In this article we will discuss about the Khadin system of water harvesting used in Western Rajhasthan, India.
In the past, many dryland areas around the world have been considered as ‘wastelands’ because of their low soil organic carbon, poor water availability and frequent occurrence of droughts due to erratic and scanty rainfall which has resulted in low crop productivity.
Though the water availability for irrigation has increased multi-fold in some parts of Rajasthan due to Indira Gandhi Nahar Program, land available for expansion of agricultural area is limited and therefore, it is essential to formulate ideal management strategies to optimise the water use efficiency and to increase crop productivity potential of less productive soils from the drylands.
Since 15th century, people of extremely dry Western Rajasthan around Jaisalmer region follows a traditional runoff farming, a typical land use system widely prevalent in highly arid areas of Thar desert which is commonly known as khadin cultivation in which rainwater harvested in the lower reaches during kharif is used for rabi crops cultivation.
The khadin system consists of embankment built across the drainage line that collects rainfall and sediments from surrounding catchment areas. Sluices and spillways are constructed to drain away excess water. It helps in recharge of groundwater apart from enabling growing kharif and rabi crops depending upon the amount of rainfall and consequent runoff. However, the crop productivity of khadin cultivation remains low due to edapho-climatic constraints including nutrients deficiency, salt encrustation, sodicity and water logging.
The impact of weather extremes especially droughts has often resulted in low food production that has led to malnutrition and other related complications. Where the regions receive annual rainfall of less than 150 mm, it is difficult to cultivate even a single crop. Therefore, people used their traditional wisdom to devise their own strategies to collect and store runoff water from rainfall events, for some assured harvest to meet their livelihood.
However, for devising an ideal khadin, knowledge of salient factors is essential, e.g. intensity and distribution of rainfall, topography and terrain conditions, soil type and quality, socio-economic conditions of the people are the prerequisite. Besides, it is also imerative to evaluate the environmental, ecological and economic implications prior to the construction of khadins.
Khadin System of Western Rajasthan:
1. Factors to Evaluate the Suitability of Khadin:
Assuming about 60% annual rainfall, the ratio between cultivated and catchment area varies from 1:12 to 1:15 but to practice efficient agriculture a minimum of at least 1:15 area is required. To decide the ideal location for khadins, knowledge on the landscape is essential. Besides, the information on intensity and distribution of rainfall, number of rainfall events, frequency distribution of varied intensity storms, vegetation types and density, topography, landform along with slope gradient and relief variations, soil types, surface and subsurface texture, soil depth, soil hydraulic conductivity, evaporation, runoff intensity are also required.
Moreover, it is also important to understand the socio-economic conditions of local farmers for the effective implementation of any water harvesting programme in participatory approach. Environmental and ecological impacts on runoff water harvesting also need to be assessed as the arid region are highly fragile and have a limited capacity to adjust to change.
2. Location, Climate and Physiography:
Thar Desert covers an area of 44.6 million hectare, out of which 27.8 million hectares lie in India and the rest in Pakistan. Arid Rajasthan includes a major part of the Thar Desert of India. It covers 12 per cent of the country’s total geographical area (TGA), of which 62 per cent falls in western part of Rajasthan. The eastern limit of the arid Rajasthan lies roughly along the 500 mm isohyet which is almost coterminous with the moisture availability index or also called the aridity index of -66.6.
The study area is an arid and desert region of Jaisalmer in Rajasthan of northwest India. This region is characterized by highly variable and low annual precipitation (100-300 mm), extremes of temperatures (-3 to 48°C), high wind speed (8-9 ms-1), and long sunshine hours (~ 9.4 h d-1) which characterize a very large evaporative demand. Because of poor rainfall, soil moisture stress is an impediment to vegetation growth.
The soils are loose, sandy to sandy loamy with excess permeability of greater than 25.4 cm h -1. Rainfall is received during a short duration from southwest monsoon with about 15 rainfall events and the supply of moisture lasts for a limited period of 90 days only. Low humidity, combined with strong wind regime, leads to advection, a phenomenon that causes evaporation loss more than the energy actually available through solar radiation.
3. Soil Characteristics of Khadin and their Problems:
Pedons were morphometrically examined from the upper and lower reaches along two soil transect of a runoff farming system (khadin) at the Bharamsar village (27o01’16.5″ N latitude, 70°52’42” E longitude,) which was considered for the investigation. The results indicate that the soils are moderately shallow in depth (<50 cm) in upper reaches to very deep (>150 cm) in the lower reaches. Soil texture becomes heavier from sandy loam in upper and middle reaches to sandy clay loam/sandy clay in lower reaches indicating increase in the intensity of pedogenic activity from upper to lower reaches.
The pH of the soils is mild to moderately alkaline (>8) and it increases from upper reaches to lower reaches. Electrical conductivity of the soil saturation extract (ECe) is found to be lower in the soils of lower reaches (0.28 to 1.40 dSm-1) as compared to that in the middle (2.2 to 5.8 dSm-1) and upper reaches. Soils are highly calcareous and the structure varies from massive, soft to coarse moderately hard and sub- angular blocky.
The surface soils of 70 per cent of the total geographical area were generally saline-sodic and sodic with exchangeable sodium percent (ESP) values of more than 15 and ECe was more than 4 dSm-1. Soil organic carbon (SOC) was found to be low and varied from 0.02 to 0.23 per cent. High amount of exchangeable sodium was observed throughout the depth in the soils of pedons studied from all the reaches.
a. Poor Soil Quality:
In Bharamsar khadin, soils are generally saline-sodic and sodic with ESP of more than 15 and ECe of more than 4 dSm-1 in the 70 per cent of the total geographical area (TGA) of the surface soils, and sub-soil sodicity and salt encrustations were observed in many places of khadin. Arid environments and excessive evaporation caused a progressive formation of pedogenic calcium carbonates (PC) with the concomitant increase in Na+ ions in soil solution.
This facilitated the translocation of Na-clay in the soil profile resulted in the increase in pH, decrease in Ca/Mg ratio of exchange sites with depth and finally in the development of subsoil sodicity. The gypsum requirement was calculated based on ESP and cation exchange capacity of the soils and for the reclamation of 60 per cent of the sodium in the top 15 cm of the soils, between 2000-2200 kg of gypsum per hectare was advocated except for the soils in the western portion of lower reaches where the ESP in the upper 50 cm of soils were less than 4. Siltation was one of the major problem observed in the soils of Roopsi khadin of the study area. The siltation restricts groundwater percolation and accelerates waterlogging.
b. Nutrient Deficiency:
Since the nutrient availability in soils is important to ensure the optimum yield, information on their content and distribution are essential for any sustainable land use planning especially in the highly arid ecosystem as the dryland soils suffer multinutrient deficiencies in many States of Indian semi-arid tropics.
Therefore, in the present case study, macronutrient cations availability such as phosphorous (P) and potassium (K) from the soils of khadin in Baramshar, Jaisalmer district and nitrogen (N), P, K from the soils of khadin near Bambore-Baoroli in Jodhpur district were analysed using standard procedures. Simultaneous extraction of available zinc (Zn), copper (Cu), iron (Fe) and manganese (Mn) were carried out by using of 0.005 M diethyl triamine penta-acetic acid (DTPA), 0.1 M CaCl2 and 0.1M tri-ethanolamine adjusted to pH 7.3. The concentration of Zn, Cu, Fe and Mn in DTPA extract of soils was determined using Atomic Absorption Spectrophotometer (Model: ECIL 4141).
More than 90% of the soils of TGA are deficient in nitrogen (N) and phosphorous (P) and more than 60 per cent of the soils were deficient in available potassium (K). More than 95 per cent of the soils in the total geographical area are deficient in available iron (<4.5 mg kg-1) and zinc (< 0.6 mg kg-1). Soil available Cu and Mn are found above the critical limit of 0.2 mg kg 1 and 1.0 mg kg-1 respectively.
The Zn and Fe deficiency was consistent with vertical distribution also in soil pedons. The zinc got precipitated/fixed in the crystal structure of soil clays under alkaline conditions (pH >7). An increase in soil pH resulted in the formation of insoluble zinc hydroxide. Since these coarse textured soils were highly calcareous containing mainly of calcium carbonates which has increased the adsorptive capacity of the soils because of the ionic compatibility with Zn ion. Fe solubility decreases significantly in aerated soils especially at soil pH of 7-8, where most of the Fe is present as low soluble Fe3+ oxides and hydroxides. Soil pH is the most important soil parameter influencing Fe solubility and its availability to plants. Solubility of Fe decreases a thousand fold for each unit increase in soil pH in the range 4 to 9, and consequently, most Fe deficiencies occur on calcareous soils.
Impact of Extreme Weather Events on Khadin:
Negative implications of extreme weather events like droughts and floods are extremely high in arid regions, as the alternate sources of income is almost nonexistent. The drought results in insufficient water availability inside khadins during rainy season, which in turn reduce the productivity of grasses and crops.
This result in increased in food prices, reduced fodder availability for livestock, and thus ultimately led to reduced assets and food insecurity. Similarly to droughts, floods also result in loss of human life, livestock and crop damages, thus, ultimately lead to reduced assets and food insecurity.
Therefore, it is important to store enough food and fodder as a contingency measures in case of such extreme weather events in the areas where khadin system is prevailing. Also, it is essential to find some alternate source of income for the livelihood securities.
Following are the important strategies to manage the extreme weather events in arid regions i.e:
(i) Improving collection and dissemination of weather related information,
(ii) Establishing a regional early warning system of climatic risks/disasters,
(iii) Promoting insurance for climatic risk management,
(iv) Strengthening pest surveillance and forecasting mechanisms,
(v) Facilitating establishment of community partnership in food, forage and seed banks, and
(vi) Educating local farmers to be mentally strong and strategically sound to tackle and adapt to extreme weather events and climate change. Also detailed studies assessing impact of the extreme weather events on khadin system are needed to be undertaken in future.
Scope of Sustainable Agriculture in Khadins:
Khadins are cultivated to grow kharif and rabi season crops depending on amount of water stored in the lower reaches and water levels in tanks and wells. Generally, sowing is first carried out in the upper reaches followed by the lower reaches as the stored water recedes. Wherever groundwater level is good, farmers go for dug wells and bore wells with the financial aid of government agencies.
They also construct huge tanks through participatory approach and use the stored water through sprinkler irrigation for rabi crops. Application of gypsum is advocated for the reclamation of sodic soils. The use of zinc chelates is an effective way of providing zinc to plants under high soil-fixing conditions. Foliar application of NPK is effective in correcting NPK deficiency. Soil application of bio- phosphorous, zinc sulphate and foliar application of thiourea are helpful to improve the crop productivity.
Whenever the monsoon is below normal, water accumulation in the lower reaches of the khadins is poor, which is used to grow crops like pearl millet (Pennisetum typhoides L.) and clusterbean (Cyamopsis tetragonoloba Taub.) during kharif season. If monsoon is good, stored water can also be used for the cultivation of rabi crops like wheat (Triticum aestivum L.), mustard (Brassica juncea Coss.) and chickpea (Cicer aerietinum L.) either as sole or as mixed crop using conserved soil moisture.
The field experiments on pearl millet crops in years 2013 and 2015 in the khadin near Baoroli-Bambore in Jodhpur district have shown significant improvement in grain and straw yield over control. Soil application of ZnSO4 was beneficial to get 38.54 and 19.28% higher grain and straw yield respectively over control in the year 2013 and 22.59 & 23.85% higher grain and straw yield respectively over control in the year 2015.
The grain and straw yield respectively increased to the tune of 20.19 and 12.15% in the year 2013 and 20.68 & 20% in 2015 in response to foliar application of 1% NPK over water sprayed control. The agronomic experiments in Baoroli-Bambore watershed showed that pearl millet (MH 169) responded well to soil application of zinc [email protected] ha -1 as basal and foliar application of 1% NPK at flowering/ panicle initiation and improved the grain yield. The water use efficiency increased by more than 20 per cent with the application of zinc sulphate, thiourea and foliar application of 1% NPK.
In addition to cultivating agricultural crops, perennial woody trees like Azardirachta indica, Acacia nilotica and Prosopis’cinararia (L.) Druce can be grown which provide green leaf fodder for the cattle and it also improved soil quality due to their nitrogen fixing nature (Prasad et al., 2004). Fruit bearing trees such as Cordia myxa Linn., Cordia dichotoma, Zizyphus mauritiana Lamk and Phoenix dactylifera Linn., can be planted along the bunds of khadins which provide farmers consistent income every year besides protecting soils from wind and water erosion.