Plant nutrient mining in North-Eastern India

Plant nutrient mining in North-Eastern India is bringing down crop yield levels. The North-Eastern Hills region of India with geographical area of 18,381 sq. km. has 6.3 percent of its area under cultivation. There is a wide gap between plant nutrient removal by crops and nutrient replenishment in this region. Average replenishment of N, P₂O₅ and K₂O, both from organic and mineral sources, is below 27 kg/ha whereas depletion/removal by crops of these nutrients is more than 120 kg/ha, annually. This problem needs immediate attention because low fertility status of these soils is becoming a serious constraint, limiting crop production. All states of the region are deficient in food grains and this deficiency gap will widen if improvement of soil fertility is further ignored.
Rice is the most important crop of the region and covers about 65.8 percent of cultivated area under annual crops. Other cereals, pulses and oilseeds account for 11, 3.3 and 5.9 percent of the cultivated area, respectively. Average yields of rice, maize, wheat, pulses and oilseeds in the region is 1.59, 1.27, 1.78, 0.82 and 0.83 tonnes/ha, respectively. Among fruit crops, apple, peach, pear, citrus and pineapple are of major importance.

The entire soils of Meghalaya, Tripura, Manipur and Arunachal Pradesh and over 50 percent of soils of Nagaland and Sikkim are deficient in P. The soils of the region are, by and large, acidic in reaction and P is fixed immediately after application. It has been observed that up to 99 percent of applied P became fixed in some soils. Available K is high in alpine and sub-alpine zones, low in mid-tropical plains and medium in the other three agro-climatic zones.

Nutrient addition through mineral and organic sources and nutrient balance in North-Eastern India (‘000 tonnes).

Zone	Nutrients added									Nutrient balance
	N			P2O5			K2O			N	P2O5	K2O
	I	O	T	I	O	T	I	O	T
Sub-alpine	0.21	0.11	0.32	0.08	0.03	0.11	0.05	0.06	0.11	-7.9	-1.7	-6.5
Sub-tropical hills	2.26	1.42	3.68	0.56	0.35	0.91	0.19	1.22	1.41	-14.8	-2.5	-15.3
Sub-tropical plains	2.07	0.63	2.70	0.32	0.20	0.52	0.31	0.41	0.72	- 3.1	-0.3	-4.8
Mild-tropical hills	4.03	1.67	5.70	0.84	0.53	1.37	0.21	1.26	1.47	-16.4	-2.5	-18.0
Mild-tropical plains	10.21	2.81	13.02	3.42	0.89	4.31	2.11	2.14	4.25	-28.6	-3.1	-31.6
Total	18.78	6.64	25.42	5.22	2.00	7.22	2.87	5.09	7.96	-70.8	-10.1	-76.1

I: Inorganic sources; O: Organic sources: T: Total
Source: Sharma, U.C. and L. M. Shukla (2001), Fertiliser News, 46(4), pp. 115-119.

It is evident that use of K₂O is very low and needs to be augmented adequately to reduce fast depletion of this plant nutrient in the soil. For balanced use of N, P and K, it is necessary to take a fresh look at the ratio of the present plant nutrient use and enhance their use from fertilizers in a proper ratio. Unless immediate corrective measures are taken crop production will further decrease, as the soils will not be able to provide adequate nutrition for growing crops. This has major long term implications for the sustainability of agriculture in these states.