Sugarcane growth variation based on rainfall and soil permeability in Takalar, Indonesia

The germination and sprouting phases of sugar cane are critical periods that determine productivity. This phase occurs when the sugar cane is 1-3 months old and requires an adequate supply of water to support the formation of shoots. Poor soil conditions and high rainfall can cause the failure of bud formation. This study aims to determine the relationship between rainfall and soil permeability in successfully constructing sugarcane shoots. We divided the 1 ha research area into nine points (A, B, C, D, E, F, G, H, I) to observe plant growth and soil permeability. The growth factors measured included the number of stems, diameter, and plant height, measured by zigzag. Intact soil samples at a 0-15 cm depth were then analyzed in the laboratory using Darcy’s law to determine the value of soil permeability. The results showed variations in sugarcane growth in the nine study plots. The average number of sugarcane stalks is eight stalks/meter with a height of 159 cm and a diameter of 3 cm. The low soil permeability value of 0.13-0.5 cm/hour cannot compensate for the average rainfall during the budding phase, thereby suppressing plant growth by up to 50% of the average productivity that should be.


Introduction
Sugar cane productivity in a field is primarily determined by the number of tillers that grow.The budding phase is critical and requires extra attention.Sufficient water supply dramatically affects the average yield of sugarcane production, significantly impacting sugar levels at harvest [1].Drought problems due to lack of water and inundation due to excess water are the main obstacles to achieving high production [2].Water scarcity during the dry season results in water stress and changes in rainfall distribution, so the air temperature increases [3,4].It was changing weather phenomena, including rain intensity which sometimes decreases or sometimes increases, resulting in the difficulty for plants to adapt during the growth process [5].
In addition to adequate water supply, soil physical properties play an important role in crop yields because it is a medium for channeling water and nutrients for plants [6].The use of agricultural mechanization in cultivating the soil usually harms the soil, namely compaction or narrowing of the soil pores so that the soil cannot store enough water [7].The main cause of the decrease in the physical properties of the soil caused by land processing using mechanized tools comes from the force generated by the tractor wheels [8].Most of the biodiversity is also located in the soil, and these biotas have a major influence on plant growth and even soil-borne pests [9].However, soil's most important role is supplying water and providing plant nutrients.In the soil's physical properties, the ability of the soil to pass and store water can be seen from its permeability value.
Soil pores have surface attraction and capillarity to draw water into them.Then, water fills the micro pores in the soil and allows water movement.Plant roots absorb water stored in soil pores [5].If the soil experiences compaction, it means that the number of soil pores is small and results in the soil not being able to store water or pass water properly so that during the dry season, there is drought, and during the rainy season, there is inundation [10].This main problem causes sugar cane seedlings to rot and not grow optimally.In this study, we examine the causes of the low tillering of sugarcane and relate it to soil conditions and the intensity of existing rainfall.Then, with the discovery of the main problems of decreasing sugarcane productivity in Takalar, further research can be carried out to overcome these problems.

Study area
This research was conducted on a sugarcane plantation in Takalar, Indonesia.The land used is 1 ha without any treatment to determine the conditions for sugarcane growth following the actual situation in Takalar.We divided the 1 ha area into nine sections ( A, B, C, D, E, F, G, H, I) with a size of 30 x 30 m to observe variations in sugarcane growth in the same area.Soil processing and sugar cane maintenance are carried out following the Standard Operating Procedure (SOP) of the Takalar Sugar Factory.

Collecting Data
Intact soil samples in the field were collected when the sugarcane was three months old, so the plants were not damaged by digging the soil.Then, measurements are carried out every two months to measure plant productivity, especially the number of stem, stem height, and stem diameter.Plant productivity measurements were carried out zig-zag along 7.5 m in each plot.Then the measurement results obtained will be averaged.Rainfall data and the average temperature in the Takalar area were obtained from the rainfall station belonging to the Takalar Sugar Factory For soil permeability measurement based on Darcy's law.

𝐾 = 𝑄. 𝐿 𝐴. 𝑡. ℎ
Where: K: Hydraulic Conductivity (cm/hour) Q: Amount of water flowing per measurement (ml) L: Thickness of soil sample (cm) A: cross-sectional area of the soil sample (cm 2 ) t: Measurement time (hours) h: height of the water surface from the ground (cm)

Results and discussion
Sugarcane in the study area was planted in November 2020 and harvested in October 2021.The sugarcane germination phase took place when the sugarcane was 1-3 months old, so in this study, the germination period occurred from December to February (Figure 2).The moderate rainfall category includes the rainfall value during the sugarcane germination phase (20-50 mm).Rainfall increases significantly in December, with 20 rainy days.The highest monthly average rainfall in one planting period was 23.57mm in December.In January, the average monthly rainfall decreased slightly to 23.16 mm.However, the maximum number of rainy days in January is 28 days which shows that it rains almost every day, so the sunshine duration is low [11].The highest air temperature in one planting period in Figure 3   Even though the intensity of rainfall in December and January is moderate, the facts on the ground show the occurrence of inundation on the land.The low ability of the soil to pass water can be seen from the value of soil permeability or the velocity of movement of a liquid in a porous media in a saturated state [12].In soil tillage using mechanization tools, the pore space under the tillage layer will narrow due to the pressure from the tractor wheels.Then, high rainfall intensity worsens soil conditions.There are significant differences in Figure 3 between plots A, B, C, D and E, F, G, H, and I.The permeability values in the A-D plots did not significantly differ before and after processing.Plot E-I before tillage has a higher soil permeability value than after tillage.The real difference can be seen in plot H which has a fast permeability value before tillage, then decreases after tillage becomes very slow.Soil permeability was measured at a depth of >20 cm at nine experimental points in one hectare of the soil before and after tillage when the sugarcane was three months old.The research results show variations in permeability values at the nine sampling points.With tillage, there is a decrease in the permeability value (Figure 2).This value indicates that using agricultural mechanization tools can cause soil compaction slowly, one of which is characterized by a small permeability value [13].Point H before the tillage had the highest permeability, which was 15.42 cm/hour, classified as rapid permeability, then decreased drastically after tillage to 0.48 cm/hour and categorized into slow permeability value.
Based on the graph in Figure 2 As we expected, there were variations in growth at each observation point regarding the number of stems, stem height, and plant diameter (Figure 3).Plot G is the observation point with the highest number of sugarcane stalks, and point E with the least number of stalks.For plant height, plot G also has the highest stem height compared to other observation points.For plant diameter, the average for the whole plant has the same diameter ranging from 2-2.5 cm.When viewed from the east, plots A, D, and G are in the east, which means they are exposed to sunlight first.This value is consistent with the theory that the length and diameter of cane internodes are affected by humidity, nutrition, and temperature.Sugar cane with short internodes reflects stunted growth [15].Tillers will form when the sugar cane enters the age of 2 months and last up to 120 days after planting.Several factors support the formation of tillers, such as variety, light, temperature, and soil moisture.Light is the most critical factor.Adequate light will produce vigorous vegetative shoots.30 o C is the ideal temperature for the germination phase, and temperatures below 20 o C will slow down the formation of sugar cane tillers.Early saplings produce thicker and heavier culms, while those formed late die or remain short and immature at harvest time.One sugarcane shoot will produce about six to eight tillers [16].Only 4-6 tillers per sugarcane shoot were formed at the study site.The tillers formed are still below the average sugarcane tillers that should be.This result dramatically affects the sugar cane production in Takalar.In addition, the height of the sugar cane generally ranges from 250 to 400 cm with a diameter of 2-5 cm.The graph in Figure 4 shows that the height of the tallest sugarcane stalk is only about 204 cm, with the largest diameter of only 3 cm.This measure indicates that the growth of sugarcane in Takalar is stunted.

Conclusion
Sugarcane growth is affected by several climate factors, including rainfall, temperature, soil conditions, and light.Soil conditions in Takalar indicate that the soil in the sugar cane fields is very vulnerable to rainfall.A low soil permeability value results in the very slow movement of water in the soil, so the soil becomes stagnant during high rainfall, and during drought, the soil cannot store water supply for plants.These factors then affect plant growth so that the number of tillers that grow is small, the plant height is short, and the plant diameter is small.
occurred at the beginning of sugarcane planting, namely in November 2021, a monthly average air temperature of 28.36 o C. With low rainfall of around 5.35 mm and high temperatures, it causes drought on the land.

Figure 2 .
Figure 2. Monthly average precipitation (P), monthly mean temperature (T), and number of rainy days (Rd) obtained from Takalar Sugar Factory station.

Figure 3 .
Figure 3. Soil permeability values before and after tillage.

Figure 4 .
Figure 4. Sugarcane productivity every 7.5 meters in one hectare of land on the duration of planting to harvest.(a) number of the stem (NS), (b) stem height (SH), and (c) diameter