Response of Corn Varieties under Saturated Soil Culture and Temporary Flooding in Tidal Swamp

Corn is one of the important food crops and feeds in the world. Conversion of agricultural land into non-agricultural land is one of the major causes of the decline in corn production. Saturated soil culture (SSC) is a cultivation technology that gives continuous irrigation and maintains water depth constantly and makes soil layer in saturated condition. This technology can prevent pyrite oxidation in the tidal swamp. This research aimed to study the effect of temporary fl ooding under saturated soil culture on the growth and productivity of corn. The research was conducted at Karya Bhakti village, Rantau Rasau, Tanjung Jabung Timur, Jambi Province, Indonesia. The experiment used a split plot design with three replications. The main plot is fl ooding condition, consisted of 1) saturated soil condition continuously, from planting until harvesting time (as control), and 2) saturated soil condition from 0 to 10 DAP (Days after Planting) + fl ooding from 11 to 13 DAP + saturated soil condition from 14 to 28 DAP + fl ooding from 29-31 DAP + saturated soil condition from 32 DAP until harvesting time. The subplot is corn variety, “Sukmaraga”, “Bisma”, “Pioneer 27”, and “Bima 20”. “Pioneer 27” had the highest productivity of 9.33 t.ha-1. Corn varieties with moderate tolerance to temporary fl ooding were “Sukmaraga” and “Bisma”, whereas “Pioneer 27” and “Bima 20” are sensitive to fl ooding.


Introduction
Corn is one of the important food crops besides rice and soybeans, as well as feeds. Corn productivity in Indonesia in 2016 was 5.30 t.ha -1 dry shells, whereas the corn consumption was 20 million tons (Suwandi, 2017). Java island is the largest national corn producing area (Komalasari, 2018). Corn productivity in Indonesian islands outside Java is still low, i.e. 4.67 t.ha -1 , compared to production in Java, i.e. 5.67 t.ha -1 . The harvested area of corn in 2009 was 4.16 million ha, but in 2015 it had decreased to 3.79 million ha (BPS, 2017). Java harvested area of corn in 2015 (2.99 million ha) is four times as large as Sumatera (0.75 million ha).
The decrease of the corn harvested area was due to the conversion of agricultural land to non-agriculture (Kementan, 2015). As a result, the import of dry shelled corn increased by 0.5 million tons in 2016 compared in 2015 (Kemenperin, 2016). One of the ways to increase corn productivity is by growing corns in sub-optimal agricultural land. The utilization of suboptimal land has important important roles to support sustainable agriculture.
The tidal swamps are sub-optimal lands that are widely found in Indonesia; it is estimated to be around 9.53 million ha (Arsyad, Saidi and Enrizal, 2013). Ismail et al. (1993) stated that tidal swamp lands have agricultural potential, including the tidal swamps located in Jambi Province. The tidal swamp area in Jambi is estimated to be 684,000 ha, and about 30 % (246,481 ha) can be developed into agricultural land (BPTP, 2017). Four types of tidal swamps have been identifi ed. Type A tidal swamp is fl ooded by large and small tide, type B by small tide, type C and D is not fl ooded but has a water depth < 50 cm and >50 cm, respectively (Ar-Riza and Alkasuma, 2008). The types of tidal swamp that could be used for corn production is type B, C, and D (Ghulamahdi et al., 2009;Adam et al., 2013).
The problems in using tidal swamp for agricultural land are the occurrence of temporary fl ooding, high salinity, and oxidation of pyrite or iron oxide, which is very toxic to plants (Noya et al., 2014;Sulistiyani and Putra, 2014). Temporary fl ooding occurs when the rise of water caused by gravitational forces of the moon meets with the high rainfall, resulting in an overfl ow of river water and caused fl ooding in the tidal swamp land of up to 3 hours. On the other hand, pyrite oxidation occurs when tidal swamp land is dry and pyrite will be oxidized to toxic form Fe(OH) 3 (Ghulamahdi et al., 2006;Lubis et al., 2016).
Saturated soil culture (SSC) is a cultivation technology that gives continuous irrigation and maintains water depth constantly and makes soil layer in saturated condition. SSC can reduce pyrite oxidation thus support corn growth on tidal swamp (Ghulamahdi, 2017). Selection of corn varieties to grow on tidal swamps affects its productivity. Corn productivity on tidal swamp was still low, i.e. 2.21 t.ha -1 (Jumakir and Erizal, 2009). However, the research of temporary fl ooding in tidal swamps and its effects on corn production is still limited. This study aims to evaluate temporary fl ooding and SSC on the physiology, growth, and yield of corn, and determine tolerant and high yielding corn varieties to grow in the type B tidal swamp.

Experimental Site
The experiment was carried out on tidal swamp type B in Karyabakti Village, Rantau Rasau District, East Tanjung Jabung Regency, Jambi Province, Indonesia, from April to September 2018.

Treatments
The experiment was carried out using a split plot design with types of fl ooding as main plots, and corn varieties as sub-plots. Types of fl ooding consisted of saturated soil culture (SSC, control), and SSC at 0 to 10 days after planting (DAP) + fl ooding at 11 to 13 DAP + SSC at 14 to 28 DAP + fl ooding at 29 to 31 DAP + SSC at 32 DAP until harvest. Four corn varieties, "Sukmaraga", "Bisma", "Pioneer 27", "Bima 20", were tested, so there were 24 experimental units in total. Each experimental unit consists of 2 m x 9 m plots that were surrounded with 30 cm width x 50 cm depth trenches. Irrigation water was applied continuously from planting until harvest with a water depth of 30 cm below the soil surface ( Figure 1). Temporary fl ooding (TF) was created by supplying irrigation to a water level of 5 cm above the soil surface for three hours ( Figure 2). Dolomite (2 t.ha -1 ) and SP-36 (300 kg.ha -1 ) were applied two weeks before planting. Urea (150 kg.ha -1 ) was applied twice, at planting and at 30 DAP, whereas KCl (100 kg.ha -1 ) was applied at planting. Corn crops were sprayed with 15 g.L -1 of Urea with a volume  water spray of 400 L.ha -1 weekly at two to fi ve weeks after planting (WAP). Corn seeds were treated with insecticide fi pronil (50 g.L -1 ) prior to planting, with the spacing of 100 cm x 20 cm (20 plants per plot). Crops were harvested once they reached their physiological maturity, indicated by the presence of 'black layer' on the corn kernels.
Measurement of corn growth consisted of plant height, the number of leaves, stem diameter, leaf area, leaf area index (LAI) on fi ve sample plants per plot. Root volume and root length were measured at four and eight 8 DAP on one sample plant per plot. Physiological measurement consisted of relative growth rate (RGR) and net assimilation rate (NAR), measured on one sample plant per plot, at 4 to 6 and 6 to 8 WAP using formulas from Gardner et al. (1991) as follows: where ln is natural logarithm, W 1 is dry weight at t 1 , W 2 is dry weight at t 2 , t 1 is time one, t 2 is time two, A 1 is Leaf area at t 1 , and A 2 is leaf area at t 2 .
Stomatal density (SD) were measured on the 5 th leaf at 3 WAP and the 7 th leaf at 5 WAP on two plant samples per plot. A clear nail polish was used and spread on abaxial leaves, left to dry, and a strip of clear sticky tape was placed over the nail polish. The sticky tape was then peeled off and the leaf section was placed on a microscope slide. Observation was made using 400 x magnifi cation. SD was determined by equation from Xu and Zhou (2008) as follows: Where π = constant (3.14) and r 2 (radius of fi eld of view on 400x magnifi cation).
Leaf greenness were determined on 5 sample plants per plot using Greenness Leaf Colour Chart (Balitsereal, 2007). Measurement was made at three points of each leaf, i.e. edge, midle, and base of the 5 th leaf at 4 WAP, and of the 7 th leaf at 6 WAP, then the values were averaged (Balitsereal, 2007).
Corn yields were measured on fi ve sample plants per plot. Yield components consist of cob weight, cob length, cob diameter (measured in the middle of each cob), and number of rows per cob, number of kernels per row, the weight of dry seed per cob, 100-seeds dry weight, and productivity.
The sensitivity index (SI) determined by equation described in Fischer and Maurer (1978): where SI is sensitivity index, Y p is mean of productivity from all varieties, Y is mean of productivity on SSC, X p is average productivity from all varieties in TF, X is average productivity from all varieties in SSC. The criteria of tolerance is SI < 0.5 is tolerant, 0.5 < SI < 1.00 is moderate-tolerant, and SI > 1.00 is sensitive. Data was analyzed using SAS 9.4 software (SAS Institute Corp); signifi cant differences between means were further tested using Tukey test with signifi cance level of 5%.

Corn growth
There were interactions between types of fl ooding and corn variety in affecting corn growth at 4 WAP ( Table 1).
Types of fl ooding and corn variety interacted in  (Table 1). Corns of all varieties that had temporary fl ooding were shorter; the decrease in plant height was up to 26% and had shorter roots (Table 1). "Pioneer 27" was the tallest compared to the other varieties (Table 1). The high levels of Al (Aluminum) and Fe (Iron) in tidal swamps inhibited corn growth (Panda et al., 2009;Sutoro, 2012). In addition, fl ooding can cause increasing availability of Al and Fe in the soil surface, so their levels had started to be toxic to the crops. Research conducted by Roberto (2000) stated that aluminum stress tends to reduce the growth of sensitive corn varieties.
Temporary fl ooding did not affect the number of leaf per plant and root volume at 4 DAP ( Table 2). Stem diameter of the crops in temporary fl ooding treatment decreased by 17% compared to SSC. Different corn varieties had different stem diameter in response to the types of fl ooding. "Sukmaraga" had the largest stem diameter, but was not signifi cantly different from by "Pioneer 27" at 4 WAP. According to  temporary fl ooding resulted in the decrease of corn stem diameter.
Flooding signifi cantly reduced stem diameter, root length, and root volume at 8 DAP (Table 3). Corn with SSC has the largest stem diameter, longest roots, and the largest root volume compared to those with temporary fl oding. Different corn varieties have different vegetative characters, except for leaf area and LAI. "Pioneer 27" has the fastest vegetative growth whereas "Bisma" had the slowest. LAI values were > 2.5 in all treatments. Corn plants that have LAI between 2.5 to 5 have maximum dry matter and high productivity potentials (Goldsworthy et al., 1974).
At 8 DAP corns possibly had adapted to tidal swamp environment (Table 3). Accumulation Al and Fe might have occurred more frequently in the temporary fl ooding an inhibited growth of roots and stems. Roots became shorter so they absorb less nutrients from the soil, especially phosphorus, which has essential functions in cell division in plants (Ghulamahdi et al.,   Gupta et al., 2013).

Effects of Flooding Treatment on Corn Physiology
Types of fl ooding or corn variety alone signifi cantly affected stomatal density at 3 WAP, Leaf greenness at 4 WAP, RGR at 6 to 8 WAP, and NAR at 6 to 8 WAP (Table 4). Types fl ooding and corn variety interacted in affecting stomatal densities at 5 WAP, leaf greenness at 6 WAP, and RGR 4 to 6 WAP ( Table 5).
The temporary fl ooding treatments increased RGR and NAR at 6 to 8 WAP, and decreased leaf greeness at 4 WAP. Different corn varieties demonstrated differences in leaf greeness at 4 WAP, RGR at 6 to 8 WAP, and NAR at 6 to 8 WAP. "Bima 20" has the highest RGR and NAR at 6 to 8 WAP compared to "Pioneer 27", but it was not signifi cantly diferrent from RGR and NAR of "Sukmaraga" and "Bisma".
The reduced values of green color intensity due to fl ooding is an indicator that the crops were nitrogendefi cient (Wang et al., 2012). Balitsereal (2007) reported that corn with leaf greeness value of <4.25 are nitrogen defi cient. The RGR and NAR values were higher in temporary fl ooding than in to SSC. We assumed that the growth and assimilation rate of the plants that had been returned to the optimal condition (SSC) will increase, resulting in speedy recovery.
"Pioneer 27" with temporary fl ooding had the lowest stomatal density and leaf green intensity values (Table  5). "Bisma" had the highest RGR value at 4-6 WAP in the SSC, whereas with temporary fl ooding "Bisma" had the lowest Leaf Greenness. Leaf Greenness of the hybrid varieties in temporary fl ooding at 6 WAP was > 4.5, whereas in the composite varieties it was < 4.5. It was likely that the nitrogen absorption is more effective in hybrid varieties compared to that of the Note: values followed by the same letters in the same column are not signifi cantly different based based on Tukey test α=5%. SSC= saturated soil culture, TF = temporary fl ooding, RGR = Relative growth rate, NAR = net assimilation rate, WAP = weeks after planting. Note: the values followed by the same letters in the same column were not signifi cantly different based based on Tukey test α=5%; SSC = saturated soil culture, TF = temporary fl ooding, RGR = relative growth rate, WAP = week after planting composite varieties. RGR value of composite varieties ("Sukmaraga" and "Bisma") in TF was higher than that of the hybrid variety ("Pioneer 27"). It is possible that early mature varieties had higher RGR than the late mature variety ("Pioneer 27"), even though both of them were under stressed environment.

Yield
The corn yield components were signifi cantly affected by the fl ooding treatment (Table 6) and its interaction with corn variety (Figure 3). Flooding affected the number of seeds per row, cob weight, and 100-seed dry weight. Corn with SSC treatment had the highest yield components.
"Pioneer 27" had the best cob characters compared to the other varieties, except cob length and 100-seeds dry weight. The cob length of "Sukmaraga", "Pioneer 27", and "Bima 20" lengths similar. Number of rows per cob, 100-seeds dry weight and number of kernels per cob row in "Sukmaraga", "Bisma", and "Bima 20" were similar.
The interaction between types of fl ooding and corn variety signifi cantly affected yields. "Pioneer 27" with SSC treatment had the highest cob weight (289.09 g), 100-seed dry weight per plant (228.04 g), and productivity of 9.33 t.ha -1 respectively. Except for Pioneer, the productivity of the corn varieties with SSC treatment was ± 6 t.ha -1 , whereas in "Bisma" it was only 5.87 t.ha -1 . On the other hand, "Pioneer 27" in the temporary fl ooding had the highest productivity compared to the other variety in this treatment. The average corn productivity in the tidal swamp is about 2 to 3 t.ha -1 (Jumakir and Endrizal, 2009;Nazemi et al., 2012) Combination of genetic and environmental factors determines crop productivity. Ghulamahdi (2017) reported that even though the crops are in a stressfull condition, SSC can suppress pyrite oxidation, so the soil pH in the root zone do not become acidic. Therefore, toxic elements including Fe and Al were not available, whereas the essential macronutrients become available. Sagala (2015) stated that the intensity of solar radiation on tidal swamp could reach 1,063 w.m -2 in August. High light intensity promotes photosynthesis to the maximum rate. Therefore, supported by the availability of water on the tidal swamp and the availability of nutrients from fertilization, the corn productivity on tidal swamps can be potentially high.

Sensitivity Index
The sensitivity index (SI) of a variety to temporary fl ooding is determined by its productivity after the fl ooding treatment. The composite varieties, "Sukmaraga" and "Bisma", have an SI value of 0.71 to 0.77, so they were grouped as moderately tolerant varieties. The hybrid varieties "Pioneer 27" and "Bima 20" have an SI value of 1.05 to 1.32, so they were grouped as sensitive varieties (Table 7).
The intensity and duration of fl ooding greatly affected the corn yields. Ren (2014) stated that the corn is very sensitive to fl ood in the V3 stage, which is indicated by the rapid growth of rooting system below the ground rather than the canopy growth. According to Suwarti et al. (2013) corn hybrid varieties are generally sensitive to fl ood during early vegetative growth; fl ooding at this stage would reduce corn productivity. In addition, Marschner (2012) reported that composite varieties are more likely to be tolerant than high yielding varieties. "Pioneer 27" had the highest productivity compared to other varieties, even though the crops were fl ooded.

Conclusion
Different corn varieties demonstrated different growth, physiology, and yields under different types of fl ooding. All growth variables were the highest in the SSC treatment, except for RGR and NAR at 6 to 8 WAP. "Pioneer 27" had the highest productivity of 9.33 t.ha -1 . "Sukmaraga" and "Bisma" were the most tolerant varieties to temporary fl ooding treatment, whereas the "Pioneer 27" and "Bima 20" are the sensitive varieties. "Pioneer 27" in temporary fl ooding treatment had the highest productivity of 7.31 t.ha -1 .