Physiological causes of transplantation shock on rice growth inhibition and delayed heading

Transplanting is an important rice cultivation method; however, transplanting shock commonly affects grain yield, and the mechanisms underlying the inhibition of growth, development, and delayed heading caused by transplanting shock have not yet been clearly elucidated. Here, we investigated the effects of seedling age, temperature, and root damage during transplanting on growth, development, and time to heading, both under artificially controlled and natural day length. Additionally, we investigated the impact of seedling root growth space and the potential mitigating effects of residual seed nutrients on young transplanted seedlings. The delay in heading in transplanted versus directly seeded plants was affected more by growth inhibition during the seedling period than by root damage during transplanting. However, root damage had an effect on the inhibition of leaf and tiller development, and the ratio of leaves to tillers increased because tiller development was inhibited more by transplanting shock compared with leaf development. Based on these findings, we propose factors reflecting the delay in growth due to transplanting shock that should be included for more accurate rice phenology modeling and suggest advantageous seeding conditions and transplanting methods for improved rice cultivation and yield in response to climate change.

Evaluation of Different Designs of Isolated Cells to Raise Single Rice Seedlings for SRI Mechanized Transplanting

Numerous benefits of the system of rice intensification (SRI) have been documented since SRI was popularized 30 years ago. To date, more than 58 rice growing countries are practicing SRI, covering around 4 million ha of paddy fields and involving more than 10 million farmers. Many paddy farmers shy away from practicing SRI due to extreme labour endurance and number of labors required, especially during transplanting and frequent weeding. The manual transplanting technique to ensure proper root establishment of the seedlings, makes SRI less appealing to many paddy farmers. Furthermore, the transplanting shock is a problem arises from manual transplanting technique needs to be solved that resulted to damaged roots causing delays in crop establishment and reducing productivity. Mechanized transplanting of the young single seedlings into the paddy fields at a wider plantation area eliminates drudgery and enables better exposure to sunlight, water, air, and nutrients. This paper presents a solution to overcome the problem of transplanting shock and the back-breaking manual transplanting, which was achieved by containing the roots of each seedling in a grid of isolated cells. Several designs of the isolated cells to contain the root system were fabricated and tested. These include using aluminum square cells, polyvinyl chloride pipe circular cells, biodegradable grid cells, biodegradable conical capsules, and germinated seeds sowed in a grid without isolated cells. The typical grid cell size was 15 mm by 15 mm with a depth of each cell varied from 40 mm to 60 mm. The most promising design was one with single seedlings raised in bio-degradable capsules arranged close together to fit the conventional rice seedling tray of 300 mm by 600 mm and can accommodate 684 capsules per tray. Upon reaching 2-3 leaf stage, the seedlings with undisturbed roots are ready to be transplanted into the paddy fields using the currently available rice transplante rs.

Influence of anthropogenic activities on the initial establishment and growth rate of introduced Senna siamea in Zomba-Malosa Forest Reserve, Malawi

The study was conducted along the Nkanya-Lusewa rivers catchment as hot spot in Zomba-Malosa Forest Reserve in Domasi area in Malawi to determine the influence of anthropogenic activities on the growth of Senna siamea planted by the community using integrated indigenous-technocrat model. The study focused on 28 gardens along the rivers whose owners encroached the forest reserve and willed to participate in the study. In total we planted 101 S. siamea seedlings within a distance of 10 m on either side of the study rivers and we determined tree total height, canopy height, canopy base diameter and canopy base area in February, May, August, and November in 2014 using a ruler. We found that the average tree total height and canopy height slightly decreased from February to November from initial 34.7 cm to 31.1 cm and 16.8 cm to 12.1 cm respectively due to impact of transplanting shock and bushfires which led to loss of tree tops and some branches but those of canopy base diameter and canopy base area increased slightly following sprouting of burnt seedling stems. We further found that tree growth rates varied among the gardens due to transplanting shock, post-planting care differences, soil moisture variation, and incidence of bushfires.

SRI-TRAY: BREAKTHROUGH IN NURSERY MANAGEMENT FOR THE SYSTEM OF RICE INTENSIFICATION

The major challenges envisaged by SRI practitioners to nursery management are high labour requirement and transplanting shock due to traumatic condition at the nursery. This study was aimed at creating innovative techniques for increasing the quality and transplanting potentials of seedlings vis- ă –vis to savings on water, seeds, nursery space as well as reducing the transplanting shock. It involved the use of the developed SRI-Tray having 924 square growing cavities with sliding base to facilitate seedling transfer. The parameters used were water requirement (WR), growing media (GM), nursery perimeter (NP) and age of seedling (AS). These were compared with conventional nursery methods (dry-bed, wet-bed and tray) to evaluate the growth performances for 10 days on seedling height [SH], leaf length [LL], leaf number [LN] and root length [RL]. The SAS revealed that SRI-tray had the highest significant values for SH, LL and RL with the mean values of 157.2mm, 110.3 mm and 89 mm. when compared with conventional practices on tray (125mm, 92mm and 52mm), dry-bed (86mm, 64mm and 42mm). The seed rate, nursery area and seedling age to support one hectare of planting area were found as 5.34kg, 36m2 and 8-10 days on SRI-tray against 15-50kg, 250 – 500m2 and 15 – 30 days on conventional practices. The water management was found to be high on conventional tray (Flat tray) with a nursery area of 250m2, if supply at 4cm height for 20 days, and then total water use for conventional flat tray is 200m3. While a significant saving was observed on SRI-tray with only 18m3 with a nursery space of about 36m2 when supplied at 5cm for 10 days.

Effects of Root Pruning on Germinated Pecan Seedlings

Root systems of pecan trees are usually dominated by a single taproot with few lateral roots, which are commonly thought to inhibit successful transplanting. This study aimed to evaluate early growth and root/shoot development of pecan seedlings in response to taproot pruning. Taproots of ‘Shaoxing’ seedling pecan trees were mildly (1/3 of the total length of the radicle removed) and severely (2/3 of the total length of the radicle removed) pruned at different seedling development stages shortly after germination. At the end of the first growing season, top growth was measured and then trees were uprooted so that root system regrowth could be evaluated. The results showed that root pruning had no impact on increases in stem height or stem diameter. However, pruning the taproot could stimulate primary growth in taproot branches. Root weight and the number of taproot branches per tree increased with decreasing taproot length. This study indicated that severe root pruning when three to five leaves had emerged resulted in root systems with more taproot branches and the greatest root dry weight after one growth season, which may increase survival and reduce transplanting shock.

PREDICTING NURSERY GROWTH AND TRANSPLANTING SHOCK IN RICE

Seedling growth in the nursery and the magnitude of shock experienced by the seedlings after transplanting can affect subsequent growth and development of transplanted rice (Oryza sativa). These two processes have not been adequately represented by rice growth simulation models. In this study, seedling growth in the nursery was described with respect to endosperm mobilization, dry matter (DM) distribution and seed size. In addition, the transplanting shock process was represented describing the crop development and growth in relation to seedling age at transplanting. These relationships, as two sub-models, were incorporated into CERES-Rice, a rice growth model, and their performances compared with independent field data. The nursery growth sub-model was also evaluated with another model, RIBHAB. Results of the comparison showed that the nursery growth sub-model, either with CERES-Rice or RIBHAB, closely predicted observed seedling growth. On the other hand, CERES-Rice overestimated root and leaf DM and underestimated culm DM, while RIBHAB underestimated all the growth traits considered in the evaluation. Transplanting shock period predicted by the sub-model closely mimicked observation, whereas CERES-Rice highly overestimated it. It is concluded that the developed nursery growth and transplanting shock sub-models can be incorporated into CERES-Rice and other rice growth models for better simulation of those growth processes.