Effect of Nutrient Management Interventions on Nutrient Uptake of Rice-zero Till Ragi under Coastal Lands

Increasing awareness towards conservation of environment and also human health hazards associated with agrochemicals, consumer’s preference is to safe and hazard-free food are the major factors that lead to the growing interest towards organic agriculture in the world. Green revolution encourages greater use of off-farm agrochemicals viz., fertilizers and pesticides with adoption of new plant types and HYVs of crops have exponential increasing the production output per hectare in most cases. However, this increase in production has decline the soil fertility and productivity over a long run. The main principle of maintaining the soil fertility status is to annually replenish those nutrients which are removed by the crops from the field. For maintaining fertility status of soil on a longrun, we should dependent on the different nutrient sources rather than chemical fertilizers alone. Rice-pulse crop sequence is more predominant in north coastal zone and Krishna Godavari Zone of Andhra Pradesh. But, the area under this sequence (Rice-pulse) is recently declining due to late planting of rice because of delay in onset of monsoon and severe in cadence of yellow mosaic virus on pulse crop which lead to complete failure of pulse crop. In this context, ragi is an alternative crop in the rice fallows in place of pulse crops. The farmers of the North Coastal and Krishna zones are showing interest in raising of ragi as an alternative to pulse crop in the rabi season in rice fallows.

The present investigation was conducted at Agricultural College Farm, Bapatla on sandy loam during kharif and rabi seasons of 2017-18 and 2018-19 which is located at 15°54'N latitude and 80°25'E longitude with an altitude of 5.49 meters above the mean sea level (MSL) and about 8 km away from the Bay of Bengal coast. The soil was sandy loam in texture, slightly alkaline in reaction, low in organic carbon, available nitrogen and available phosphorus and medium in available potassium. The experiment was laidout in RBD with seven treatments, i.e., T₁ : 100% RDF (100-60-40 kg N-P-K ha^-1); T₂: 100% RDF + Soil application of ZnSO₄ @ 50 kg ha^-1; T₃: 125% RDF + Soil application of ZnSO₄ @ 50 kg ha^-1; T₄: 75% RDF + Poultry manure @ 0.82 t ha^-1 + Soil application of ZnS O₄ @ 50 kg ha^-1; T₅ : 75% RDF + FYM @ 5.0 t ha^-1 + Soil application of ZnSO₄ @ 50 kg ha^-1; T₆: 50% RDF + Poultry manure @ 1.6 t ha^-1 + Soil application of ZnSO4 @ 50 kg ha^-1 and T₇: 50% RDF + FYM @ 10 t ha^-1 + Soil application of ZnSO₄ @ 50 kg ha^-1. In rabi, each main treatment was divided into four sub plots and hence, in rabi the design was split plot design. The sub plot treatments are S₁: No fertilizer, S₂: 100% RDF, S₃: 75% RDF and S₄: 50% RDF. Nitrogen, phosphorus, potassium and zinc content and uptake of rice and in ragi calcium along with above four nutrients were estimated by following methods detailed below:
 
 
 
Nutrient uptake can be estimated by using this formula:

 
The data were statistically analyzed following the analysis of variance method as described by Panse and Sukhatme (1978).

Nitrogen content and uptake
 
In grain N content (Table 1) was higher in 50% RDF + FYM @ 10 t ha^-1 + ZnSO₄ @ 50 kg ha^-1 (1.60% and 1.63%) which was onpar with 125% RDF+ZnSO₄ @ 50 kg ha^-1 (1.53% and 1.57%) and T₆ (1.43% and 1.45%). Remaining treatments onpar with each other. In the straw also significantly the highest N content was recorded with T₇ (0.81% and 0.82%) but it was onpar with the T₃ (0.79% and 0.79%). Similar trend was followed in both the years of the study and in pooled data. Highest nitrogen uptake  (Table 3) in grain was recorded with the application of 50% RDF + FYM @10 t ha^-1 + ZnSO₄ @ 50 kg ha^-1 (85.5 and 88.9 kg ha^-1) and which was significantly superior with the rest of the treatments and in   starw, the highest nitrogen uptake was recorded with T₇ (49.7 and 53.4 kg ha^-1) and it was on par with the T₃ (45.2 and 47.5 kg ha^-1) but significantly superior over the rest of the treatments. Similar trend was noticed in both the years of study and in pooled data.

In no till rabi ragi, significantly the highest grain and starw nitrogen content in Table 5 (1.19, 1.29% and 0.37%, 0.35%) and uptake in Table 7 (22.12, 24.49 kg ha^-1 and 10.57, 10.82 kg ha^-1) was recorded with 50% RDF + FYM @ 10 t ha^-1 + ZnSO₄ @ 50 kg ha^-1 as residual effect and in fertilizer doses, 100% RDF (24.41, 26.34 and 8.04, 11.82 kg ha^-1) followed by S₃. Similar trend was followed in both the years of study and in pooled data.

The combined use of organic and inorganic fertilizers was found significantly better than inorganic fertilizers alone for N content and uptake. Integrated use of organic manures and inorganic fertilizers is helpful in maintaining higher concentration of soil NH₄+ N for a longer period and restore humus status of the soil ecosystem to hold its fertility and productivity, thus realizing higher N uptake of rice and ragi. These results are inconformity with the results of Kabat et al., (2006), Manuja et al., (2013) and Kumar et al., (2017).
 
Phosphorus content and uptake
 
In grain maximum P content (Table 1) observed with T7 (0.32%) which was significantly superior to the all treatments except T₃ (0.29%). In straw also similar trend followed as that observed in grain P content. Maximum recorded with T₇ (0.15%) and minimum was recorded with T₁ (0.07%). Similar trend was noticed in both the years of study and in pooled data.

The highest grain P uptake (Table 3) was recorded with application of 50% RDF + FYM @ 10 t ha^-1+ ZnSO₄ @ 50 kg ha^-1 (15.0 and 17.3 kg ha^-1) but it was onpar with 125% RDF along with 50 kg ZnSO₄ ha^-1. In straw, maximum P uptake (Table 3) was recorded with T7 (5.7 and 9.9 kg ha^-1) but it was remained onpar with T₃ (4.8 and 7.5 kg ha^-1). In the second year of study and pooled data also reported almost similar trend.

In rabi no till ragi, maximum phosphorus content in grain (Table 5 and Table 7) was recorded with T₇ (0.21% and 0.22%) which was onpar with the T₆ (0.20% and 0.21%) and T₅ (0.19% and 0.20%). However, it was found significantly superior to the rest of the treatments as a residual treatment. In straw, highest P content was noticed with T₇ (0.09% and 0.10%) which was followed by T₆ (0.07% and 0.08%) however, except T₁ remaining treatments were remained statistically onpar with each other. In the second year and in pooled data also followed similar trend.

Enhanced P content and uptake with judicious application of organic manures and inorganic fertilizers might be due to a combination of factors that enhance P availability in soils. These include production of organic acids through decomposition of organic matter and subsequent releases of phosphateions, formation of phospho-humic complexes  and isomorphic replacement of phosphateions by humate ions and also by synergistic effect existing between N and P due to application of organic manures. Similar findings are reported with Satheesh and Balasubramanian (2003). These results are in agreement with the findings of Kumar et al., (2017) and Kumar et al., (2018).
 
Potassium content and uptake
 
The highest potassium content in grain and straw (Table 2) was recorded with the application of 50% RDF + FYM @ 10 t ha^-1 + ZnSO₄ @ 50 kg ha^-1 (0.32 and 0.37%) but it was onpar with 125% RDF along with 50 kg ZnSO₄ ha^-1 (0.30 and 0.33%) in both the years of study in pooled data.
 
In grain, potassium content was did not differ significantly among the treatments. In straw, highest K content was noticed with T₇ (1.08% and 1.10%) which was followed by T₆ (1.00% and 1.01%) in rabi no till ragi as residual effect in both the years but in fertilizer doses, 100% RDF recorded significantly the highest potassium content (Table 6) over the rest of the treatments in both the years. Potassium uptake in grain and straw is concern (Table 8), T₇ as a residual treatment recorded significantly highest values as compare with remaining treatments. Among the fertilizer doses to ragi S₂ recorded significantly highest potassium uptake in both years and in pooled data.
 
Higher content and uptake of K might be due to the priming effect of organic manure on decomposition related release of organic acids that solubilise native K. In addition, higher magnitude of increases in K uptake by conjunctive use of organic manures and inorganic fertilizers showed that organic manures presumably play key role in enhancing the use efficiency of applied fertilizer as well as inherent nutrient availability in the soil. This was also documented earlier by Singh et al., (2001) and Singh and Singh (2018).
 
Zinc content and uptake
 
The maximum zinc content in grain (Table 2) was noticed with T₇ (30.33 and 32.33 ppm) which was on par with T₃ (27.33 and 28.33 ppm). In straw T₇ recorded the highest zinc content (25.67 and 27.00 ppm) which remained statistically on par with 125% RDF + FYM @ 10 t ha^-1+ ZnSO₄ @ 50 kg ha^-1 (22.33 and 23.17 ppm). Similar trend was noticed with second year and pooled data also.
 
In grain, significantly the highest zinc uptake (Table 4) was noticed with T₇ (162.4 and 177.1 g ha^-1) followed by T₃ (132.6 and 141.3 g ha^-1). Similar trend was noticed with zinc uptake in straw as noticed that in grain zinc uptake in both the years of study.

In no till rabi ragi T₇ as a residual treatment recorded maximum zinc content (Table 6) and uptake (Table 8) in grain and straw in both the years of study and in fertilizer doses S₂ recorded significantly superior over the rest of the treatments.
 
These results are inconformity with the findings of Kumar et al., (2014); Kandali et al., (2015); Singh et al., (2016); Alagappan and Venkitiswamy (2016); Sarkar et al., (2016); Naher and Paul (2017) and Kumar et al., (2018).