IMPORTANCE OF WATER MANAGEMENT IN CROP PRODUCTION

Water is one of the most important inputs essential for the production of crops. Plants need it continuously during their life and in huge quantities. It profoundly influences photosynthesis, respiration, absorption, translocation and utilization of mineral nutrients, and cell division besides some other processes. Both its shortage and excess affects the growth and development of a plant directly and, consequently, its yield and quality. Rainfall is the cheapest source of natural water-supply for crop plants. In India, however, rainfall is notoriously capricious, causing floods and droughts alternately. Its frequency distribution and amount are not in accordance with the needs of the crops. Artificial water-supply through irrigation on one occasion, and removal of excess water through drainage on another occasion, therefore, become imperative, if thecrops are to be raised successfully. Water management in India, thus, comprises irrigation or drainage or both, depending considerably on the environmental conditions, soil, crops, and climate. It is a situation-oriented entity.

Water effects the performance of crops not only directly but also indirectly by influencing the availability of other nutrients, the timing of cultural operations, etc. Water and other production inputs interact with one another. In proper combinations, the crop yields can be boosted manifold under irrigated agriculture.

Water is a costly input when canals supply it. The constructing of dams and reservoirs, the conveying of water from storage points to the fields, the operating and the maintaining of canal systems involve huge expense. The misuse of water leads to the problems of water-logging, salt-imbalance, etc., thus rendering agricultural lands unproductive. Hence a proper appreciation of the relationship among soils, crops, climate and water resources for maximum crop production.

Water resources. Taking the total geographical area of the country at 328 million hectares and the average annual rainfall at about 112 cm, the total annual precipitation in the country is estimated at about 3,700,000 million cubic meters. The south-westerly monsoon contributes over 80 per cent to the total precipitation in the country. The Central Water and Power Commission, New Delhi, has estimated that of the total annual precipitation amounting to 800,000 million cubic meters seeps into the ground, about 1,700,000 million cubic meters flows into the rivers and the remaining amount of about 1,200,000 million cubic meters evaporates back into the atmosphere.

The water, flowing on the surface and that seeping into the ground, forms the two major sources of water for irrigating crops.

Surface-Water Resources. A large number of rivers of various potentials and discharges are spread all over the country. The rivers in the north, which originate from the Himalayas, are snow-fed and, thus, have less seasonal fluctuations in their flow than the rivers in the other parts of the country. The flow in the rivers of the central and southern parts of the country depends entirely on the monsoon. The rivers flow to the full during the rainy season (July to September) and their flow dwindles with the approach of the summer.

The surface-flowing water needs to be trapped in ponds, tanks, lakes or artificial reservoirs when it is available in abundance so that it can be fruitfully used for irrigation during the rainless period to meet the water needs of crops. Of the annual surface flow of 1,700,000 million cubic meters, only about 666,000 million cubic meters can be utilized for the purpose of irrigation owing to the physiographical limitations.

Ground-Water Sources. Substantial supplies are also available from ground-water sources. Of the 800,000 million cubic meters of rain-water that seeps into the ground annually, about 430,000 million cubic meters of it is absorbed by the surface layers of the earth's crust and, thus, can be utilized directly by the vegetation in the process of evapo-transpiration and growth. The remaining 370,000 million cubic meters of rain-water percolates deep into the porous strata of the earth's crust, representing the gross annual enrichment of the underground water. This ground-water is tapped by digging or drilling shallow or deep wells and is lifted by using mechanical devices for irrigating thecrops.

A precise quantitative inventory regarding the ground-water reserves is not available. Organization such as the Geographical Survey of India, the Central Ground-Water Board and the State Tube-Wells and the Ground-Water Boards are engaged in this task. It has been estimated by the Central Ground-Water Board that the total ground water reserves are on the order of 55,000,000 million cubic meters out of which 425,740 million cubic meters have been assessed as the annual recharge from rain and canal seepage. The Task Force on Ground-Water Reserves of the Planning Commission has also endorsed these estimates. All recharge to the ground-water is not available for withdrawal, since part of it is lost as sub-surface flow. After accounting from these losses, the gross available ground-water recharge is about 269,960 million cubic meters per annum. A part of this recharge (2,460 million cubic meters) is in the saline regions of the country and is unsuitable for use in agriculture owing to its poor quality. The net recharge available for ground-water development in India, therefore, is of the magnitude of about 267,500 million cubic meters per annum. The Working Group of the Planning Commission Task Force Ground-Water Reserves estimated that the usable ground-water potential would be only 75 to 80 per cent of the net ground-water recharge available and recommended a figure of 203,600 million cubic meters per annum as the long-term potential for ground-water development in India.

IRRIGATION DEVELOPMENT AND POTENTIAL IN INDIA

Irrigation has been practiced in India since time immemorial. Wells and tanks, as known today's as 'minor irrigation works', were constructed by several kings of ancient times for public welfare. Significant development irrigation, however, can be stated to have commenced from 1850 onwards, with large-scale or major irrigation projects. These activities have been further accelerated after Independence in 1947. Today, India has about 34 million hectares of land under irrigation and this amounts to about one-fifth of the total cultivated area. Source-wise, crop-wise and state-wise irrigated areas in the country are shown in Tables 1,2 and 3. Major irrigation projects, irrigating more than 0.10 million hectares, have been listed in Table 4.

With utilization water resources, both from the surface flows and from the ground-water recharge, the Second Irrigation Commission has calculated that the ultimate area that can be irrigated is of the order of about 82 million hectares in the country. Till the end of the Fourth Plan, about 45 per cent of the surface utilizable flow and about 20 per cent of the usable ground-water was proposed to be utilized to irrigate about 34 million hectares.

Table 1. Net area irrigated from different sources in 1970-71

State/Union Territory	Government Canals	Private Canals	Tanks	Wells	Other Sources	Total
					(Thousand ha)
1. Andhra Pradesh	1,579	-	1,112	509	113	3,313
2. Assam	71	291	-	-	210	572
3. Bihar	812	2	169	551	626	2,160
4. Gujarat	204	3	30	945	10	1,209
5. Haryana	951	-	1	575	5	1,532
6. Himachal Pradesh	-	-	-	1	90	91
7. Jammu and Kashmir	62	210	-	1	6	279
8. Karnataka	419	2	365	259	92	1,137
9. Kerala	201	10	13	5	142	431
10. Madhya Pradesh	709		130	562	78	1,480
11. Maharashtra	280/font>	32	225	821	69	1,427
12. Manipur	-	-	-	-	65	65
13. Meghalaya	-	-	-	-	37	37
14. Nagaland	-	-	-	-	12	12
15. Orissa	231	32	583	45	258	1,1479
16. Punjab	1,286	6	-	1,591	5	2,888
17. Rajasthan	756	-	270	1,083	23	2,132
18. Tamil Nadu	883	1	898	774	36	2,592
19. Tripura	-	-	-	-	22	22
20. Uttar Pradesh	2,497	1	371	17	209	1,489
21. West Bengal	629	331	303	17	209	1,489
22. Andaman and Nicobar Islands	-	-	-	-	-	-
23. Arunchal Pradesh	-	-	-	-	-	-
24. Dadra and Nagar Haveli	-	-	-	-	-	-
25. Delhi	14	-	1	34	-	49
26. Goa, Daman and Diu	-	-	-	-	8	8
27. Laccadive, Minicoy and Amnidivi Islands	-	-	-	-	-	-
28. Mizoram	-	-	1	-	1	2
29. Pondicherry	11	-	6	10	-	27
India (Total)	11,594	923	4,537	11,864	2,404	31,292
Relative area irrigated from different sources as percentage	37.1	2.9	14.5	37.8	7.7	100

Table 2. Crop-wise gross irrigated area in 1970-71

Crop	Total Area	Irrigated Area	% irrigated area	Relative area in percentage of the total irrigated area
			(Thousand ha)
Rice	37,387	14,917	49.9	38.7
Sorghum	16,994	626	3.7	1.6
Pearl-millet orbajra	13,192	514	3.9	1.3
Maize	5,836	925	15.8	2.4
Crowfoot millet	2,525	334	1.3	0.9
Wheat	18,139	9,829	54.2	25.5
Barley	2,558	1,328	51.9	3.4
Gram	7,847	1,224	15.6	3.2
Pigeon-pea	2,652	12	0.5	0.03
Sugarcane	2,650	1,929	72.8	5.0
Spices and condiments	1,873	660	35.2	1.7
Fruits and vegetables	3,598	956	26.6	2.5
Groundnut	7,480	378	5.1	1.0
Sesamum	1,874	44	2.3	0.1
Rape and mustard	1,400	321	22.9	0.8
Lineseed	1,203	17	14.1	0.04
Cotton	7,886	1,287	16.3	3.3
Fodder crops	7,385	1,347	18.2	3.5
Tobacco	448	101	22.5	0.3
Other crops	37,534	4,498	12.0	12.0
Grand Total (gross area sown)	167,412	38,552	23.0	100
Net Area Sown	141,161	31,292	22.2	81.1
Area Sown more than Once	26,251	7,260	0.8	18.9

Table 3. State-wise sown and irrigated area in 1970-71

State/Union Territory		New Area				Gross Area
	Sown	Irrigated	Percentage		Sown	Irrigated	Percentage
						(Thousand ha)
1. Andhra Pradesh	11,735	3,313	28.2		13,347	4,233	31.6
2. Assam	2,226	572	25.7		2,773	572	20.6
3. Bihar	8,454	2,160	25.6		11,026	2,732	24.8
4. Gujarat	9,428	1,209	12.8		10,045	1,307	13.0
5. Haryana	3,565	1,532	43.0		4,957	2,230	45.0
6. Himachal Pradesh	544	91	16.7		911	156	17.1
7. Jammu and Kashmir	706	279	39.5		866	330	38.1
8. Karnataka	10,248	1,137	11.1		10,887	1,355	12.4
9. Kerala	2,172	431	19.8		2,933	601	20.5
10. Madhya Pradesh	18,352	1,480	8.1		20,562	1,523	7.4
11. Maharashtra	18,304	1,427	7.8		19,304	1,656	7.4
12. Manipur	179	65	36.3		188	75	39.9
13. Meghalaya	163	37	22.7		195	37	19.0
14. Nagaland	100	12	12.0		102	12	11.8
15. Orissa	6,119	1,149	18.8		8,440	1,624	19.2
16. Punjab	4,053	2,888	71.3		5,678	4,243	74.7
17. Rajasthan	15,179	2,132	14.0		16,729	4,253	14.7
18. Tamil Nadu	6,169	2,592	42.0		7,384	3,410	46.2
19. Tripura	240	22	9.2		345	22	6.4
20. Uttar Pradesh	17,305	7,190	41.5		23,207	8,344	36.0
21. West Bengal	5,542	1,489	26.9		7,092	1,541	21.7
22. Andaman and Nicobar Islands	18	-	-		18	-	-
23. Arunchal Pradesh	56	-	-		56	-	-
24. Dadra and Nagar Haveli	16	-	-		17	-	-
25. Delhi	81	48	59.3		117	56	47.9
26. Goa, Daman and Diu	133	8	6.0		139	8	5.8
27. Laccadive, Minicoy and Amnidivi Islands	3	-	-		3	-	-
28. Mizoram	39	2	5.1		40	2	5.0
29. Pondicherry	32	27	84.4		51	40	78.4
All-India	141,161	31,292	22.2		167,412	38,552	23.0

Table 4. Important Irrigation projects in India

State		Name of Project		Irrigated Area (Million ha)
		During 1850 to 1950
Andhra Pradesh		Godavari Delta System		0.35
Andhra Pradesh		Krishna Delta System		0.60
Bihar		Sone Canal		0.24
Punjab		Western Jamuna		0.52
Punjab		Sirhind Canal (Sutlej)		0.95
Punjab		Upper Bari Duab Canal (Beas)		0.40
Rajasthan		Ganga Canal (Sutlej)		0.22
Uttar Pradesh		Upper Ganga Canal		0.80
Uttar Pradesh		Lower Ganga Canal		0.60
Uttar Pradesh		Sarda Canal		0.80
Uttar Pradesh		Agra Canal (Jamuna)		0.18
		After 1950
Andhra Pradesh		Krishna Delta System		0.60
Andhra Pradesh		Nagarjunasagar (Krishna)		0.81
Andhra Pradesh		Pochampad (Godavari)		0.23
Bihar		Gandak		1.31
Bihar		Sone Barrage		0.12
Gujarat		Kakrapara (Tapti)		0.23
Gujarat		Mahi Right Bank Canal		0.19
Gujarat		Narmada		0.40
Gujarat		Ukai (Tapti)		1.60
Madhya Pradesh		Gandhisagar (Chambal)		0.45
Bihar		Sone Barrage		0.12
Madhya Pradesh		Kotah Barrage (Chambal)		0.57
Madhya Pradesh		Rana Pratap Sagar (Chambal)		0.40
Madhya Pradesh		Tawa		0.32
Maharashtra		Bhima		0.12
Maharashtra		Jayakwadi (Godavari)		0.14
Kerala		Kallada		0.11
Karnataka		Ghataprabha		0.20
Karnataka		Malaprabha		0.12
Karnataka		Tungabhadra		0.41
Orissa		Hirakud (Mahanadi)		0.24
Orissa		Mahanadi Delta		0.65
Punjab		Beas Dam		3.24
Punjab		Bhakra Nangal (Sutlej)		1.23
Rajasthan		Rajasthan Canal (Sutlej)		1.06
Uttar Pradesh		Matatila (Betwa)		0.17
Uttar Pradesh		Ramaganga		0.69
West Bengal		Kanasbati Reservoir		0.38
West Bengal		Mayurashi		0.25
West Bengal		Damodar Valley		0.42
West Bengal		Durgapur Barrage (Damodar)		0.42

The programs for modifying weather, the desalinization of sea-water and the National Water Grid, if enforced, will further increase the potential for irrigation manifold.

Surface water for irrigation is obtained from flowing rivers, and from tanks, ponds, lakes or artificial reservoirs. The flows of rivers are directly diverted into canals, or high dams are built across the river to form first large canals for irrigation. The future development of irrigation aims at impounding the surplus flows of rivers by constructing dams for use during the dry periods.

Water from all these sources is conveyed to the field through lined or unlined canals, distributaries and minors through the final structure called outlet. All this conveyance system up to the outlet is built by the Irrigation Departments. From the outlet, water flows into small water-courses which are constructed, owned and managed by a group of farmers. During its conveyance, there are considerable losses through seepage, percolation and evaporation. From a typical water-distributary system, the losses in the main canal vary from 10 to 15 per cent, and in the water-courses from 15 to 30 per cent. Thus the total losses from the source till the water reaches the farmers' fields may amount to 40-60 per cent.

Ground-water is tapped by digging shallow and large diameter percolation wells or drilling deep tube-wells and lifting it to the surface. Shallow wells derive their water-supply from the surrounding area through seepage, percolation, high-water table, etc. the deep wells depend for their water on aquifers, which may have their source at some distance. River valleys, canal-irrigated areas, low-lying places, natural vegetation and trees growing luxuriantly are indications of the presence of ground-water resources. The rate at which the water can be pumped out from a well depends upon recharging rate which, in turn, depends upon the permeability of the surrounding area in the case of shallow wells and on the thickness and the magnitude of aquifers.

Utilization of water resources. The scientific utilization of water resources for crop production involves the consideration of the suitability of land and water for irrigation and then planning of crops and water-management practices commensurate with them. Water-management practices include irrigation and drainage. Irrigation comprises three fundamentals: how much to drain, how best to drain and how rapidly to drain under a given situation of soil, water, and crops. These problems are discussed in this chapter.