**4. Irrigation scheduling**

Irrigation scheduling is the process of deciding the period and quantity of irrigation water during the crop growth under different irrigation methods [24]. Its main objective is to apply irrigation at the right period and in right amount. Irrigation amount is determined in terms of gross irrigation requirement and pumping time per application, while, irrigation time is based on depletion of soil moisture content of the crop root zone reached at critical point [25]. That is basically dependent on the consumptive use rate of crop and method of water application to the plant root zone [26]. The quantity of irrigation water for each treatment was calculated based on the soil moisture content before irrigation and root zone depth of the plant using the Eq. 1.4:

$$\mathbf{SMD} = (\theta\_{\text{FC}} - \theta\_{\text{l}}) \times \mathbf{D} \times \mathbf{Bd} \times \mathbf{MAD} \tag{4}$$

Where,

SMD = Soil moisture deficit (mm). θFC = Soil moisture content at field capacity (%). θ<sup>I</sup> = Soil water content before irrigation (%).

*Climatic Variation and Its Impacts on Yield and Water Requirement of Crops in Indian Central… DOI: http://dx.doi.org/10.5772/intechopen.94076*

D = Depth of root development (mm). Bd = Bulk density of the particular soil layer (g cm�<sup>3</sup> ). MAD = Management allowable Depletion (%).

#### **4.1 Management allowable depletion (MAD)**

Producing optimal yield requires that the soil water content be maintained between an upper limit at which leaching becomes excessive and a lower point at which crops are stressed [27]. As water is removed from the soil through ET, there is a point below which the plant experiences increasing water stress. This point is known as the management allowable depletion (*MAD*). The typical MAD values considered are 33% for shallow-rooted, high value crops; 50% for medium-rooted, moderate value crops and 67% for deep-rooted, low value crops [28]. Selection of MAD value for different crops with respect to soil type, initial field capacity (FC), permanent wilting point (PWP), and threshold soil moisture content (TSMC) must be determined. Threshold soil moisture content ascertains what fraction of soil is allowed to dry before the next irrigation event. Threshold soil moisture content can be determined in the following form:

$$
\Theta\_{\rm TSMC} = \Theta\_{\rm FC} \text{-MAD} \left( \Theta\_{\rm FC} \text{-} \Theta\_{\rm PWP} \right) \tag{5}
$$

Where,

**3.3 Irrigation efficiency**

**3.4 Irrigation water requirement**

IR = irrigation requirement (mm).

Pe = effective rainfall (mm).

**3.5 Effective rainfall (Pe)**

**4. Irrigation scheduling**

of the plant using the Eq. 1.4:

SMD = Soil moisture deficit (mm).

θFC = Soil moisture content at field capacity (%). θ<sup>I</sup> = Soil water content before irrigation (%).

Where,

**16**

Etc = total crop evapotranspiration (mm).

tive rainfall on a daily basis or monthly basis.

Ge = groundwater contribution from water table (mm).

Wb = water stored in the soil at the beginning of each period (mm).

It is only a part of the rainfall that can be effectively used by the crop, depending on its root zone depth and the soil storage capacity. Total rainfall amount is not considered as effective rainfall; some part of rainfall may be lost through surface runoff, deep percolation or evaporation. FAO CROPWAT ver. 8.0 model could be used rainfall data and employs the USDA S.C. method approach to estimate effec-

Irrigation scheduling is the process of deciding the period and quantity of irrigation water during the crop growth under different irrigation methods [24]. Its main objective is to apply irrigation at the right period and in right amount. Irrigation amount is determined in terms of gross irrigation requirement and pumping time per application, while, irrigation time is based on depletion of soil moisture content of the crop root zone reached at critical point [25]. That is basically dependent on the consumptive use rate of crop and method of water application to the plant root zone [26]. The quantity of irrigation water for each treatment was calculated based on the soil moisture content before irrigation and root zone depth

SMD ¼ ð Þ� θFC–θ<sup>I</sup> D � Bd � MAD (4)

respectively [22].

*Agrometeorology*

below:

Where,

Irrigation efficiency is defined as the ratio of amount of water beneficially used by plant as evapotranspiration to the amount of water applied to the plant area. The irrigation efficiencies under different methods *i.e.* 40%, 50%, 55%, 75%, and 90% are taken for border, check basin, furrow, sprinkler, and drip irrigation system,

The irrigation water requirement represents the difference between the crop water requirement and effective rainfall. Other factors or losses have minimal effect on irrigation water requirement and can be neglected [23] as shown in the equation

IR ¼ ETc–ð Þ Pe þ Ge þ Wb (3)

θTSMC: Soil moisture content at threshold level (%).

θFC: Soil moisture content at field capacity (%).

θPWP: Soil moisture content at permanent wilting point (%).

The determination of soil moisture content at threshold level is most important factor for irrigation scheduling on real time basis. This value varies with crop, soil, climate and crop growth stages. Whenever the soil moisture content at field capacity is depleted through ET, percolation losses, etc. to equal or below the θTSMC value, irrigation scheduling must be given otherwise crop yield and plant growth will be affect harmful way.

### **5. Estimation of water requirement of major crops using CROPWAT model**

CROPWAT is a decision support tool developed by the land and water development division of FAO. CROPWAT model is extensively tested, widely accepted for calculation of crop water requirements based on soil, climate and crop data. In addition, the program allows the development of irrigation schedules for different management and the calculation of scheme water supply for varying crop patterns. CROPWAT ver. 8.0 model used weather data and employs the modified penmanmonteith approach used to estimate reference evapotranspiration on a daily basis. The meteorological data was taken from Agromet Observatory, ICAR-VPKAS, Experimental farm Hawalbagh, Almora. The mean annual rainfall at experimental site was 1000.13 mm. The general soil properties of the experimental field were used in CROPWAT model. Based on the details of soil characteristics, total available water was taken 135 mm m�<sup>1</sup> depth of soil. Infiltration rate was measured using double ring infiltrometer and the basic rate was 6.8 mm hr.�<sup>1</sup> and the unsaturated hydraulic conductivity was 0.77 cm h�<sup>1</sup> . The estimation of irrigation water requirement (346–376 mm, 131–189 mm, 1.4 mm, 1.3 mm, 78.6 mm, 93.5 mm 104.1 mm, 176 mm, 96.9 mm, 16.2 mm, 18.3 mm, 15.5 mm, and 7.4 mm of Rice, Wheat, Maize, Soybean, Vegetable Pea, Rajma, Barley, Tomato, French Bean, chili, okra, mustard


#### **Table 2.**

*Estimation of irrigation water requirement of major crops grown on experimental site using CROPWAT model.*

and cowpea crop, respectively) and irrigation schedule plan of major crop was calculated using CROPWAT Model as presented in **Table 2**.

#### **5.1 Water budgeting equation**

This equation could be used to measure evaporation, seepage from pond and volume of water available in pond. The water budget method of determining long term available water present in pond can be used as a standard for comparing other methods. This method is not most accurate, but could be used satisfactory for practical purpose. The volume of water available in pond can be calculated using this equation in the following form:

and fertilizer. It is the biggest practical alternative, low-cost as well as associated ecological advantages, compatibility to reduce poverty, role of the social dimension/ expansion are the key to global climate change mitigation and adaptation [7, 9, 12]. Carbon storage in agroforestry remains in aboveground biomass (wood biomass), leaf group (foliage), shrub, vine, herb, dead biomass (dead wood, litter) and below ground biomass (roots), soil organic carbon etc. According to Nair et al. [29], the world's vegetation carbon sequestration ability by major agroforestry systems is

*Carbon sequestration potential in vegetation of world's major agroforestry systems.*

**Agroforestry/land use systems Age Average vegetation C (Mg ha**�**<sup>1</sup> y**�**<sup>1</sup>**

*Climatic Variation and Its Impacts on Yield and Water Requirement of Crops in Indian Central…*

1. Fodder bank, Segu, Mali,South Africa, Sahel 7.5 0.29 2. Live fense, Segu, Mali, South Africa, Sahel 8.0 0.59 3. Tree based intercropping, Canada 13.0 0.83 4. Park lands, Segu, Mali,South Africa, Sahel 35.0 1.09 5. Agrisilviculture, Chhatisgarh, Central India 5.0 1.26 6. Silvopasture, South Oreogaon, USA 11.0 1.11 7. Silvopastoralism, Kurukshetra, India 6.0 1.37 8. Silvopastoralism, Kerala, India 5.0 6.55 9. Cocoa agroforestry, Makoe, Cameroon 26.0 5.85 10. Cocoa agroforestry, Durialban, Costarica 10.0 11.08 11. Shaded coffee, South-West Congo 13.0 6.31 12. Agroforestry woodlots, Partorico 4.0 12.04 13. Agroforestry woodlots, Kerala, India 8.8 6.53 14. Home and farm garden 23.2 4.29 15. Indonesian homegarden, Sumatra 13.4 8.00 16. Mixed species stand, Puertorico 4.0 15.21

*DOI: http://dx.doi.org/10.5772/intechopen.94076*

**)**

In Himalayan region of India agroforestry is promising and distributed in large area in different forms. The area ranged from 4.95 in a watershed to 137 ha in of North-west Himalaya (**Table 4**). Carbon storage ranged from 3.31 to 31.71 t/ha in

**System Area (ha) Region Author** Cardamom agroforestry 27.59 North-East Himalaya [30] Agroforestry 4.95 North-West Himalayan Watershed [31] Willow based agroforestry 137 North-West Himalaya [20]

listed in **Table 3**.

**Table 4.**

**19**

*Source: [29].*

**Table 3.**

Indian Himalaya (**Table 5**).

**7. Status of agroforestry in Himalaya**

*Reported area under agroforestry systems of Himalaya.*

$$\sum\_{i=1}^{12} P\_p + \sum\_{i=1}^{12} R\_{cbt} - \left[ \sum\_{i=1}^{12} S\_p + \sum\_{i=1}^{12} E v\_p + a \sum\_{i=1}^{12} \sum\_{j=1}^{n=crop} \text{WR}\_{crop} \right] = \sum\_{i=1}^{12} W S\_p \tag{6}$$

Where,

Pp = precipitation in surface area of pond (m3 ), Rcbt = runoff from conservation bench terraces areas or plain surface (m<sup>3</sup> ). SP = seepage losses from Pond (m<sup>3</sup> ), Evp = evaporation losses from Pond (m<sup>3</sup> ). WRcrop = water requirement of crop (m<sup>3</sup> ). WSp = water storage in pond (m<sup>3</sup> ).

#### **6. Ways to increase carbon storage in tree based land use systems**

Carbon sequestration can be enhanced by adopting plantations or agroforestry. Loss of carbon storage can be prevented by reducing felling of forests, blocking or reducing emissions from agricultural activities and by reduced use of energy, oil

*Climatic Variation and Its Impacts on Yield and Water Requirement of Crops in Indian Central… DOI: http://dx.doi.org/10.5772/intechopen.94076*


#### **Table 3.**

and cowpea crop, respectively) and irrigation schedule plan of major crop was

*Estimation of irrigation water requirement of major crops grown on experimental site using CROPWAT model.*

**Effective rainfall (mm)**

Vegetable pea 209.8 131.7 78.6 Barley 250 147.9 104.1 Rajma 123.3 29.7 93.5 Tomato 262.4 84.3 176 French Bean 166.9 70.1 96.9 Chili 310.6 370.7 16.2 Rice 434–505.9 464–491 346–376 Wheat 269.2–375.1 163–194.6 131–189 Maize 247.9 395 1.4 Soybean 350.6 494.4 1.3 Okra 234.9 470.1 18.3 Mustard 155 145.5 15.5 Cowpea 171.9 280.2 7.4

This equation could be used to measure evaporation, seepage from pond and volume of water available in pond. The water budget method of determining long term available water present in pond can be used as a standard for comparing other methods. This method is not most accurate, but could be used satisfactory for practical purpose. The volume of water available in pond can be calculated using

*Evp* þ *α*

Rcbt = runoff from conservation bench terraces areas or plain surface (m<sup>3</sup>

),

).

**6. Ways to increase carbon storage in tree based land use systems**

" #

X 12

*<sup>n</sup>*X<sup>¼</sup>*crop j*¼1

),

*WRcrop*

<sup>¼</sup> <sup>X</sup> 12

*i*¼1

**Irrigation water requirement (mm)**

*WSp* (6)

).

*i*¼1

).

).

Carbon sequestration can be enhanced by adopting plantations or agroforestry. Loss of carbon storage can be prevented by reducing felling of forests, blocking or reducing emissions from agricultural activities and by reduced use of energy, oil

calculated using CROPWAT Model as presented in **Table 2**.

**5.1 Water budgeting equation**

**Crop name Crop water requirement**

*Agrometeorology*

**(mm)**

this equation in the following form:

*Rcbt* � <sup>X</sup> 12

SP = seepage losses from Pond (m<sup>3</sup>

WSp = water storage in pond (m<sup>3</sup>

Evp = evaporation losses from Pond (m<sup>3</sup>

WRcrop = water requirement of crop (m<sup>3</sup>

*i*¼1

Pp = precipitation in surface area of pond (m3

*Sp* <sup>þ</sup><sup>X</sup> 12

*i*¼1

X 12

**Table 2.**

*Pp* <sup>þ</sup><sup>X</sup> 12

*i*¼1

*i*¼1

**18**

Where,

*Carbon sequestration potential in vegetation of world's major agroforestry systems.*

and fertilizer. It is the biggest practical alternative, low-cost as well as associated ecological advantages, compatibility to reduce poverty, role of the social dimension/ expansion are the key to global climate change mitigation and adaptation [7, 9, 12]. Carbon storage in agroforestry remains in aboveground biomass (wood biomass), leaf group (foliage), shrub, vine, herb, dead biomass (dead wood, litter) and below ground biomass (roots), soil organic carbon etc. According to Nair et al. [29], the world's vegetation carbon sequestration ability by major agroforestry systems is listed in **Table 3**.
