Analysis of cropping intensity and irrigation intensity in North Twenty Four Parganas district, West Bengal, India

In North Twenty Four Parganas district, cropping intensity increased from 209.29% in 1996/97 to 228.06% in 2015/16. During this study period, the increase in cropping intensity was recorded as 8.97% due to the effective use of modern technological inputs in agriculture (Table 1). Partial correlation indicates that the temporal change in cropping intensity is positively associated with irrigation intensity, the area under HYVs of cereals to total cereals area, and the use of chemical fertilizers (Table 2). During the study period, of these three modern technological inputs, the relationship between cropping intensity and the use of chemical fertilizers is moderately positive and statistically significant. Cropping intensity of 21 Agricultural Blocks in North Twenty Four Parganas district for the years 1996/97 and 2015/16 has been presented in Table 4. In 1996/97, the highest cropping intensity was reported as 277.41% in Gaighata and the lowest as 110.37% in Hingalganj Agricultural Blocks. Whereas, in 2015/16, the highest cropping intensity of 271.26% and the lowest of 111.80% were recorded in Amdanga and Sandeshkhali-II Agricultural Blocks, respectively. Over a period of 20 years, out of 21 Agricultural Blocks in this district, a negative change in cropping intensity was observed in five Agricultural Blocks, namely Sandeshkhali-II, Habra-I, Sandeshkhali-I, Gaighata and Minakhan (Table 4). During the period from 1996/97 to 2015/16, the rate of maximum negative change in cropping intensity was observed as −23.60% in Sandeshkhali-II, followed by Habra-I (−11.34%) and Sandeshkhali-I (−5.61%) Agricultural Blocks. A decrease in cropping intensity was observed in these Agricultural Blocks in spite of an increase in the use of modern technological inputs, namely irrigation water, HYVs of cereals and chemical fertilizers in Sandeshkhali-I and Sandeshkhali-II Agricultural Blocks, and the use of HYVs of cereals and chemical fertilizers in Habra-I Agricultural Block (Table 4). This decrease in cropping intensity in these Agricultural Blocks resulted from the occurrence of floods and waterlogged conditions due to heavy rainfall during the monsoon season in 2015 (DMS, North Twenty Four Parganas District 2017).

During the entire study period, the rate of maximum positive change in cropping intensity was reported as 51.57% in Barasat-I, followed by Barasat-II (36.46%) and Barrackpur (33.63%) Agricultural Blocks. In Barasat-I Agricultural Block, this positive change in cropping intensity is the outcome of the combined effects of the increasing use of irrigation water and of HYVs of cereals and chemical fertilizers. The expansion of the area under irrigation, seeds of HYVs, and the application of chemical fertilizers support multiple cropping which ultimately enhances cropping intensity (Bezbaruah & Roy 2002). In the case of Barasat-II and Barrackpur Agricultural Blocks, in spite of a decrease in irrigation intensity, cropping intensity increased, resulting from the significant increase in the use of HYVs of cereals and chemical fertilizers (Table 4).

Based on the cropping intensity of the Agricultural Blocks, North Twenty Four Parganas district was divided into the following three cropping intensity zones for 1996/97 and 2015/16 (Fig. 2).

Figure 2

In both 1996/97 and 2015/16, three Agricultural Blocks, namely Hingalganj, Minakhan and Sandeshkhali-II, were categorized within the low cropping intensity zone, whereas, during this period Haroa and Hasnabad Agricultural Blocks shifted from the low to moderate zone of cropping intensity. All these five Agricultural Blocks are situated in the Coastal Saline Region, which is part of the Indian Sundarbans delta and prone to severe natural disasters, such as cyclones, erosion and inundation (DPD, GoWB 2010). Monocropped areas dominate in this delta region due to the high salinity in the soil and water and an uneconomic underground irrigation system (Guha 2000). During this study period, the cropping intensity increased in Haroa Agricultural Block, resulting from the increasing use of HYVs of cereals and chemical fertilizers, whereas in Hasnabad Agricultural Block the increase in irrigation intensity and use of HYVs of cereals and chemical fertilizers enhanced cropping intensity (Table 4).

During the study period, three Agricultural Blocks, namely Amdanga, Barasat-I and Bongaon, shifted from moderate to high cropping intensity zones. In Amdanga and Barasat-I Agricultural Blocks, although irrigation decreased slightly, the use of HYVs of cereals and chemical fertilizers increased during this period. The increase in the use of modern technological inputs may be attributed as the reason Bongaon Agricultural Block moved from a medium to a high cropping intensity zone. In this Agricultural Block, irrigation intensity increased by 44.13%, the use of chemical fertilizers by 95.96%, and HYVs of cereals by 3.36% during this period (Table 4). Baduria and Gaighata Agricultural Blocks maintained their high status of cropping intensity and the remaining 11 Agricultural Blocks retained their moderate status of cropping intensity during the study period. In 1996/97, the irrigation intensity, the area under HYVs of cereals and the use of chemical fertilizers in Baduria Agricultural Block were higher than the district average. Whereas, in Gaighata Agricultural Block, the area under HYVs of cereals and the use of chemical fertilizers were higher than the district average. In 2015/16, irrigation intensity was slightly lower than the district average in Baduria Agricultural Block; however, this Block maintained high cropping intensity due to an increase in the use of chemical fertilizers and HYVs of cereals.

From 1996/97 to 2015/16, the net cropped area in this district decreased by 1,868 hectares, whereas the gross cropped area increased by 37,418.5 hectares. The conversion of agricultural land for shrimp cultivation, brick kilns and the occurrences of natural calamities were responsible for this reduction of net cropped area (DPD, GoWB 2010). In addition, agricultural land was reduced due to the expansion of urban settlements and commercial activities in this district (Dhali, Chakraborty & Sahana 2019; Bera & Das Chatterjee 2019; Das & Angadi 2020, Dhar et al. 2019). However, with the significant use of modern technological inputs in agriculture, cropping intensity increased in this district from 1996/97 to 2015/16. During this period, the increase was reported as 0.65% in irrigation intensity, 12.96% in the area under HYVs of cereals, and 91.66% in the use of chemical fertilizers in the entire district (Table 1).

In North Twenty Four Parganas district, the main source of irrigation water is ground water, which contributes to 93.28% of the total gross irrigated area in the district (DLIC, PMKSY & DM, North Twenty Four Parganas 2016). Irrigation intensity in this district was reported as 61.55% in 1996/97 and 61.95% in 2015/16 (Table 1). In 1996/97, the highest irrigation intensity was observed as 88.77% in Habra-II and the lowest as 31.14% in Hingalganj Agricultural Blocks. The highest irrigation intensity was found to be 79.44% in Gaighata and the lowest to be 35.17% in Sandeshkhali-II Agricultural Blocks in 2015/16 (Table 4). This study has revealed that intra district variations in irrigation intensity are highly perceptible; however, the progress in irrigation development in the entire district is almost constant.

Based on irrigation intensity, North Twenty Four Parganas district has been divided into the following three irrigation intensity zones for the years 1996/97 and 2015/16 (Fig. 3).

Figure 3

During the study period, a negative change in irrigation intensity was reported in 12 Agricultural Blocks and a positive change in the remaining nine Agricultural Blocks in this district. From 1996/97 to 2015/16, the maximum rate of negative change in irrigation intensity was found to be −31.68% in Habra-II, followed by Swarupnagar (−30.09%) and Baduria (−25%) Agricultural Blocks. During this period, the maximum rate of positive change in irrigation intensity was observed as 97.63% in Rajarhat, followed by Bongaon (44.13%) and Gaighata (33.62%) Agricultural Blocks.

Agricultural Blocks in the Coastal Saline Region suffer mostly from a paucity of irrigation water. In this region, out of the total gross cropped area, only 41.84% in 1996/97 and 44.53% in 2015/16 were irrigated. More than 50% of agricultural lands were kept as fallow lands, after harvesting the rainfed paddy grown in monsoon season in this region (DLIC, PMKSY & DM, North Twenty Four Parganas 2016).

Two residual maps have been drawn to examine the relationship between cropping intensity and irrigation intensity in the study area for the years 1996/97 and 2015/16 (Fig. 4). The residual lines with ‘0’ value on the map indicate the perfect relationship between cropping intensity and irrigation intensity. The areas with positive residual values on the map mean that both the agro-ecological conditions and the use of modern technological inputs in agriculture, apart from irrigation water, are conducive to increasing cropping intensity. Areas with negative residual values denote that, in spite of the use of irrigation water, cropping intensity is not substantial, which may be attributed to the adverse agro-ecological conditions and the use of other farm inputs at a lower rate.

Figure 4

In 1996/97, residual lines with ‘0’ values passed through Bagdah, Basirhat-I, Basirhat-II, Deganga, Habra-II and Rajarhat, Barasat-I, Barasat-II and Barrackpur Agricultural Blocks in the district. Positive lines crossed through Rajarhat, Bagdah, Bongaon, Gaighata and the central part of Baduria Agricultural Blocks, and negative lines passed through the Agricultural Blocks lying in the Indian Sundarbans delta and the central part of Deganga Agricultural Block.

In 2015/16, the relationship between irrigation intensity and cropping intensity changed in the district. In this period, ‘0’ residual lines passed through Gaighata, Deganga, Habra-I, Basirhat-I, Basirhat-II, Haroa and Rajarhat Agricultural Blocks. Residual lines with positive values passed through Swarupnagar and Baduria Agricultural Blocks and the western part of the district. Residual lines with negative values crossed through the northern and southern parts of this district.

The hierarchical clustering using the Ward method, based on two cluster variables, namely irrigation intensity and cropping intensity, was performed to show the nature of homogeneity of the 21 Agricultural Blocks in North Twenty Four Parganas district for the years 1996/97 and 2015/16. Three clusters with cluster criteria, and their corresponding Agricultural Blocks in the study area, are presented in Table 5.

One-way ANOVA was conducted to determine the significant differences in the mean scores of cropping intensity and irrigation intensity across three clusters (i.e. cluster-1, 2 and 3) for the years 1996/97 and 2015/16, respectively.

From the Test of Homogeneity of Variances, it is evident that the Levene's tests are not significant at 0.05 alpha level for both of the dependent variables (i.e. p =0.104 for cropping intensity and p =0.244 for irrigation intensity) in 1996/97. The ANOVA results in 1996/97 (Table 6) confirmed that the null hypothesis (i.e. all three clusters means are equal) is rejected in both cases. Hence, there are significant differences between clusters means in every case (for cropping intensity and irrigation intensity, p =0.000, i.e. <0.05).

Post-hoc tests (Tukey HSD) were conducted to identify which group mean was significantly different from each of the others (Table 7). It was confirmed, from the results of Post-hoc tests on cropping intensity, that cluster-1 is significantly different from cluster-2. Likewise, in cropping intensity, cluster-2 is significantly different from cluster-3. In cropping intensity, there is no statistically significant difference between cluster-1 and cluster-3. The Eta squared (η²) is calculated as 0.6367, i.e. 63.67% variance is associated with cropping intensity.

In 1996/97, for irrigation intensity (Table 7), cluster-1 is significantly different from cluster-2. Cluster-1 is significantly different from cluster-3. Cluster-2 is significantly different from cluster-3. The Eta squared (η²) is calculated as 0.8586, i.e. 85.86% variance is associated with irrigation intensity in 1996/97.

From the Test of Homogeneity of Variances, it is evident that the Levene's tests are significant at 0.05 alpha level for both of the dependent variables (i.e. p =0.029 for cropping intensity and p=.005 for irrigation intensity) in 2015/16. Therefore, the assumption of homogeneity of variance was violated in both cases. Hence, Robust Tests of Equality of Means (Welch and Brown-Forsythe) were conducted (Table 8) and the adjusted F ratio in all cases were significant (i.e. p <0.001) and, therefore, the null hypothesis was rejected. The Welch and Brown-Forsythe tests results confirmed that there were significant mean differences between clusters for cropping intensity and irrigation intensity in 2015/16.

The Games-Howell test was conducted as the Post-hoc tests in 2015/16, as the equal variance was not assumed (Table 9). In 2015/16, the results of Post-hoc tests (Games-Howell) on cropping intensity show cluster-1 is significantly different from cluster-2. Cluster-1 is significantly different from cluster-3 in cropping intensity. In cropping intensity, cluster-2 is significantly different from cluster-3. The Eta squared (η²) is calculated as 0.9284, i.e. 92.84% variance is associated with cropping intensity in 2015/16.

In comparison, cluster-1 is significantly different from cluster-2 in irrigation intensity in 2015/16. Cluster-1 is significantly different from cluster-3 in irrigation intensity. Cluster-2 is significantly different from cluster-3 in irrigation intensity. The Eta squared (η²) is calculated as 0.6726, i.e. 67.26% variance is associated with irrigation intensity in 2015/16.