1: Nitrogen optimization in Rice

Nitrogen in the plant is a very important subject. Nitrogen plays an important part in many essential functions and compounds necessary for plant life and growth. Nitrogen may be found in various parts of the plant in different forms. There is nitrogen in the leaves, grain, plant tissue and roots of plants. Nitrogen may function as part of the plant structure or be involved in the life processes.

• Nitrogen makes up part of the chlorophyll in plants. Chlorophyll is the green part of leaves and stems. Light energy is taken by the chlorophyll and used to make sugars for the plant.

• Nitrogen is an important part of the compounds that regulate plant growth and development. Nitrogen is also an important part of the plant structure.

• Nitrogen is used to make protein by the plants. Protein is stored in the grain, fruit and seeds of plants.

• In the roots, nitrogen is found in proteins and enzymes. They help the nutrients and water be taken up into the plant.

Impact of nitrogen deficiency:

Plants that are deficient in nitrogen have stunted growth, depending on the severity of the deficiency. Leaf growth is inhibited; younger leaves are inhibited in particular. Longitudinal shoot growth is inhibited, as is the increase in thickness. Deficient plants often become pale green to yellowish-green due to inhibited chloroplast and chlorophyll synthesis. Leaves start to wither and dry out, turning yellowish brown to brown.

Impact of excess nitrogen?

• Excess nitrogen can’t be taken up by plants, thus the excess amount of nitrogen is wasted and farmer’s expenditure increases. Cutting down amount of nitrogen fertilizers can reduce farmer’s input cost, without affecting the yield, increase farmer’s profitability.

• Some soil microorganismcan transform nitrogen provided in fertilizers into nitrogen containing gases. Excess amount of nitrogen (not absorbed by plant) available in the soil will transform into nitrogen containing gases, that get released into the atmosphere like the GHG.

Anticipated yield response when managing for a certain N balance

• 100kg of fertilizer, estimates plant uptake is 80, N balance = +20 

• Target +30kg balance which provides a safe buffer; farmer unlikely to see yield reduction

• There is opportunity to reduce N fertilizer by 20 kg per hectare without impacting the yield

2: Usage and utility of leaf color chart

What is a Leaf Color Chart?

• A simple, easy to use & inexpensive tool

• It helps farmers to determine the right time of N application

• It is done by measuring leaf color intensity which is related to leaf N status

LCC is an ideal tool to optimize N use at reasonably high yield levels, irrespective of the source of N applied

Main features of LCC

• Made of high impact plastic or high quality plastic

• Consists of six shades: light yellowish green (No.1) to dark green (No. 6) 

• Color strips are fabricated with veins resembling rice leaves.

How to use the LCC

• Start LCC readings from 14 DAT (Days after Transplantation) or 21 DAS (Days after sowing)

• The last reading is taken when the crop just starts to flower. 

• Randomly select at least 10 disease-free rice plants or hills in a field with uniform plant population from different areas of the plot.

• Select the topmost fully expanded leaf from each hill or plant

• Place the middle part of the leaf on a chart and compare the leaf color with LCC shades

• Do not detach or destroy the leaf

• Measure the leaf color under the shade of your body, because direct sunlight affects leaf color readings  

• If possible, the same person should take LCC readings at the same time of the day every time

• If more than five leaves read below a set critical value, apply

  • 23 kg N ha^-1 (one 50-kg bag of urea/ha) for wet season

• The suggested critical values are:

  • 4 for transplanted rice (TPR)

  • 3 for high-density wet-seeded rice (WSR)

• Repeat the process at 7 to 10 day intervals or at critical growth stages (early tillering, active tillering, panicle initiation, and first flowering) and apply N as needed.

Utility of LCC:

LCC is a guide for application of fertilizer N to maintain an optimal leaf N content. It helps farmers to apply optimum amount of Nitrogen fertilizers, resulting in lesser wastage, lesser input cost with sustainable yield of paddy. 

3: Early transplantation of paddy

Introduction:

Rice crops can be either direct seeded or transplanted. In direct seeding, seeds are sown directly in the field. While in transplanting, seedlings are first raised in seedbeds before they are planted in the field.

Timely planting into a well prepared seedbed will help produce a fast growing, uniform crop that will have higher yields and better competition against weeds and other pests.

Why it is important?

Timely crop planting increases crop productivity by

• Mitigating risks of yield losses caused by extreme weather conditions such as extreme cold/extreme heat, flood condition, draught condition etc.

• Efficient use of resource

• Providing enough space for timely sowing of wheat, as there is potential for 50% loss in production in wheat because of late planting

• Late transplantation is prone to more bacterial blight & increased attack by insect pests.

• High temperature at the stage of grain filling may produce empty spikelet.

When to transplant:

• The ideal transplanting date for paddy is between June 15 to July 15 to get the optimum yield possible

• Proper and timely nursery is important for timely transplantation of paddy

• Nursery timing: 2 weeks prior to the planned date of transplantation

• The delayed nursery transplanted seedlings produce low and weak tillering reducing final yield.

4: Nursery raising

Why Nursery is important?

Transplantation of healthy, vigorous nursery seedlings without insect pests gives better yield. The delayed nursery seedlings produce low and weak plants reducing the final yield. It is very important to raise rice nursery and transplant it at an appropriate time to get optimum yield. Late nursery raising leads to late transplantation of paddy crop that is prone to more bacterial blight & increased attack by insect pests, beside, high temperature at the stage of grain filling may produce empty spikelet.

Types of nursery:

 Two main types of nurseries are wet bed nursery and dry bed nursery.

Wet bed nursery:

• Seed & seedbed area: 50 kg seed & 500 m² seedbed area for TP one ha of main field

• Locate the seedbed in a fertile field that is easy to irrigate & drain

• Start preparing the seedbed 2 weeks before planting time

• Add organic manures and/or fertilizers as needed

• Irrigate, plow, puddle and level the field

• Prepare beds of 1 to 1.5 m width, 4-5 cm height & any convenient length

• Pre-germinate the seeds 2 days before sowing: 24 h soaking & 24 h incubation

• Sow the pre-germinated seeds on beds

• Water the seedbed 2-3 DAS and then maintain a water level of 2-5 cm, depending on the height of seedlings

• Apply 20-40 g urea or DAP per m² at 10 DAS, if needed

• Apply pesticide only when needed

• Seedlings are ready for TP from 15-20 DAS 

Dry bed nursery:

• Compute the seed & seedbed area: 50 kg seed & 500 m² seedbed area for TP one ha of main field

• Locate the seedbed away from electric light in a fertile field with light soil and easy access to a water source

• Start preparing the seedbed 2 weeks before planting time

• Add enough organic manures &/or fertilizers

• Plow and harrow the field

• Prepare raised seedbeds of 1.5 m width, 0.1-0.15 m height, and any convenient length

• Seed priming: weigh required quantity of clean seed, soak for 24 h and then dry in the shade

• Primed seed is reported to germinate faster than fresh dry seed

• Sow the primed seeds on raised beds & cover the seed lightly with soil or rice hull

• Water the seedbed till saturation after sowing

• Then water the bed periodically as seedlings emerge & grow

• Regulate the water supply, if necessary, to control the rate of seedling growth

• Apply pesticides to control pests, if needed

• Seedling are ready from 20-25 DAS

Transplanting: Critical Factors

• Proper nursery management

• Careful handling of young seedlings for fast revival and early growth after TP

• Shallow transplanting at 1-2 cm depth

• Optimum plant-to-plant spacing: 20 x 20 cm to 25 x 25 cm

• Optimum number of seedlings: 1-2 per hill