MSc

Sweet potato is an important food crop with short duration and high nutrient requirement. As the deficiency of secondary nutrients is generally encountered in highly leached acid soils of Kerala and the research on supplementation of these nutrients in enhancing the productivity of sweet potato is limited, the present study entitled “Response of sweet potato [Ipomoea batatas (L.) Lam.] to secondary nutrients” was carried out. The objective was to assess the influence of secondary nutrients on growth, yield and quality of sweetpotato.
The experiment was conducted from September 2019 to January 2020 at Agronomy Farm, College of Horticulture, Vellanikkara, Thrissur. The experiment was laid out in RBD with 11 treatments replicated thrice. The treatments included five levels of magnesium sulphate i.e., 0, 40, 60, 80 and 100 kg/ha along with N: P2O5 : K2O @ 75:50:75 kg/ha (KAU POP) and N : P2O5 : K2O @ 65:12:20 (soil test based). A high yielding sweet potato variety ‘Sree Kanaka’ was used.
Growth parameters like vine length, leaf area, and total dry matter accumulation per plant were significantly influenced by nutrient management. Higher doses of N: P2O5 : K2O (75:50:75) irrespective of MgSO4 dose (0 to 100 kg/ha) showed higher values for these parameters compared to treatments receiving lower doses of N : P2O5 : K2O (65:12:20) along with MgSO4. At 30 days after planting (DAP), vine length ranged from 40.5 cm to 55.6 cm and it increased to 2.5m by 90 DAP. At this stage, all the treatments exhibited comparable vine length irrespective of nutrient doses, except T3 (65:12:20 + MgSO4 @ 60 kg/ha) and T7 (75:50:75 + MgSO4 @ 40 kg/ha) which registered higher values and differed significantly from others. Higher and comparable total dry matter accumulation was also observed in treatments where N : P2O5 : K2O @ 75:50:75 along with varying doses of MgSO4 was applied.
The highest leaf area index of 3.48 was noticed in treatment T8 which received N : P2O5 : K2O (75:50:75) with MgSO4 @ 60 kg/ha and the lowest was seen in organic management (T11).
Chlorophyll content at 60 DAP was not significantly influenced by varied doses of nutrients applied.
Marketable tuber yield ranged from 19.8 to 35.9 t/ha and the treatments T7 (75:50:75 + MgSO4 @ 40 kg/ha) (35.9 t/ha) and T11 (organic management) (32.2 t/ha) resulted in higher tuber yields and were on par. Application of lower dose of N: P2O5: K2O based on soil test values resulted in lower yields compared to recommended dose. The highest harvest index of 0.72 was observed in T11 (Organic management) followed by T7 (0.60).
Unmarketable tuber yield ranged from 1.0 to 1.7 t/ha. Higher and comparable unmarketable yield was observed in treatments T2 (65:12:20 + MgSO4 @ 40 kg/ha) and T3 (65:12:20 + MgSO4 @ 60 kg/ha) which received lower doses of N : P2O5 : K2O and MgSO4 and registered lower marketable yield. The unmarketable yield was the lowest in superior treatment T7 (75:50:75 + MgSO4 @ 40 kg/ha).
Quality parameters of sweet potato tuber i.e. total, reducing and non-reducing sugar, crude fibre and crude protein were also estimated. In general, higher and comparable reducing sugar and total sugar content was observed in treatments which received higher doses of N : P2O5 : K2O and in tubers from organic nutrient management. Content of non-reducing sugar, crude fibre and crude protein did not vary significantly and the average values were 6.7, 2.6 and 14.3 % respectively.
The soil chemical parameters in post-harvest soil showed a decline in pH and EC except in organic management where an increase in soil pH could be observed. The organic carbon was influenced by nutrient management however, it was in medium range in all the treatments. The average N, P and K uptake by sweet potato was 281, 10 and 156 kg/ha respectively, and the corresponding values for calcium, magnesium and sulphur were 20, 13 and 17 kg/ha respectively.
Application of recommended dose of N : P2O5 : K2O along with 40 kg/ha magnesium sulphate resulted in the highest gross return (Rs. 5,38,500), net return (Rs. 4,05,619) as well as B:C ratio (4.1). Organic nutrient management system was the next best treatment with a net return of Rs. 2,88,050 and B:C ratio of 2.5.
Hence N : P2O5 : K2O @ 75:50:75 along with 40 kg/ha of magnesium sulphate can be recommended in soils deficient in Mg for enhancing productivity of sweet potato. The results also indicate that organic nutrient management also will be economically viable in sweet potato production if premium price can be assured for the produce.