Crop and system yields
Fertilizer application significantly influenced the yield of rice, groundnut and of the system (Table 2). The mean yield advantages in rice grain due to application of recommended quantity of N, NP, NK and NPK over control were to the tune of 35, 60, 58 and 82%, respectively. Similarly, the increases in pod yield of groundnut due to application of N, NP, NK and NPK were 21, 68, 48 and 84% over control, respectively. However, the highest grain yield of rice (5.06 t/ha) and pod yield of groundnut (2.44 t/ha) were obtained with balanced fertilisation of NPK to both the crops along with ZnSO
4 to rice and CaSO4 to groundnut, respectively. This treatment (NPK + ZnSO
4) produced 90, 41 19, 21, 4 and 11% higher yield over the control, N, NP, NK, NPK and FP, respectively in rice and the treatment NPK + CaSO
4 in groundnut increased the pod yield to the tune of 94, 59, 15, 30, 5 and 16% over control, N, NP, NK, NPK and FP, respectively.
The rice-groundnut system productivity was evaluated in terms of rice equivalent yield (REY). Application of recommended quantity of N, NP, NK and NPK to both rice and groundnut in sequence increased the system REY by 29, 64, 54 and 83% over control, respectively. However, the highest system REY (12.63 t/ha) was recorded by application of recommended quantity of NPK with ZnSO
4 to rice and CaSO
4 to groundnut and the increases were 89, 47, 15, 24, 4 and 14% over the control, N, NP, NK, NPK and FP, respectively. The better yield performance under balanced application of NPK may be attributed to existence of synergistic interaction among these macronutrients. Phosphorus is involved in essential metabolic processes of plants including respiration and photosynthesis, helps in better root development, nitrogen fixation along with efficient use of N by plants. Potassium increases root growth, improves translocation of nutrients and is involved in N metabolism. The combined application of N and P increased the sorghum yield up to 85bu/ac (1 bushel/ac = 62.77 kg/ha), while N alone recorded a yield of 66 bu/ac
(Schlegel and Bond 2020). Similarly, combined application of both P and K together enhanced the yield of cornto64 bu/ac as compared to 38-41 bu/ac with P alone
(Usherwood and Segars 2001).
Ravisankar et al. (2014),
Hiremath et al., (2016) and
Panwar et al., (2019) have also reported better yield performance under balanced NPK fertilization than application of N alone.
Four prediction equations have been developed for rice grain, straw; groundnut pod and haulm yield (Table 3). Adj. R
2 values indicate that the models are best fit to the equations.
Partial factor productivity (PFP)
Application of balanced fertilizer improved the partial factor productivity (PFP) of applied N compared to application of N alone or NP and NK in both the crops and of the system (Table 4). Combined application of NP increased the PFPn by 19, 34 and 27% in rice, groundnut and rice-groundnut system, respectively, compared to that under sole N application. Similarly, combined application of NK increased the PFPn by 19, 21 and 20% in rice, groundnut and rice-groundnut system, respectively, over that under sole N application. However, the maximum increment in PFPn to the tune of 36, 46 and 42% in rice, groundnut and rice-groundnut system, respectively, were observed under balanced fertilization of NPK over sole N application. Similar to N, the improvement for PFP of P when combined with NK over application with N alone were 14, 10 and 11% in rice, groundnut and rice-groundnut system, respectively and the improvement for PFP of K when combined with NP over application with N alone were 16, 21 and 19% in rice, groundnut and rice-groundnut system, respectively.
Agronomic efficiency of nutrients
Agronomic efficiency (AE) of applied nutrients can be increased in rice, groundnut and rice-groundnut system by combined application of recommended quantity of N, P and K rather than sole application N or NP and NK (Table 5). Combined application of NP increased the AE of N by 73, 169 and 122% in rice, groundnut and rice-groundnut system, respectively instead of N alone and the AEn further increased to 139, 233 and 186% in rice, groundnut and rice-groundnut system, respectively, by applying recommended quantity of N with P and K rather than N alone. Similar to N, the improvements for AE of P when combined with NK over application with N alone were 38, 24 and 29% in rice, groundnut and rice-groundnut system, respectively and the improvements for AE of K when combined with NP over application with N alone were 43, 61 and 53% in rice, groundnut and rice-groundnut system, respectively.
Ravisankar et al., (2014) and
Panwar et al., (2019) have also reported higher agronomic efficiency of applied nutrients in cereal based cropping systems under combined application over their lone application.
Uptake of nutrients
Application of balanced fertilizer along-with ZnSO4/ CaSO
4 i.e. NPK+ZnSO4 to rice and NPK+CaSO
4 to groundnut recorded higher uptake of N, P and K by rice-groundnut system (Table 6). The increases in N uptakes due to application of recommended NPK+ZnSO
4 to rice and NPK +CaSO
4 to groundnut were found to be 89, 44, 15, 22, 3 and 14% over control, N, NP, NK, NPK and farmers’ practice respectively, while the respective increases for P uptakes were 88, 47, 12, 21, 3 and 12% and K uptakes were 82, 45, 18, 14, 2 and 14%. The uptake of N when applied along-with P (213.7 kg/ha) and uptake of N when applied along-with K (201.6 kg/ha) were higher by 25 and 18% respectively, over that under application of N alone. Similarly, the respective increases for P uptakes were 31 and 22% and respective increases for K uptakes were 23 and 28%. However, both the treatments (N with P or N with K) recorded lower N, P and K uptake compared to balanced fertilisation with NPK.
Patra et al., (2019) also reported higher uptake of nutrients under balanced fertilization in cereal based cropping system.
Economics of rice-groundnut system
Balanced application of NPK+ZnSO4 to rice and NPK+CaSO
4 to succeeding groundnut fetched maximum system net return (₹92,690/ha) followed by application of recommended NPK to both the crops (₹89,950/ha) (Table 2). This treatment also increased the system net return by 480, 113, 25, 40, 3 and 22% over control, N, NP, NK, NPK and FP, respectively, while the increases in respective cost of cultivation were only 13, 12, 7, 9, 4 and 6%. The increases in net return under application of N with P or N with K over N alone were 71 and 52%, respectively. However, both the treatments (N with P or N with K) recorded lower marginal returns compared to balanced fertilisation with NPK.
Singh et al., (2017) also reported higher net return with balanced fertilization in cereal-based cropping system. The benefit: cost ratio was higher under recommended application of NPK.