Ph. D

The project entitled “Nano zinc nutrition in rice based cropping systems in high phosphorus soils” was conducted at College of Agriculture, Vellayani, Thiruvananthapuram, Kerala, during 2020-2025. The objectives of the study were to evaluate the response of rice to nano zinc in high P soils, study the residual effect of nano zinc nutrition on growth and yield of succeeding crops, study the P - Zn interactions and to identify the promising crop sequence in terms of system productivity and profitability. The study comprised three parts which were carried out at Integrated Farming System Research Station (IFSRS), Karamana, Thiruvananthapuram, Kerala during 2022-23. The first and second parts of the experiment were laid out in randomized complete block design with three replications using variety Uma (Mo 16) in virippu and mundakan seasons. The treatments comprised T1- [Soil application (SA) of ZnSO4 at 20 kg ha-1 (applied only in virippu season)], T2- [Nutri priming (NP) with nano Zn at 0.05%], T3- [NP with nano Zn at 0.05% + Foliar spray (FS) with nano Zn at 0.05% at maximum tillering (MT) stage], T4- [NP with ZnSO4 at 0.5%], T5- [NP with ZnSO4 at 0.5% + FS with nano Zn at 0.05% at MT stage], T6-[FS with nano Zn at 0.05% at MT and panicle initiation (PI) stages], T7- [FS with ZnSO4 at 0.5% at MT and PI stages], T8- [Control (Recommended Dose of Nutrients (RDN) without application of P and Zn)]. The RDN were 90:45:45 (N:P2O5:K2O) kg ha-1 modified as 64:22:53 kg ha-1 on soil test basis. The growth and yield attributes of rice were significantly influenced by nano zinc nutrition. Taller plants with the highest number of tillers per m2, higher leaf area per hill, leaf area index and dry matter production were recorded in T3 and was on par with T6 during both the seasons. The yield attributes viz., higher numbers of productive tillers per hill, grains per panicle, grain weight per panicle and lower sterility percentage were observed in T3 and was on par with T6 during both the seasons. The pooled mean over the seasons revealed that the grain yield (5161 kg ha-1) and straw yield (6148 kg ha-1) of rice were higher in T3 and was on par with T6. The grain yield increased by 78 and 69 per cent in T3 and T6, respectively over control. The nutrient uptake by plants at panicle initiation and harvest were significantly affected by zinc nutrition. The higher uptake of N, P, K, Ca and Zn by the rice plants at panicle initiation and harvest were observed in T3 which was comparable to T2 and T6 at panicle initiation and comparable to T6 at harvest during both virippu and mundakan. The nutrient use efficiency of P and Zn in terms of agronomic efficiency was the highest in T3 and T6, respectively during virippu and mundakan. The available nutrient status of the soil after each season was significantly influenced by nano zinc nutrition. The available N, P, K and Zn were higher in T3 and T6 during both virippu and mundakan. The dehydrogenase and phosphatase activities were significantly higher in T3 and were on par with T6. The highest net returns (₹ 76622 ha-1 and ₹ 86368 ha-1) and B:C ratio (1.74 and 1.82) were recorded in T3 during virippu and mundakan, respectively. The third part of the experiment was conducted during summer season to study the residual effect of nano zinc nutrition on growth and yield of succeeding crops. The experiment was laid out in strip plot design and was replicated thrice wherein, each individual plots of previous crop were divided to three sub plots and crops viz., grain cowpea (Kanakamony (PTB 1)) and bhindi (Anjitha) were grown in two sub plots and one sub plot was kept as fallow. The main plot treatments were residual nutrients of the previous seasons (N1 to N8) and the sub plot treatments were three crop sequences (C1- rice-rice-grain cowpea, C2- rice-rice-bhindi, C3- rice-rice-fallow). Growth, yield attributes and yield of summer crops viz., grain cowpea and bhindi were higher in N1. Available N, P, K, Zn, and soil enzyme activities were influenced by the residual nutrient status of the soil and crop sequences. Higher available N was observed in N6 and N5, available P, K and dehydrogenase activity were higher in N3, available Zn was the highest in N6, and phosphatase activity was higher in N1. Among the crop sequences, available P, Zn and dehydrogenase activity were the highest in C1. Among the interactions, the highest available Ca, available Zn and phosphatase activity were observed in n8c2, n3c1 and n1c1, respectively. The highest system yield (11504 kg ha-1) and system productivity (32 kg ha-1 day-1) were observed in N3 which was on par with N6. The crop sequence C2 recorded the highest system yield (10592 kg ha-1), while both C2 and C1 sequences showed higher system productivity. Among the interactions, n3c1 and n3c2 recorded the highest system yield (12100 and 12090 kg ha-1, respectively) and system productivity (33 kg ha-1 day-1, respectively). The highest energy efficiency, the lowest specific energy, the highest energy productivity and the highest energy intensity were recorded in N3. Among the crop sequences, C1 recorded the highest energy efficiency (7.42) and energy productivity was higher in C2 (0.62 kg MJ-1). Among the interactions, n3c3 recorded the highest energy efficiency. The data on nutrient balance showed a net gain of nitrogen in all treatments in C1 and C2, except N8. The rice-rice-fallow sequence showed a net gain in N3, and N6. Available phosphorus showed a net loss among all sequences and all treatments except N8. Potassium had a positive balance in the rice-rice-grain cowpea and rice-rice-bhindi in all treatments except N8. In rice-rice-fallow sequence, net gain of K was observed in N3 and N6. Zinc balance was positive in all the crop sequences and all the treatments except N1 and N7 which recorded net loss of Zn. Among the residual nutrients, the highest system net returns (₹ 173627 ha-1) and B:C ratio (1.49) were observed in N3 whereas, among crop sequences, rice-rice-bhindi (C2) showed the highest net returns (₹ 114127 ha-1) and B:C ratio (1.47). Among the treatment combinations, n3c2 recorded the highest net returns (₹ 182091 ha-1) and the highest B:C ratio (1.79) in n3c3. From the study, it can be concluded that nutri priming with nano zinc at 0.05% (50 ml ha-1) followed by foliar spray of nano zinc at 0.05% (250 ml ha-1) at maximum tillering stage along with soil test basis recommended dose of nutrients was effective way in enhancing the productivity and profitability of rice in high phosphorus soils. The growth and yield of grain cowpea and bhindi were the highest in residual nutrient with soil application of ZnSO4 at 20 kg ha-1 [applied only in virippu]. Rice-rice-bhindi was identified as the promising crop sequence in terms of system productivity and system profitability.