This study was conducted at the two villages Pawaingyoe and Kokkokhahla of Pyawbwe Township in Mandalay Region, CDZ of Myanmar during post-monsoon season in 2019 and 2020. Pyawbwe is located at latitude 20.5977˚N, longitude 96.0494˚E, 198 meters above sea level. Pawaingyoe (N20.64682˚, E96.22815˚) and Kokkokhahla (N20.55128˚, E95.96853˚) are located in eastern and west-southern parts of Pyawbwe, respectively. Total N and available N were slightly higher in Pawaingyoe than Kokkokhahla for both years (Table 1). In Pawaingyoe, the values of ECEC, OC and NO 3 − -N were higher, but saturated hydraulic conductivity values in all soil depths were lower than these values in Kokkokhahla (Table 2). Generally, Pawaingyoe was clay loam soil texture whereas Kokkokhahla was sandy loam soil texture.

In 2019, following mung bean, cotton seeds were sown in the experimental plots

on 27 July in Pawaingyoe and on 4 August in Kokkokhahla. In 2020, the land was fallowed in summer and cotton seeds were sown in the same experimental plots on 27 July in Pawaingyoe and on 1 August in Kokkokhahla. The experimental plots were laid out in randomized complete block (RCB) design with four replications. Ngwechi-6 cotton cultivar was used and the cotton plants were grown with the spacing 0.75 × 0.75 m². The total experimental area was 1147.44 m² containing 24 plots. The area of each sub plot was 6.75 × 6.75 m² having 9 rows and 9 hills in each row. Six levels of N rate source as urea (T1 = 0, T2 = 60, T3 = 90, T4 = 120, T5 = 150 and T6 = 180 kg N ha⁻¹) were used as treatments and N was applied as split dose, i.e., 20% at sowing, 40% at squaring, 40% at flowering. For all treatments triple super phosphate (60 kg P₂O₅ ha⁻¹), muriate of potash (60 kg K₂O ha⁻¹), zinc sulphate (15 kg ha⁻¹) and borax (5 kg ha⁻¹) were applied at basal. Cotton seeds were treated with dozar 20% WP 0.25 kg ha⁻¹ to prevent from sucking pests at the seedling stage and field managements were implemented as the usual cultural practices. Thinning was done 18 days after emergence (DAE) and leaving two plants per hill. Pest control and other management practices were done as necessary. Management was taken across all the treatments in each experimental site. The same experimental design, used cultivar, plot size, treatments, all field management practices, data collections and data calculations were carried out for both sites in each year. A total of four pickings were done in 2019 for both sites. In 2020, four pickings were done in Pawaingyoe and only three times of pickings were done in Kokkokhahla.

The data obtained from this test were statistically analyzed with Statistix 8 software and the treatment means were done using Least Significant Difference (LSD) test at 5% level of significance.

During the cotton growing season, Pawaingyoe received a total of 387 mm rain-fall in 2019 and 319 mm in 2020, while Kokkokhahla received a total of 515 mm in 2019 and 298 mm in 2020. The rainfall in 2019 at both sites was higher than 10-year average and the rainfall in 2020 at both sites was lower than 10-year average and 2019. The minimum and maximum temperatures ranges during 2019 and 10-year average were similar in both sites. In 2020 at both sites, the minimum and maximum temperatures values were slightly higher than that of 10-year average and 2019 (Figure 1).

Each year, Pawaingyoe (clay loam) had higher amount of DUL, CLL and PAWC values than Kokkokhahla (sandy loam) in all soil depth (Figure 2). In 2019, total PAWC (up to depth of 150 cm) of these soils were 250.78 mm in Pawaingyoe

and 150.84 mm in Kokkokhahla. In 2020, total PAWC (up to depth of 150 cm) of these soils were 227.00 mm in Pawaingyoe and 132.86 mm in Kokkokhahla. Each year in both sites, the highest amount of available water capacity was observed in the upper soil layers 0 - 50 cm compared to deeper soil layers 50 - 150 cm of soil profile.

The differences in soil water content within the soil profile of Pawaingyoe and Kokkokhahla were caused mainly due to difference in soil texture (Table 2). Owing to the association between clay content and soil porosity, soils with higher clay content have greater soil water storage capacity than sandy soils. Soil texture affects the water content and drainage ability of soils [18]. Another reason may be due to the effect of organic matter content. Since, Kokkokhahla soil had lower OC% than Pawaingyoe. PAWC is positively related to soil organic matter. Soil organic matter enhances soil water retention because of its hydrophilic nature and its positive influence on soil aggregate formation [19]. It has been recognized that decreases in soil OC could reduce PAWC and soil fertility [20]. In comparing BD of each site, Pawaingyoe (clay loam) had lower amount of BD than Kokkokhahla (sandy loam) in all soil depth (Figure 3) and BD increased with soil depth in both sites.

Each year, there were significant differences in seed cotton yield and all yield components among the treatments in both sites (Table 3). The seed cotton yields and yield components from the plots applied with N fertilizer were significantly higher than that of plot without N fertilizer in both sites in both years. In Pawaingyoe, the seed cotton yield varied from 1386 to 2364 kg ha⁻¹ in 2019 and from 1027 to 1607 kg ha⁻¹ in 2020. The maximum values of seed cotton yield and all of yield components in Pawaingyoe was obtained from 60 kg N ha⁻¹ (T2) in 2019 and 90 kg N ha⁻¹ (T3) in 2020. In 2020 at Pawaingyoe, the maximum yield and all of the yield components were produced by T3 which was not significantly different from other N treatments, T2 through T6. According to this result, there was distinct response to N at T2 in Pawaingyoe during both experimental years. It may be assumed that further additional N rates were not necessary to increase seed cotton yield. These results are supported by [21] who reported that N influenced seed cotton yield and decrease in seed cotton yield was recorded when N was applied above the optimum level.

In Kokkokhahla, the seed cotton yield varied from 1088 to 1976 kg ha⁻¹ in 2019 and from 648 to 970 kg ha⁻¹ in 2020. The maximum yield and all of the yield components in Kokkokhahla were obtained from 120 kg N ha⁻¹ (T4) and 90 kg N ha⁻¹ (T3), in 2019 and 2020, respectively. In both years, all the treatments in Pawaingyoe produced higher seed cotton yield and yield components than Kokkokhahla. The seed cotton yield and all the yield components parameters in both sites during 2020 were lower than that of 2019, particularly maximum yield of Kokkokhahla decreased 50.9% yield of 2020 than 2019, while Pawaingyoe decreased only 32% yield of 2020 than that of 2019. This may be due to the poor performance of the cotton under low PAWC resulting from unfavorable rainfall condition. Soils with higher PAWC are more resistant on low rainfall than soils with lower PAWC.

Means followed by the same letter in each column are not significantly different at 5% LSD; ** = significant at 1% level; * = significant at 5% level; ns = non-significant.

Agronomic NUE evaluates N fertilizer investment benefit and it is linearly related to specific seed cotton yield and N fertilizer prices. Understanding how NUE changes with N fertilization rates will assist producers in N management decisions that affect both the profitability and N impact on the environment [22]. Each year in both sites, NUE was significantly affected by N application and NUE gradually decreased with increasing N rate, more than 60 kg N ha⁻¹ at Pawaingyoe and more than 90 kg N ha⁻¹ at Kokkokhahla (Figure 4). According to Fan [23], who reported the low nutrient use efficiency may be attributed to fertilizer overuse and high nutrient loss. Owing to the law of diminishing returns, the yield per unit N supply declines with increasing N supply [24]. The highest values of NUE in Pawaingyoe were obtained from 60 kg N ha⁻¹ (T2) with the value 16.31 in 2019 and 8.77 in 2020. In Kokkokhahla, the highest values of NUE was obtained from 90 kg N ha⁻¹ (T3) with the value 7.76 in 2019 and 3.58 in 2020. In both years, NUE values of all treatments were lower in Kokkokhahla

than Pawaingyoe. Fertilizer use efficiency in the coarse-textured permeable soils is very low due to excessive N losses [25]. The decrease in NUE at higher N rates was because the increase in yield was lower than the increase in N rate. This is probably because yield increase with N is not linear and at higher N rate there was no yield increase. NUE of both sites in 2020 were lower than that of 2019, particularly in Kokkokhahla. The reason might be due to low rainfall in 2020 than 2019 this led to low soil water content, and consequently low N availability (Figure 1).

In 2019, there was a significant N application effect for fiber strength at Pawaingyoe, while there was a significant N application effect for both fiber length and strength at Kokkokhahla (Table 4). At Pawaingyoe, T2 gave maximum fiber strength (8.23 lb mg⁻¹), while at Kokkokhahla T4 gave greater fiber length (28.32 mm), fiber strength (8.23 lb mg⁻¹) than other treatments. However, non-significant N application effect for all fiber qualities in 2020 at both sites. The reason might be low rainfall in 2020 leading to poor soil moisture. Consequently, fiber quality parameters were not affected by N application in 2020. Fiber properties of cotton may be affected by other factors such as, temperature, humidity, soil moisture [26] and fertilizers [27].

This study highlighted that PAWC and the variability of seasonal rainfall may be a major source of variation on the response of cotton by N application in respective site. In both years, the growth and yield of cotton were higher in Pawaingyoe, because of high PAWC in Pawaingyoe and thus greater level of water availability during cotton development. The results are consistent with findings of [28] who reported that soils with high PAWC provided a larger buffer to store water from

Means followed by the same letter in each column are not significantly different at 5% LSD; ** = significant at 1% level; * = significant at 5% level; ns = non-significant.

variable rainfall and to supply it to crops during dry periods and therefore were less affected by rainfall decreases compared to soils with low PAWC. Kokkokhahla (low PAWC) has sandy loam texture and cotton grown on this soil was more responsive to N than clay loam texture soil of Pawaingyoe (high PAWC), probably because organic N reserves are lower, the soil is more often dry, and nitrate N cannot be held in the profile against leaching. Soils with low PAWC are typically sandier and crops grown on these soils are more responsive to N than finer textured soils [29].

When comparing the two sites, Pawaingyoe (high PAWC) was found to be better in terms of yield components, yield and NUE than Kokkokhahla (low PAWC) in both years, as high PAWC can lead to more water use and the availability of water to crops. When comparing the two years, the more favorable growing seasons rainfall conditions in 2019 (wet year) resulted in much higher growth and yield than 2020 (dry year) in both sites and more response to N application was observed in wet year than dry year.