Effects of Superabsorbent Polymer, Potassium Sulfate, and Manure on Yield and Date Bunch Fading Disorder Control of "Mazafati" Date Palm Cultivar

The date bunch fading disorder causes huge loss on farmers' incomes and damages to economy of date producing regions. Thus it is important to find a way for controlling the disorder or reducing its economic damages. It seems that the water losses of the tree under critical environmental conditions, such as high temperature and very low air relative humidity, cause date bunch fading disorder especially when is accompanied by regional warm wind. According to the scientific literatures, the use of different covers on bunches, high-frequency irrigation, foliar application of mineral nutrients and anti-transpiring substances, and soil mineral fertilization can affect date palm bunch fading disorder. Superabsorbent polymers have great capability for storage water and can be used in soil to improve its water retention and increase soil available water under drought conditions. On the other hand, potassium has important roles in metabolism of carbohydrates, plant water relations as the major element in action mechanism of stomata, and plant water osmotic potential. Organic matter can also improve soil physical properties, i.e., soil structure and soil available water as well as soil fertility and bioavailability of mineral nutrients. Because of mentioned roles of these three factors, the effects of them on date palm bunch fading disorder were investigated in this research.

The effects of superabsorbent, potassium fertilizer, and manure on yield and date bunch fading disorder of "Mazafati" date palm cultivar were investigated in Jiroft, Kerman province, south of Iran. An experiment was conducted in factorial randomized complete block design. The factors were included superabsorbent polymer A200 in 0 (S1), 200 (S2), and 300 (S3) g.tree-1 levels, potassium sulfate fertilizer in 0 (K1), 2 (K2), and 3 (K3) kg.tree-1 levels, and cow manure in 0 (O1), 65 (O2), and 130 (O3) kg.tree-1 levels. Treatments were applied in February in three blocks and harvest was done at the first half of August. The yield of intact fruits, the yield of dried and dropped fruits (collected in an elastic silicone wire cloth cover), and total yield were determined at the harvest time and date bunch fading disorder was calculated as weight percentage (the dried fruits weight was divided by the total fruits weight and multiplied by 100, in each plot). Weight, diameter, and length of fruits were measured and determined from a random sample containing 30 intact fruits per each plot (a tree). Statistical analysis was done by IBM SPSS Statistics version 25.

According to the results, the block had no significant effect on any of studied parameters, on the other hand, the results showed significant effects of all three factors on all of the measured parameters including percentage of date bunch fading disorder, total fruits yield, intact fruits yield, fruit weight, fruit diameter, and fruit length, except fruit length by the manure factor, by ANOVA at the 0.01 level. Three factors interaction significantly affected only the fruit characteristics including weight, diameter, and length of fruit. About the intact and total fruits yield and date bunch fading disorder, interactions between superabsorbent and two other factors were statistically significant. The highest means of intact fruits yield were observed in S3K3 and S3O3 treatments (28.9 and 28.7 kg.tree-1) increased by 98% and 93% compared to S1K1 and S1O1 treatments, respectively; and they were also significantly higher than those of all other treatments. The maximum means of total yield were found in S3K3 and S3O3 treatments (35.0 and 26.8 kg.tree-1) increased by 33% and 28% compared to S1K1 and S1O1 treatments, respectively. The mean percentage of date bunch fading disorder was significantly decreased by increasing the levels of superabsorbent, potassium fertilizer, and manure factors in interactions between superabsorbent and two other factors (SK and SO interactions), thus the lowest mean of date bunch fading disorder percentage in both interactions was found in third levels of each factor (S3K3 and S3O3 treatments), decreased by 60% and 63% compared to S1K1 and S1O1 treatments, respectively. The lowest and the highest mean of fruit weight, fruit diameter, and fruit length parameters were observed in S2K1O3 and S3K3O3 treatments, respectively. Negative significant correlations were found between percentage of date bunch fading disorder and total fruits yield, intact fruits yield, fruit moisture, fruit weight, fruit diameter, and fruit length, while the last six parameters had positive significant correlations with each other. In addition to common positive effects of three factors on water supply improvement, they can influence plant progress in different ways, such as carbohydrate metabolism and activation of some enzymes by potassium, and increasing of mineral nutrients availability and soil microbial activities by organic matter and manure. Therefore, these three factors could have some positive interactions on their effects on control of the disorder, increasing the yield, and improvement of weight and size of fruit. An observed decrease in weight and size of fruit by using 2nd level of superabsorbent and 3rd level of manure can be resulted from significant decrease in percentage of disorder and finally competition between safe fruits for potassium in carbohydrate metabolism and so on.

According to the results of this research, applying of superabsorbent polymer (300 g.tree-1), potassium fertilizer (3 kg.tree-1), and manure (130 kg.tree-1) together can be recommended to improve qualitative parameters of date palm fruits (weight, length, and diameter). Applying the 3rd levels of these factors together can also control date bunch fading disorder cv. Mazafati, and increase the economic income because of qualitative improvement of fruits.