Manuring

It is important to ensure adequate replenishment of nutrients in the soil removed by harvest. A series of field experiments conducted under different agro climatic conditions of Northeast (N.E.) India have recorded response not only to N but also to annual application of P and K. The response curves obtained from these experiments have indicated that annual application of balanced dose of NPK is required to harvest maximum crop. Results have shown that for sustaining a crop of 2300 kg made tea per hectare (KMTH) in different regions, in general, a dose of nitrogen not exceeding 140 kg, phosphate 20-50 kg and potash not exceeding 140 kg would suffice. Survey data from a large number of tea estates also corroborated these results and in 80% of the surveyed gardens, this NPK dose was found to be optimum for producing 2500-3000 KMTH. The possibility of sustaining a productivity level of 3500 KMTH or more by marginal increase of N over 165 kg along with 50 kg phosphate and 165 kg potash was also indicated from the data. The current recommendation on manuring is based on a number of trials conducted at Tocklai and a commercial tea estates of Northeast India.

Recommendation on NPK manuring in mature tea for plain districts of N. E.India

Yield range in KMTH (cycle average)
N
kg/ha
P2O5
kg/ha
K2O kg/ha
Soil available potash status
Low

(< 60 ppm)
Medium
(60-100 ppm)
High
(> 100 ppm)
Up to 1500
Up to 90
20
Up to 90
Up to 70
Up to 50
1500-2000
90-110
20-30
90-110
70-80
50-70
2000-2500
110-140
30-50
110-140
80-120
70-100
2500-3000
140-165
50
140-165
120-140
100-120
           

In the Darjeeling hills, the agro climatic conditions are different from those of plains. The cool temperature slows down the organic matter decomposition and the productivity levels are lower as compared to the plain districts. Therefore, the N levels should not exceed 110-120 kg/ha. The manuring schedule recommended for Darjeeling is shown in the table below:

Recommendation on NPK manuring in mature tea in Darjeeling

Yield range in KMTH (cycle average)
N
kg/ha

P2O5
kg/ha

K2O kg/ha

Soil available potash status
Low
(< 60 ppm)
Medium
(60-100 ppm)
High
(> 100 ppm)
Up to 600
Up to 60
20
Up to 60
Up to 50
Up to 35
600-1000
60-90
20
60-90
50-70
35-50
1000-1400
90-120
20
90-120
70-100
50-70
           

Time of manuring

Fertilizers should be applied only when the tea bushes are ready to utilize them. As a general rule, the best time for fertilizer application is after the first rain in spring has moistened the soil to a depth of 45 cm and there is some new growth in case of unpruned tea. In case of pruned and skiffed teas, the fertilizers should be applied after the bushes have produced two new leaves. A weed free clean ground is desirable at the time of manuring.

Method of Manuring

In the mature tea, after complete coverage of ground, fertilizers are applied uniformly on the ground as broadcast. In the hills of Darjeeling and other areas, fertilizers should be applied in a half circular band on the up slope keeping a distance from the collar.

It is recommended to apply N and K fertilizers in two splits if the dose exceeds 100 kg/ha. This will ensure adequate supply of nutrients throughout the growing period and higher utilization efficiency. The 60% of the dose of N and K should be applied in March-April (1st split) and the second split (i.e. the remaining 40%) should be applied in August-September. The entire quantity of phosphatic fertilizer should be applied in the beginning of the season along with first split of N and K. In very light texture soil, the number of splits may be increased.

Sulphur

The tea soils of Northeast India also were depleted of sulphur to different extent due to replacement of SOA by urea for quite sometime. Studies showed that soil application of sulphur @ 20-45 kg/ha improves yield and quality of tea. The current recommendation is that sulphur should be applied at 20 kg S/ha only if the soil test indicates values lower than the critical limit (40 ppm available sulphur). It can be applied to well drain tea fields as broadcast along with the NPK fertilizers in spring. Studies have also shown that available sulphur is correlated with high organic matter and response in the Dooars has not been consistent.

Micronutrients

Among various micronutrients tried only zinc has shown consistent response and is recommended particularly in unpruned / skiffed teas. Foliar application of zinc sulphate at 1-2% concentrations (w/v) has been found beneficial and produced up to an average of 10% increase in yield. The present recommendation is not to exceed 12.5 kg zinc sulphate per hectare per year, which is to be applied in 4-6 sprays (1-2% concentrations) in early (March onwards; 2-3 sprays) and late season (September onwards; 2-3 sprays). Indiscriminate use of zinc sulphate sprays should be avoided as it may lead to high levels in made tea. Foliar application of manganese, boron and molybdenum has shown varied responses and are at present not recommended as a regular practice.

Foliar nutrition

Foliar nutrition is beneficial under stress condition or coinciding with physiological changes in the bush. NPK mixture 2-1-2 or 2-1-3 where potash status is low, @ 0.5-1 percent can be sprayed during this period.

Foliar sprays of potash @ 1% MOP (w/v) during moisture stress period can enhance the water use efficiency of the bushes. MOP (1%) and MgSO4 (1%) sprays from Jan to March help ameliorate the ill effect of moisture stress in UP teas.