Growth parameters
The height of rice plants progressively increased with advancement in age and the tallest plants were observed at the time of harvest (Fig 1). The height of the plant was primarily influenced by the culm height until it reached the heading stage. Afterward, the length of the panicle played a crucial role in determining the overall height of the plant. The precision nutrient management treatments had a significant impact on plant height at all the stages of growth. Among the treatments, the SI-based N management treatment recorded significantly taller rice plants over absolute control (no fertilizer application) at 30, 60, 90 DAT and at harvest. Nitrogen is a crucial element found in chlorophyll and contributes to cell division and elongation. Phosphorus is involved in energy transfer, photosynthesis, and the movement of nutrients to various plant parts. Potassium also plays a vital role in the transportation of water, nutrients and carbohydrates within the plant, as well as in the activation of enzymes. These factors could explain the observed outcomes.
A perusal of data indicated a progressive increase in number of tillers per square meter up to 60 DAT and then declined thereafter towards maturity irrespective of precision nutrient management (Fig 2). Nevertheless, among the treatments, the SI-based N management noted significantly maximum number of tillers per hill compared to control. The growth of tiller primordium relies on the appropriate and sufficient supply of macro-nutrients, especially nitrogen. Nitrogen plays a crucial role in increasing the cytokinin levels within the tiller nodes and promoting the sprouting of tiller primordium. However, as the number of tillers increases over time, a competition arises for nutrients, light and moisture. The competition among tillers leads to a higher degree of variation in the distribution of photosynthates. To effectively address this issue, the natural occurrence of tiller mortality proves to be highly advantageous.
The earlier research conducted by
Subedi et al., (2019); Ali et al., (2015) and
Bhat et al., (2022) in rice supports the aforementioned discussion regarding plant height and the number of tillers per square meter observed at various dates.
Culm dry matter accumulation
The perusal of data presented in Table 1 revealed a significant influence of precision nutrient management on culm dry matter accumulation at all the three growth stages,
viz., tillering, heading and maturity stages analyzed in this study. Among all the treatments, SI-based N management with an index value less than 90 per cent was noted to record the significantly highest accumulation of dry matter into the culm during tillering and heading stages. The treatments namely nitrogen management based on LCC with a threshold of 4, nutrient management guided by NE and RCM at tillering stage performed equally well. At heading stage, the treatments like 125% RDF, LCC 4 based nitrogen management and the application of 100% RDF followed by nano urea spray at a rate of 2 ml/L during panicle initiation remained on par with the superior treatment. At maturity, 125% RDF recorded to be superior in terms of culm dry matter accumulation and remained on par with all the treatments under comparison except with absolute control which exhibited the lowest culm dry matter accumulation. Plant nutrients perform various important functions throughout different stages of crop growth. During the vegetative stage, nitrogen enhances plant vigor by stimulating the growth of tillers, increasing leaf size and number. Phosphorus, on the other hand, contributes to root development, while potassium strengthens the culm and provides resistance against both biotic and abiotic stresses. The quantity and timing of nutrient application are crucial factors that influence the accumulation of dry matter in the culm. As the crop progresses towards the heading stage, the culm dry matter gradually increases. However, after this stage, there are no significant differences in culm dry matter accumulation. Interestingly, treatments with a higher proportion of potassium compared to increased nitrogen application demonstrate an increase in culm dry matter production at maturity. In contrast, other treatments exhibit a declining trend, which can be attributed to specific physiological role of nutrients in rice. Previous findings of (
Amanullah and Inamullah, 2016;
Wu et al., 2023) in rice and
Santana et al., (2023) in sugarcane regarding culm dry matter were in corroboration with this discussion.
Leaf dry matter accumulation
The data revealed that the leaf dry matter accumulation was significantly influenced by precision nutrient management during tillering, heading and maturity stages (Table 2). At tillering stage, SI-based N management with an index value less than 90% was found to record the significantly highest leaf dry matter accumulation which remained on par with nutrient management guided by NE and RCM. Similarly, at heading stage, SI-based N management with an index value less than 90 per cent was found to record the significantly highest leaf dry matter accumulation and these results were comparable with leaf dry accumulated by 125% RDF, nitrogen management based on LCC with a threshold of 4, 100% RDF with and without additional application of nano urea spray at 2 ml/L during panicle initiation, nutrient recommendation using RCM and nutrient recommendation using NE. At maturity, the highest dry matter accumulation was observed with application of fertilizers at 125% RDF which was closely followed and remained on par by all the treatments under comparison except with application of fertilizers at 75% of the recommended dose and absolute control which recorded the lowest leaf dry matter accumulation. Leaves play a vital role in conducting photosynthesis, making them an important site for active metabolic activities. When evaluating the photosynthetic contribution of various plant parts during maturity, it is essential to consider the longevity of the green tissue. While the panicle tends to turn yellow relatively early during ripening, the leaves should retain their green colour for a longer duration. This longevity is primarily influenced by the availability of nutrients in accordance with the crop’s requirements. Of all the primary nutrients, nitrogen plays a particularly crucial role in determining the functionality of leaves from the heading stage until maturity. This is because nitrogen levels are closely associated with the chlorophyll content in rice crop. These findings corroborate with the findings of
Song et al., (2020) and
Yao et al., (2014).
Panicle dry matter accumulation
The data on panicle dry matter accumulation was recorded heading and at maturity (Table 3). During heading and maturity stages, the highest panicle dry matter accumulation was noted by SI-based nitrogen management with a threshold value less than 90% which remained on par with 125% RDF and LCC-based nitrogen management at a threshold 4 while the lowest panicle dry matter accumulation was noted by absolute control. After heading, nitrogen uptake becomes increasingly significant, especially when aiming for high yields by increasing the harvest index. The SI-based N management approach ensures the optimal supply of nitrogen during critical crop growth stages, leading to improved translocation of the absorbed dry matter from the straw to the primary sink. The higher allocation of dry matter to panicles at maturity indicates an enhanced movement of dry matter from leaves and culms towards the grain-bearing structures or sink during the grain filling period. These findings are supported by the earlier findings of
Meena et al., (2019) and
Paul et al., (2021).
Shoot dry matter accumulation
The data on shoot dry matter was recorded at tillering, heading and maturity stages and present in Table 4. The data reveals an increasing trend in shoot dry matter accumulation with the advancement in age of the rice crop and percentage accumulation of shoot dry matter was comparatively higher between tillering and heading than between heading and at maturity. At tillering stage, the significantly highest dry matter accumulation was recorded by SI-based N management at a threshold value less than 90% which remained on par with nutrient management guided by NE and RCM. At heading stage, SI-based N management at a threshold value less than 90% was found to be significantly superior to control in terms of shoot dry matter accumulation and remained on par with 125% RDF and LCC-based N management at a threshold 4. At maturity stage, the highest dry matter accumulation was observed with application of 125%RDF which remained on par with SI-based N management at a threshold value less than 90%, LCC based nitrogen management at a threshold 4, 100% RDF with additional application of nano urea at 2 ml/L during panicle initiation, 100% RDF without nano urea application and nutrient management guided by RCM. The absolute control treatment consistently displayed the lowest dry matter accumulation across all three phenophases under consideration.The reason behind this occurrence could be attributed to the fact that precise nutrient management enhances the availability of nutrients, leading to an increased conversion of carbohydrates into proteins. This heightened protein synthesis stimulates cellular activities in the growing regions of the plant, such as cell division and elongation. These physiological processes manifest in visible traits like taller plant height and a greater number of tillers per plant. Consequently, this contributes to a greater accumulation of dry matter in the above-ground parts of the plant. The findings in this trial were similar to the earlier findings of
Nayaka et al., (2021) and
Puteh et al., (2014).
Dry matter partitioning
During the early growth stage of rice, specifically the tillering phase, there were no notable differences in the percentage of dry matter partitioning between the leaves and culms when precision nutrient management was employed (Table 5). However, the partitioning of dry matter into the leaves was higher than that into the culms at the tillering stage. As the growth stages advanced towards heading and physiological maturity, there was an increase in shoot dry matter accumulation when nutrients were adequately supplemented through real-time demand monitoring. During the heading stage, a larger proportion of dry matter was allocated to the leaves compared to the culms and panicles. However, this trend changed at maturity, where the highest proportion of dry matter was allocated to the panicles. The shift in dry matter allocation towards the panicles at maturity can be attributed to the reproductive phase of the rice plant. The panicles, being the reproductive structures responsible for grain production, require a greater share of assimilates for seed development. This allocation strategy optimizes the plant’s resources to maximize grain yield during the crucial reproductive phase. Similar findings were observed by
Mahajan et al., (2012) and
Paul et al., (2021).
Among the treatments at maturity, The SI-based N management at a threshold less than 90% was observed to be the most efficient precision nutrient management strategy which allocated around 53.46% of the total shoot dry matter to the panicle. Conversely, the poor accumulation as well as translocation of assimilates occurred in absolute control. This indicates the role of primary nutrients in accumulation and translocation of accumulated biomass. The SI-based N management facilitated a greater translocation of assimilates towards the reproductive structures of the plant, promoting panicle development and ultimately leading to increased grain production might be due to availability of nitrogen at peak period of crop demand. Similar observations were found earlier by
Moe et al., (2019) and
Stuerz and Asch (2019).
Yield and yield attributes
The yield attributes such as effective tillers per square meter, number of spikelets per panicle and number of filled spikelets panicle were significantly influenced by precision nutrient management (Fig 3) and SI-based N management expressed a significant superiority in production of all these yield attributes which might be due to adequate availability of nitrogen at peak period of demand.
The precision nutrient management had a notable effect on the production of rice grain and straw (Fig 4). The SI-based N management resulted in significantly higher grain yield compared to the absolute control. The adoption of SI-based nitrogen management yielded a substantial 16.68% improvement in rice grain and a 13.17% increase in the overall yield of rice compared to the conventional approach of applying 100% RDF at fixed time intervals. The main reason for these outcomes could be attributed to the sustained greenness of leaf during the ripening stage which increased production and allocation of photosynthates from the source to the grain. Similar findings were reported by
Santos et al., (2019) and
Singh and Khind (2015).
In terms of straw yield, application of 125% RDF showcased better results compared to other treatments, but it was on par with SI-based nitrogen management. Applying 125% RDF resulted in a significant 10.68% rise in straw yield compared to 100% RDF and an impressive 65.11% increase when compared to the absolute control. However, the straw yield achieved from 125% RDF was similar to that obtained from 100% RDF. The enhanced response observed with the application of 125% RDF can be attributed to the additional supply of potassium compared to the recommended dose. This conversation aligns with the previous research conducted by
Islam et al., (2016) and
Akter et al., (2023). However, the positive impact of the excess potassium was counterbalanced by the timely and appropriate application of nitrogen through SI-based nitrogen management, along with the recommended doses of phosphorus and potassium.