstration plot for farmers the same season.

Nitrogen management in transplanted rice in most Indian command areas remains calendar-driven: farmers apply fixed urea splits on fixed dates irrespective of crop demand, variety duration or season, while recommended schedules themselves are fixed at the start of the season. The crop's actual N status is visible in leaf colour, but farmers judge it inconsistently, and neither farmers nor extension staff know how much of the applied N the crop in their own district actually takes up, at what efficiency, and what a real-time method would do to cost and returns. Local, measured evidence comparing farmers' practice, the state-recommended schedule and LCC-based real-time top dressing — on one soil, one variety, one season, with uptake, efficiency indices and real price economics — is missing for most command areas.

This thesis therefore asks: can LCC-based real-time N management, following the ICAR-IIRR protocol, match or improve grain yield while raising nitrogen-use efficiency and net returns relative to the state-recommended fixed schedule and the measured farmers' practice in transplanted kharif rice?

Abstract

Blanket, calendar-based nitrogen application dominates transplanted rice across India, and a large share of the applied N is never taken up by the crop. Real-time N management with the Leaf Colour Chart matches top dressing to the crop's actual leaf colour, which the ICAR–Indian Institute of Rice Research has standardised into a simple protocol. This thesis tests whether LCC-based management improves grain yield, nitrogen-use efficiency and net returns over fixed schedules and farmers' practice in kharif transplanted rice, using an RCBD field experiment at a university research station, a KVK-linked farmers' survey and a demonstration plot.

Introduction

In transplanted kharif rice, leaf colour is a direct window into plant nitrogen status: adequate N means dark green leaves; when the crop runs short, colour fades within days. Farmers eyeball it, but judgement varies from person to person; the chart converts that judgement into a calibrated score. Readings begin 14 days after transplanting and repeat every 7–10 days until flowering; when six or more of the ten newest fully expanded leaves read lighter than the critical score, a fixed top dressing is applied. The method needs no instruments, no lab and no agronomist at the field — which is why it can move from a thesis plot to a farmer field.

Literature gap

LCC-based N management has been evaluated across rice environments and recommended by ICAR institutes, but local validation still matters: the critical score, the top-dress dose and the efficiency gains vary with variety, season, soil and baseline farmer practice. District-level studies that benchmark against a measured farmers' practice rather than an assumed one, report all three standard efficiency indices with uptake data, and carry an economics computation on real market prices are rare — and this combination is what extension staff need before recommending the practice. This thesis supplies that combination for one command area.

Existing practice vs proposed practice

• Existing: blanket N splits on calendar dates regardless of crop demand; rates copied from neighbours; urea applied even when leaves are dark green; no measure of what the crop took up.
• Proposed: weekly LCC readings from 14 DAT; top dressing only when the chart signals shortage, at a fixed dose; the same total-N ceiling as the recommended dose so the comparison isolates timing, not quantity; efficiency, uptake and economics measured on both.

Feasibility

• Land and inputs: an RCBD experiment of six treatments × three replications fits in the plot blocks a university research station allocates to M.Sc theses; seed, fertiliser and labour follow normal station norms.
• Instruments: LCCs, a chlorophyll meter, soil and plant sampling tools, and Kjeldahl digestion in the departmental lab — all standard.
• Time: one kharif season (June–November) covers the field work; the ORW, baseline survey and lab analysis fit the 3rd–4th-semester PG calendar.
• Institutional support: the KVK provides access to the command-area villages for the farmers'-practice survey and hosts the demonstration plot and field day, so the thesis doubles as an extension activity.

In scope

• One kharif season, one medium-duration high-yielding variety, one research-station soil series, transplanted establishment.
• Six N-management treatments in RCBD with three replications; P and K applied uniformly per the recommended dose so the comparison isolates N management.
• Growth, yield-attribute, yield, uptake, NUE, post-harvest soil status and economics observations.
• A baseline farmers'-practice survey (~30 farmers), a demonstration plot and one field day with the KVK.

Out of scope

• Other crops, other establishment methods (direct-seeded, SRI) and multi-season carry-over effects.
• Micronutrients, green-manure and organic-integration treatments.
• Ammonia-volatilisation or leaching-loss measurements (efficiency is inferred from uptake, not gas fluxes).
• Water management treatments; irrigation follows the station's standard schedule for all plots.

Research design: field experiment in a randomised complete block design with three replications. Blocking runs across the known fertility gradient of the site (prior uniformity crop or soil sampling confirms the gradient's direction).

Treatments (example set — replace doses with your state's package of practices and the critical score confirmed for your variety from IIRR recommendations):

A total-N ceiling equal to the recommended dose is imposed on T3–T5 so that the comparison isolates timing, not quantity. P and K are applied uniformly to all plots.

Field protocol: nursery raising and transplanting per station norms; plot size and spacing fixed and recorded; LCC readings begin 14 DAT and repeat every 7–10 days until flowering, taken between 8 and 10 a.m. on cloudless days by the same observer after shade calibration of the eyes; every decision (top dress or skip) is logged plot-wise with the reading and date.

Observations: plant height and tillers/m² at tillering, panicle initiation and flowering; dry matter at the same stages; panicles/m², grains/panicle, filled-grain percentage and 1,000-grain weight at harvest; grain and straw yield from net plots; N content of grain and straw by Kjeldahl for uptake; initial and post-harvest soil samples (available N, P₂O₅, K₂O) analysed by standard methods.

Derived indices: agronomic efficiency (kg grain increase per kg N applied over the nil-N check), recovery efficiency (% of applied N in plant uptake), partial factor productivity (kg grain per kg N applied), cost of cultivation, gross and net returns, B:C ratio using Agmarknet/MSP prices.

Statistical analysis: standard ANOVA for RCBD on every observation; treatment means separated by the least significant difference at 5%; CV reported as the experiment's error check; correlation between LCC scores and SPAD readings; all computation in OPSTAT/SPSS with the raw data appended to the thesis.

The study is a single-season RCBD with a measurement spine that runs from field reading to thesis table. The flowchart below is the plan-of-work diagram for the ORW and the thesis.

flowchart TD
  A["Baseline farmers' practice survey with KVK, ~30 farms"] --> T1["T1: farmers' practice"]
  B["State package of practices"] --> T2["T2: recommended fixed schedule"]
  C["ICAR-IIRR LCC protocol"] --> T3["T3-T5: LCC scores 3 and 4, doses 20 and 30 kg N per ha"]
  C --> T6["T6: SPAD-type meter threshold"]
  T1 --> L["RCBD layout, 3 replications, uniform P and K"]
  T2 --> L
  T3 --> L
  T6 --> L
  L --> W["Weekly LCC readings from 14 DAT, decisions logged plot-wise"]
  W --> D{"6 or more of 10 newest leaves lighter than critical score?"}
  D -->|Yes| TD["Top dress per treatment dose, log date and amount"]
  D -->|No| WK["Re-read after 7-10 days"]
  WK --> D
  TD --> W
  L --> O["Growth, yield attributes, grain and straw yield"]
  O --> U["Kjeldahl N in grain and straw: uptake and NUE indices"]
  L --> S["Initial and post-harvest soil: available N, P and K"]
  O --> E["Economics on Agmarknet and MSP prices"]
  U --> AN["ANOVA for RCBD, LSD at 5 percent, OPSTAT/SPSS"]
  S --> AN
  E --> AN
  AN --> TH["Thesis, pre-submission seminar, KVK field-day report"]

Reading the design

• Controls and comparisons: the nil-N check embedded in the efficiency formulas comes from the station's standard check plot; T1 shows what farmers actually do, T2 what the university recommends, T3–T5 what the chart advises, and T6 what the meter would advise on the same days.
• Error control: blocking absorbs the fertility gradient; fixed plot boundaries, uniform irrigation and single-observer LCC readings keep experimental error low; the CV and LSD tables are the evidence the advisory committee looks for.
• Extension loop: the KVK demonstration plot carries the best-performing LCC treatment so farmers attending the field day see the same protocol that produced the thesis data.

• Repeat over a second kharif season, and extend to boro/rabi rice and direct-seeded establishment where the LCC protocol starts later.
• Add urea super granule or neem-coated urea comparators to test dose–product combinations.
• Integrate the LCC protocol with leaf-colour-based mobile decision aids and test their agreement with the chart.
• Scale the KVK demonstration into a cluster of villages with a before–after adoption study on dose and number of top dressings.
• Add ammonia-volatilisation measurement for a fuller efficiency picture in collaboration with a soil-physics lab.