Growth traits
Carrot plants grown in untreated acidic soil had lower plant height (PH) (30.10 cm), number of leaves plant
-1 (NLP) (8.33) and canopy spread plant
-1 (CSP) (38.81 cm), hence exhibiting significant inhibition of plant growth (Fig 1). The application of different organic amendments and potassium doses plus RF significantly improved the growth characteristics of carrot plants grown in strong acidic terrace soil Table 2. Treatment T
8 [RF + HC (5 t ha
-1)] showed the highest PHT (46.04 cm) and statistically similar data in T
3 (RF), T
4 (RF+ excess 25% K), T
5 (T
2 + PM (5 t ha
-1), T
6 (RF + PM (5 t ha
-1)], T
7 (T
2 + HC (5 t ha
-1), treatment (Table 2). Treatment T
6 [RF + PM (5 t ha
-1)], showed the maximum NLP (11.33) and responses were similar for all organic amendments and potassium treated plants (Table 2). Meanwhile, the T8 treatment showed canopy spread plant-1
i.
e. CSP (85.40 cm) (Table 2). Organic amended plants along with potassium doses showed more CSP i.e., in T
2 (49.87%), T
3 (81.36%), T
4 (105.34%), T
5 (86.67%), T
6 (114.12%), T
7 (105.54%) and T
8 (120.05%) than plots with untreated acidic soil (Table 2).
Yield and yield features
Yield-promoting parameters of acidic soil carrot plants were significantly influenced by the application of organic amendments and potassium doses plus soil test-based (SBTF) other fertilizers (Table 3). Plants in the control treatment had the lowest measurement for carrot root length (RL) (8.93 cm)
, root diameter (RD) (1.51 cm), stem fresh weight plant
-1 (SFWP) (18.90 g) and root fresh weight plant
-1 (RFWP) (41.35 g). The highest measurements for RL (16.58 cm), RD (3.64 cm) and RFWP (91.97 g) were observed in the T8 treatment. The maximum SFWP (37.23 g) was recorded in T4 treatment. Significantly increased by 56.16 - 85.63%, 78.19 -140.53%, 92.50 - 120.31%, 71.05 - 122.41%, RL, RD, SFWP and RFWP showed notable improvement when organic amendment and potassium rates were applied to plants grown in highly acidic soil (Table 3). The addition of organic amendments, in combination with potassium application, resulted in better yield traits.
Biomass yield of carrot plant
Different types of organic fertilizers and the addition of potassium plus rest RF had significant positive effects on the total fresh biomass plant
-1 (TBP) and the total fresh biomass yield (TFBY) of carrot cultivated in acidic terrace soil (Fig 1). Unmanaged acidic soil resulted in the lowest TBP (58.25 g) and TFBY (23.30 t ha
-1) in carrot plants. The organic amendments and potassium treated carrot plants displayed higher TBP and TFBY, contrast to abandoned acidic soil (control treatment). The T8-treated carrot plant produced the highest amounts of TBP and TFBY, with 129.20 g and 51.68 t ha
-1, respectively. Alike TBP and TFBY were produced in T
4 (123.17 g and 49.27 t ha
-1, respectively) and T
6 (122.26 g and 48.91 t ha
-1, respectively), treatment.
Economic productivity
The use of organic sources in combination with or without potassium and other chemical fertilizer exerted a notable and statistically significant (p<0.05) influence on carrot yield in strongly acidic terrace soil Table 4. The averaged data revealed that treatment T8 [RF + HC (5 t ha-1)] resulted in the highest marketable yield of carrot at 36.79 t ha
-1. These outcomes were found to be comparable with those obtained under T
4 (RF+ excess 25% K) and T
6 [RF + PM (5 t ha
-1)] treatment and remained significantly superior to the other treatments. Treatment T
2 (RF- K) exhibited a 31.33% rise in carrot production, which was statistically equivalent to that of untreated control treatment T
1.
Profitability
The T
8 plot, that received RF + HC (5 t ha
-1), had the highest total cultivation cost of 2477.08 US$ ha
-1 compare to other plots using various sources to apply OA +/- potassium (Table 4). On the flip side, the control plot had the lowest overall cultivation cost (2172.30 US$ ha
-1). The significantly (p<0.05) higher gross return (5025.92 US$ ha
-1) and net return (2548.85 US$ ha
-1) was registered under treatment, T
8 comparable with T
6 and T
4. The treatment T
8 listed the highest BCR (2.03) which was statistically at par with T
6 and T
4, but significantly better than all other treatments. The highest profitability (50.26 US$ ha
-1 day
-1) and production efficiency (350.35 kg ha
-1 day
-1) were significantly noted in T
8 comparable with T
6 and T
4.
Carrot yield and quality traits
The terrace soil is naturally acidic and impoverished, with low fertility and organic matter content, leading to disruptions in nutrient availability, buildup of acid-forming cations and consequently inhibiting crop growth and yield
(Binte et al., 2021; Khanam et al., 2022). The findings demonstrated that plant development, carrot yield and biomass productivity were significantly reduced in acid-prone terrace soil (Fig 1 and Table 2, 3). This might be due to soil acidification induced restriction of nutrient uptake and microbial activities such as organic materials mineralization, recycling of nutrients, nitrification and nitrogen fixation are inhibited or slowed down (
Gazey and Davies, 2009;
Binte et al., 2021). Moreover, the build-up of toxic cations like Al
3+ can hinder root growth by inhibiting cell growth and elongation, reducing cell division at the root tip, which in turn limits water and nutrient uptake, impacting plant growth and development
(Lauricella et al., 2020). The decrease in plant height, number of leaves and canopy area of carrot plants may be due to the soil acidity-induced macro-nutrients imbalance, which reduces the availability of nutrients to the roots and eventually disturbs the plant tissues. This would lead to a decrease in meristematic tissue activity and cell expansion. Although, chemical fertilizers contain higher amounts of nutrients and are in readily available forms, but cannot compensate for the decrease in biomass production brought on by low pH, due to the inherent terrace soil characteristics, losses and low uptake
(Nisar et al., 2020). The application of organic manure is important approaches for increasing of quantity and quality of plant products (
Arebu, 2022). A combination of organic and chemical fertilizers is more effective at increasing yield in acid soil than chemical fertilizer alone
(Wang et al., 2019).
Carrots require a lot of nutrients and can reach their maximum sustainable yield in poor soil with better nutrient management (
Ahmad, 2014;
Paramesh et al., 2023). Employing a diverse range of integrated organic and inorganic amendments decreased soil acidity effects and significantly boosted carrot plant growth (
e.
g. PHT, NLP and TFBY) and yield attributes (
e.
g. RL, RD, RFWP), showing effectiveness in alleviating soil acidity stress (Fig 1 and Table 2, 3). The significant higher amount of plant biomass and carrot yield was discovered in carrot plants treated with OA and potassium. The study demonstrates that among the amendment combinations, application of household compost with potassium gave the superior carrot yield in terrace soil (Table 4). Combining organic and inorganic amendments attributed to their positive impact on maintaining prolonged nutrient availability and uptake mechanism, positively impacting soil physical and biological properties, ultimately leading to increased biomass and yield of carrots (
Isaac and Verghese, 2016;
Nisar et al., 2019). The root size was directly impacted by the increased vegetative growth of the plants. This leads to more carbohydrates being stored, leading to an enlarged root diameter, which serves as a storage organ for food
(Bhandari et al., 2012; Annisha
Afrin et al., 2019). The collective use of OA (
i.
e. poultry manure and household compost) and potassium promoted auxin functions in plants, leading to higher RL, RD, RFW and consequently, the overall carrot production (Table 3 and 4). Utilizing organic amendments such as poultry manure and household compost improved the presence of essential nutrients like N, P, K and S, thus promoting nutrient sustainability in acidic degraded soil and enhancing crop productivity
(Hailu et al., 2024). Potassium, as one of the key essential nutrients, has tremendous potential for enhancing the growth of root crops
(Shikha et al., 2016). Potassium is a crucial plant nutrient essential for growth, metabolism and development. It activates over 80 enzymes involved in important plant processes like energy metabolism, starch synthesis and photosynthesis, promoting plant growth
(Shaban et al., 2018). The weight gain could be explained by the faster movement of photosynthates from the origin to the destination, affected by growth hormones triggered by the combination of OA and potassium, resulting in higher root production
(Nisar et al., 2019). The growth in root production could be a result of the combined impact of all components that contribute to yield, such as root diameter, root length and root fresh weight. Mineral composition of carrot root also enthused by addition of OA plus K to terrace soil signposted better nutrient balance in soil. Hence, utilizing a combination of both inorganic and organic sources (such as poultry manure and household compost) along with potassium application could be a suitable strategy for growing carrots in acidic terrace soil.
Profitability
The combined utilization of OA and RF, with or without K, had a notable impact (p<0.05) on the gross return, net return, B: C ratio, profitability and production efficiency of terrace-grown carrots. The absolute control plot had the lowest input cost and did not implement any management practices, resulting in the lowest production total, ultimately leading to the lowest net return, BCR, production and profitability efficiency for carrots. These patterns suggest that acidity is hindering the efficiency of carrot production in terrace soil. The treatment T
8, with RF + HC (5 t ha
-1), showed the highest improvement in the B: C ratio, profitability and production efficiency compared to the control, indicating a more effective carrot production in terrace soil (Table 7). Again, treatment T8 had the highest total production cost could be attributed to the greater expenses related to input costs, labor and other expenditures
(Avasthe et al., 2020). The data of the present study explained that organic amendments and fertilizers with potassium improves the soil’s physical, chemical and biological characteristics, resulting in higher carrot yields and economic productivity
(Babu et al., 2020; Singh and Kumar, 2024). Ultimately, the best economic outcomes, productivity efficiency and profitability in growing carrots was reached by combining potassium-enriched RF with OA. This implies that potassium and OA can offset the detrimental effects of soil acidity and could be a viable method for sustainable root crop production in terrace soil.