Abstract: Present studies were conducted to evaluate the effect of fertilizer application at different times of the year on the productivity of kinnow. 40 kg rottened farm yard manure, 1 kg urea, 4 kg single supper phosphate and 1 kg sulphate of potash per plant was applied at three different times i.e., in January, April and July. Application in January improved the number of fruits, fruit size, weight of fruit and juice contents during 1997-98. TSS and juice percentage was not affected by any treatment. The same trend for effect of fertilizers was also observed during 1998-99 with a difference only that juice percentage was also affected with fertilizer treatment and increased when the fertilizer was applied in January. When the fertilizers were applied in April or July, no improvement was noted and the results were similar to or worse than control.
Introduction
Kinnow (Citrus reticulata Blanco) is an important member among citrus fruits. It is the heaviest bearer than any other citrus fruit. It is very much liked by all sorts of people due to its excellent taste, dietary values, rich in vitamin-C, large amount of juice and melting juice vesicles. Citrus occupies the first position in fruit industry with regard to its area and production in Pakistan and kinnow shares the major part of this area and production. Area under citrus is 196.1 thousand hectares, out of which kinnow is planted on 17.9 hectares (Anonymous, 1998).
Unfortunately, the production from kinnow orchards is very low than standard. There are so many reasons for this low yield but fruit drop, alternate bearing insufficient plant protections and non judicious use of fertilizers are major limitations. Fertilizers are being used by the growers at any time of the year without knowing the proper time at which the fertilizer may improve the crop more effectively and its impact on yield.
A fertilizer trial was carried out on 7 year old mandarin (Citrus reticulata) cv. Local. N at 0, 50 or 100 g/plant and P2O5 and K2O each at 0 or 50 g/plant were applied in the last week of January and last week of April each year. The highest yield and the greatest plant spread (4.4 m N-S and 4.6 m E-W) were obtained with 100 g N + 50 g P2O5 + 50 g K2O applied in January. The largest fruit weight (147 g) was also obtained with this treatment. The stem girth was largest with 50 g N + 50 g P2O5 + 50 g K2O. The treatments had no significant effect on fruit diameter and quality (Sharma and Azad, 1991). An experiment was conducted on satsuma mandarin to observe the effect of fertilizers on fruit quality and yield. Soil OM content was 1.02-1.13%. N was applied at 0.038-0.045%, P2O5 at 0.030-0.024% and K2O at 0.88-1.02%. Different combinations and rates of N, P, K and lime were applied at different times. Results showed that P application had no effect on yield but the combined application of NPK before the initiation of new growth in February increased yield by 28.5% but fruit acidity was increased. Applying lime powder at 2250 kg/ha increased yield by 37.2% and had a good effect of fruit quality (Meng et al., 1992). In experiments with 18 year old Weizhang satsuma mandarin trees, Biquan (a foliar applied fertilizer, produced in Taiwan) was applied at different times and at different concentrations. Shoot growth, leaf chloroplast content and the photo synthetic rate of the leaves were measured. Fruit quality was also evaluated. Results showed that application 1-3 times (at the pre-flowering stage, at the time of physiological fruit drop and during the period of fruit let swelling), all had positive effects on the shoot growth, leaf chloroplast content and photosynthetic rate. The soluble solids content of the fruits of sprayed trees was increased by 1.5-1.9% and the fruits were of better colour and had a richer flavour with increased yield (Shi et al., 1992). Different combinations of NPK were applied before flowering, after fruit setting and during fruit bud differentiation. It was noted that yield, fruit size and quality was improved with the application before flowering (Ronetz, 1993).
Keeping in view the above mentioned facts this project was initiated to find the effect of time of fertilizer application on kinnow productivity.
Materials and Methods
Present studies were carried out at Horticultural Research Station, Dera Ghazi Khan during 1997 to 1999. There were three treatments and four replications thus twelve plants of kinnow were selected for the studies. One more plant was selected to serve as control. The plants were growing under similar agroclimatic conditions and were uniform in size and age. The age of the plants was round about 10 years. Various treatments were as under:
| T1 | = | Control |
| T2 | = | Application of fertilizer in January |
| T3 | = | Application of fertilizer in April |
| T4 | = | Application of fertilizer in July |
The dose of fertilizer used per tree was as:
| (i) | Farm yar manure = 40 kg |
| (ii) | Urea = 1 kg |
| (iii) | SSP = 4 kg |
| (iv) | SOP = 1 kg |
The farm yard manure and fertilizers were applied as a single dose as combined application. Same dose was repeated three times a year i.e., January, April and July. In case of January and April treatments, nitrogen was applied in two split doses. Data on the following parameters were recorded:
| 1 | Number of fruits |
| 2 | Fruit size (cm)2 |
| 3 | Average weight per fruit (g) |
| 4 | T.S.S. |
| 5 | Juice contents |
| 6 | Juice percentage |
The experiment was laid out according to the randomized complete block design. The treatment means were compared for their significance by Duncan’s Multiple Range test with the method described by Steel and Torrie (1980).
Results and Discussion
Nearly same trend was noted in the results of 1997-98 and 1998-99 for various reproductive characters.
| Table 1: | Effect of time of fertilizer application on the productivity of kinnow (Citrus reticulata Blanco.) in 1997-98 |
| Table 2: | Effect of time of fertilizer application on the productivity of kinnow (Citrus reticulata Blanco.) in 1998-99 |
Some factors of fruit were affected as a resulted of fertilizer application showing significant difference while others remained unaffected. The factors which gave significant difference are discussed as under:
Number of fruits per plants: Table 1 and 2 depict significant results for various treatments. T2 got the highest position by producing 493.3 fruits in 1997-98 and 657.7 in 1998-99. The lowest number of fruits was found in T3 during 1997-98 and 499.6 fruits in T4 during 1998-99. Control gave better fruiting 470.1 and 638.1 in 1997-98 and 1998-99 than other treatments except T2.
Fruit size (cm)2: Significant difference among various treatments was observed (Table 1, 2). T2 produced the maximum sized fruits. The next best treatment was T4 which was similar to control statistically (27.03 cm2 in 1997-98 and 27.07 cm2 in the next year). T3 was found at the bottom in both the years producing 25.48 and 24.26 cm2 sized fruits in first and second year, respectively.
Average weight of single fruit: T2 maintained its superiority over all other treatments as revealed by Table 1 and 2. It produced a fruit of 186.3 and 193.7 g on average basis during 1997-98 and 1998-99, respectively. The control was found somewhat better than remaining treatments by producing 168.3 and 183.4 g fruits in 1997-98 and 1998-99. Other treatments did not show promising results. T3 and T4 produced one fruit with average weight of 162.5 and 163.2 g in 1997-98 and 187.3 and 181.05 g during 1998-99, respectively.
Total soluble solids: No treatment could affect the amount of total soluble solids and their concentration was noted similar in treated and untreated plants. No statistical difference could be located among them as is depicted in Table 1 and 2.
Juice contents (ml): As a tradition, T2 superseded all other treatments and significant differences were noted in various treatments (Table 1 and 2). T2 gave 105.3 and 111.5 ml juice in both the years respectively. Next position was occupied by control which produced 91.8 and 101.1 ml juice in two consecutive years. T3 and T4 were found statistically similar in both the years and produced juice contents of 89.1 and 92.2 ml in 1997-98 and 99.1 and 96.2 ml during 1998-99, respectively.
Juice percentage: Juice percentage was not affected by any treatment during 1997-98 and all the treatments including control behaved alike (Table 1). However, during 1998-99, a difference in treatment means was noted. Maximum juice percentage was found in T2. The remaining treatments were statistically similar and the juice percentage was 55.3, 53.6 and 49.8% in T1, T3 and T4, respectively.
Discussion
The results of the experiment explained that fertilizers and manures must be applied to citrus in January to have maximum improvement in the production. If the fertilizer is to be applied at other times of the year i.e., April or July, it will not help to enhance the yield, rather than its negative effects may reduce the production. The results of the present studies are according to the findings of Meng et al. (1992), Sharma and Azad (1991) and Ronetz (1993).