Validation of fertilizer prescription equation evolved for Chhattisgarh dhan-1919 in a Vertisol

Introduction

The Green Revolution played a key role in making India self-reliant in food production. However, it also led to the excessive and unbalanced application of chemical fertilizers, which has negatively impacted soil health. This issue is especially concerning in areas of intensive farming, where crops extract large amounts of nutrients from the soil, yet replenishment through fertilizers remains both inadequate and disproportionately focused on nitrogen as a result, the productivity of major crops has either stagnated or begun to decline. At current levels of agricultural output and fertilizer application, it is estimated that there is a nutrient deficit of around 10 million tones, the difference between the nutrients taken up by crops and those added through fertilizers, organic sources of nutrients such as compost, crop residues, and bio-fertilizers have the potential to fill this gap. However, only about one-third of these available organic resources are currently being utilized in farming. This underuse is accelerating the depletion of the soil's nutrient reserves. Consequently, soil fertility is deteriorating rapidly, posing a serious risk to both agricultural productivity and long-term sustainability. Multiple approaches have been developed to recommend fertilizer use based on chemical soil testing, with the goal of maximizing crop yield per unit of fertilizer applied. Among these, the Soil Test Crop Response (STCR) method has proven particularly effective tools for fertilizer recommendations. This approach helps in formulating fertilizer adjustment equations and developing calibration charts, which guide fertilizer recommendations based on soil test results to achieve targeted crop yields (Ramamoorthy et al., 1967; Singh and Biswas, 2000) [8,11] .

The Soil Test Crop Response (STCR) approach plays a crucial role in maintaining sustainable crop yields while reducing both fertilizer inputs and overall cultivation costs (Saxena et al., 2008; Chatterjee et al., 2010) [10,3] . Fertilizer decisions should consider the crop's nutrient demands, the natural nutrient supply from the soil, and the short-and long-term effects of applied nutrients. One major factor contributing to reduced agricultural productivity is the inconsistent use of fertilizers by farmers. This often stems from a lack of knowledge about soil fertility and crop nutrient needs, leading to both nutrient toxicity and deficiencies, as noted by Ray et al. (2000) [9] . To address this, the AICRP center under the STCR (Soil Test Crop Response) project developed fertilizer prescription equations tailored for various crops and agro-ecological zones across different states. By inputting soil test results and target yield values into these equations, precise fertilizer nutrient recommendations can be generated. These values can then be converted into actual fertilizer application amounts. Using such a targeted approach not only helps conserve fertilizer and improve farm profitability but also promotes better soil health. Srinivasan and Angayarkanni (2008) [13] observed that applying fertilizers based on STCR equations can lead to nutrient buildup in the soil, which enhances its fertility over time. Additionally, applying nutrients as per soil test results tends to produce higher crop response ratios and better benefit-cost outcomes. Our national food security mission, rice crop plays an important role and is a means of livelihood for Millions of rural households. Rice is grown in Chhattisgarh in an area of 37.88 lakh hectares with a Production of 74.86 lakh tones and productivity of 2.15 tones/ha in 2023-24.

Materials and Methods

Experimental site and soil characteristics

The experimental site is located at the research field of IGKV, Raipur. Which is located near Zora village at eastern part of the state of Chhattisgarh, central India. The site lies at 21.250 N latitude and 81.620 E longitudes with an average elevation of 298.15 meters from above mean sea level. The experimental site belongs to the soil order of Vertisol, which is also locally known as Kanhar. Vertisol is neutral to alkaline in soil reactions due to presence of lime concretion in lower horizon, clayey in texture and dark brown to black in color. The initial soil test values were as pH 7.55, EC 0.21 ds/m, organic carbon 0.55%, available nitrogen 170 kg/ha, available phosphorus 16.42 kg/ha and available potassium 372 kg/ha.

Treatments

Using six different combination of fertilizer application along with Control (N 0 P 0 K 0 ), RDF (N 120 P 60 K 40 ), STCR based dose for YT 55q/ha without FYM (N 127 P 18 K 36 ), STCR based dose for TY 55q/ha with 5-ton FYM (N 120 P 16 K 34 ), STCR based dose for TY 65q/ha without FYM (N 174 P 30 K 49 ), STCR based dose for TY 65q/ha with 5-ton FYM (N 168 P 28 K 48 ). The study carried out on soil test based fertilizer prescription in a Vertisol. Before conducting the trial, the field divide in to four equal long strips denoted as R 1 , R 2 , R 3 and R 4 . The experiment was laid out in RBD design. For validation of fertilizer prescription equation evolved for Chhattisgarh dhan -1919 in a Vertisol was here FN= 4.72Y-0.70SN-0.25ON FP= 1.22Y-2.72SP-0.20OP FK=1.37Y-0.09SK-0.06OK Where FN, FP and FK are fertilizer N, P 2 O 5 and K 2 O in kg/ha, respectively. SN, SP and SK are soil test values for available N, P and K in kg/ha, respectively. ON, OP and OK are organic nutrients of N, P and K in kg/ha, respectively. Y is targeted yield of rice q/ha. The fertilizer N, P 2 O 5 and K 2 O were calculated on basis of soil test for the targeted yield treatments by using these equations. The following doses of fertilizer N, P 2 O 5 and K 2 O were applied to achieving the yield targets of 55 and 65 q/ha based on the soil test values with FYM @ 5 t/ha (treatments T4 and T6) and chemical fertilizer alone (treatments T3 and T5). Effect of different fertilizer treatments on plant height was found to be significant and has been presented in Table 1 and Fig 1 . The variation in plant height of rice was influenced by the application of different fertilizer doses. The maximum plant height (99.50 cm) was observed under the treatment with STCR based dose for target yield 65 q/ha with 5 ton/ha FYM. Treatment STCR based dose for target yield 65 q/ha (97.00 cm) followed by RDF (96.00 cm) and STCR based dose for target yield 55 q/ha with 5 ton/ha FYM (95.50 cm) gave significantly higher plant height than control (80.5 cm) and these treatments were statistically at par with STCR based dose for target yield 55 q/ha (94.75 cm) and each other's. The control plot recorded minimum plant height(80.50cm). The variation in plant height of rice was influenced by the application of different fertilizer doses. This may be because fertilizers play a role in promoting rapid leaf, stem and other vegetative part's growth and development. Similar results reported by Parihar et al. (2015) [6] and Choudhary et al. (2022) [4] .

Numbers of total tillers/m 2 and effective tillers/m 2

The numbers of total tillers/m 2 and effective tillers/m 2 have been represented in Table 1 and Fig 1 . Maximum number of total tillers/m 2 were observed in STCR based dose for target yield 65 q/ha with 5 ton/ha FYM (466.34) followed by STCR based dose for target yield 65 q/ha (463.03) and RDF (458.91). These treatments are statistically at par with each other. STCR based dose for target yield 55 q/ha have more tillers/m 2 (441.72) than control (295.97) and also at par with STCR based dose for target yield 55 q/ha with 5 ton/ha FYM (453.75). The maximum numbers of effective tillers/m 2 were found in STCR based dose for target yield 65 q/ha with 5 ton/ha FYM (358.26) followed by STCR based dose for target yield 65 q/ha (356.40) and RDF (345.00). These treatments were at par with each other. Similarly STCR based dose for target yield 55 q/ha with 5 ton/ha FYM (334.50) followed by STCR based dose for target yield 55 q/ha (330.00) and RDF (345.00) were also found at par with each other's and these treatments were found more effective tillers/m 2 than control (212.10).The increase in number of total tillers and effective tillers by application of NPK fertilizers and FYM can be attributed to soil condition with more availability and nutrients uptake, water and growth promoting substances to promote more tillers. Similarly result reported by Uddin et al. (2013) [14] and Bhavya et al. (2021) [2] .

The highest panicle length was observed in STCR based dose for target yield 65 q/ha with 5 ton/ha FYM (23.48cm) followed by STCR based dose for target yield 65 q/ha (22.95cm). STCR based dose for target yield 55 q/ha with 5 ton/ha FYM (22.53cm), STCR based dose for target yield 65 q/ha and RDF (21.95cm) were found statistically at par with each other. The smallest panicle length was observed in control (18.95cm). The panicle length was increased with the level of nitrogen dose. Increasing panicle length might be because nitrogen and balance fertilization contributes in stimulating cell division in the reproductive stage of crop growth. Similar findings reported by Bhavya et al. (2021) [2] and Choudhary et al. (2022) [4] .

Filled and unfilled grains per panicle of rice.

The result of filled and unfilled grains per panicle have been represented in Table 1 andFig 1. The maximum filled grains were recorded in STCR based dose for target yield 65 q/ha with 5 ton/ha FYM (182.94) followed by STCR based dose for target yield 65 q/ha (180.45). STCR based dose for target yield 55 q/ha with 5 ton/ha FYM (166.95), RDF (163.58) and STCR based dose for target yield 55 q/ha (150.75) have more filled grains than control (123.53) and also have at par with each other. Unfilled grains showed non-significant difference due to various fertilizations and maximum unfilled grains recorded in STCR based dose for target yield 65 q/ha (13.75) followed by STCR based dose for target yield 65 q/ha with 5 ton/ha FYM (12.50), STCR based dose for target yield 55 q/ha (12.25) and control (12.00). The minimum unfilled grains were found in RDF (10.50) and STCR based dose for target yield 55 q/ha with 5 ton/ha FYM (10.50). This is due to adequate supply of photosynthates from the source to the sink (grain). Accumulation of photosynthates to sink depends on the availability of nutrients and genetic potentiality of the crops. The similar results were obtained by Uddin et al. (2013) [14] and Aparna et al. (2017) [1] .

Test weight of rice grains

The Effect of different fertilizer treatments on test weight of rice grains showed in Table 1 and Fig 1 . The highest test weight was recorded in STCR based dose for target yield 65 q/ha with 5 ton/ha FYM (18.49 gm) and RDF (18.46 gm). The lowest test weight was recorded in control (18.25 gm). STCR based dose for target yield 55 q/ha with 5 ton/ha FYM (18.36 gm) and STCR based dose for target yield 55 q/ha (18.31 gm) were found almost equal test weight. STCR based dose for target yield 65 q/ha (18.41 gm) was also found almost equal test weight with RDF. Fertilizer application had non-significant impact on test weight of grains because test weight of a variety is genetically inherent character.

Grain and Straw yield of rice

Table 1 and Fig 1 were represented that grain and straw yield have been affected by the application of different fertilizer treatments. The highest grain yield was recorded in STCR based dose for target yield 65 q/ha with 5 ton/ha FYM (66.32 q/ha), which was also statistically at par with STCR based dose for target yield 65 q/ha (64.00 q/ha). Treatments RDF (58.58 q/ha), STCR based dose for target yield 55 q/ha with 5 ton/ha FYM (57.79 q/ha) and STCR based dose for target yield 55 q/ha (55.77 q/ha) were found statistically at par with each other. The lowest grain yield was recorded in control (31.06 q/ha). The grain yield was found +10 % variation from targeted yield under the application of different treatments 55 q/ha and 65 q/ha alone and along with 5 ton ha 1 FYM. So, it's proved that the fertilizer prescription equation developed previously was valid for Chhattisgarh dhan-1919 in a Vertisol. Significantly highest straw yield was recorded in STCR based dose for target yield 65 q/ha with 5 ton/ha FYM (83.23 q/ha), which was also statistically at par with STCR based dose for target yield 65 q/ha (79.30 q/ha). STCR based dose for target yield 65 q/ha, RDF (75.21 q/ha), STCR based dose for target yield 55 q/ha with 5 ton/ha FYM (73.99 q/ha) and STCR based dose for target yield 55 q/ha (69.24 q/ha) were also found statistically at par with each other. The lowest straw yield was recorded in control (37.65 q/ha). Results showed that the yield of rice was increased by addition of FYM. Similar results were observed by Rai et al. (2016) [7] and Kumar et al. (2023) [5] .

Conclusion

The maximum plant height was recorded in the treatment with STCR based dose for target yield 65 q/ha with 5 ton/ha FYM (99.50cm), which was statistically at par with other treatments except STCR based dose for target yield 55 q/ha and control. Significantly lowest plant height was recorded in control (80.50cm). The maximum number of total (466.34) and effective (358.26) tillers were found in the treatment with STCR based dose for target yield 65 q/ha with 5 ton/ha FYM, which was statistically at par with other treatments except STCR based dose for target yield 55 q/ha and control. The minimum number of tillers was found in control. The highest panicle length observed in treatment with STCR based dose for target yield 65 q/ha with 5 ton/ha FYM (23.48 cm), which was found statistically at par with treatment with STCR based dose for target yield 65 q/ha (22.95 cm). Significantly lowest panicle length observed in control (18.95cm). The maximum filled grains were observed significantly highest in treatment with STCR based dose for target yield 65 q/ha with 5 ton/ha FYM (182.94) followed by treatment with STCR based dose for target yield 65 q/ha (180.45). Control (123.53) was found significantly minimum filled grains. The unfilled grains found non-significant in treatments. The test weight of grains showed non-significant difference due to various application of fertilizers. The highest test weight recorded in treatment with STCR based dose for target yield 65 q/ha with 5 ton/ha FYM (18.49 gm) and lowest in control plot (18.25 gm).Significantly highest grain yield observed in treatment with STCR based dose for target yield 65 q/ha with 5 ton/ha FYM (66.32q/ha), which was found statistically at par with treatment with STCR based dose for target yield 65 q/ha (64.00 q/ha). The lowest grain yield observed in control (31.06q/ha). The highest straw yield was observed in treatment with STCR based dose for target yield 65 q/ha with 5 ton/ha FYM (83.23q/ha) and significantly lowest straw yield was observed in control plot (37.65q/ha). The grain yield received under targeted yield treatments YT 55 q/ha and YT 65 q/ha were achieved with + 10% variations due to fertilizer application alone or along with 5 ton/ha FYM as per yield target, so, its proved that the previously developed fertilizer prescription equations were valid for rice crop.

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