In this article we will discuss about the four main practices involved in orchard citrus fruit. The practices are: 1. Irrigation 2. Intercropping 3. Weed Management 4. Manuring and Fertilization.
1. Irrigation:
Water is one of the critical inputs for successful production of citrus fruits. There is a differential response of citrus trees to water requirement during vegetative and reproductive phases. Soil moisture stress is detrimental to plant growth which is linearly related with water use.
The success of citrus cultivation on light and medium textured soils of the Punjab, Haryana and Rajasthan depends largely on irrigation. Generally, kinnow requires more water as compared to sweet orange. The irrigation requirements of lemon, however, are the highest. Grapefruits require more water than oranges but less than lemons. The water requirement of young trees is lower than that of the bearing trees.
The closely spaced trees and those with intercrops require more water because of a greater competition for soil moisture. The use of fertilizers and the spray materials are also known to increase the water requirement of plants. Kinnow trees cannot grow and fruit well in the absence of proper soil moisture. The twig die- back and leaf drop could occur due to water stress. The lower fruit set, excessive fruit drop and reduction in fruit size are associated with unfavourable soil moisture which consequently account for poorer yield.
The weather in north-western India turns increasingly hot and generally dry from March through June. The active growth of plants and fruits of kinnow and other citrus also, taken place during this period. As such, it is a peak period of water use for citrus orchards.
It is suggested that young citrus trees upto 8 years may be profitably irrigated by basin system. The application of irrigation at right time and in right quantity is more important. Under North India weekly irrigation during March to June and fortnightly irrigation during November to February are followed. In Punjab, it is reported that the young plants up to the age of 3-4 years, should be irrigated after 7 days intervals, whereas older trees after 15-20 days interval depending upon climate, rainfall and type of soil.
Utmost care needs to be given to irrigation before sprouting in February, after fruit set in April and in the hot weather, otherwise the growth of the trees may be adversely affected resulting in the excessive shedding of flower/fruits.
In the states of Maharashtra, North Western Region, parts of Tamil Nadu and Andhra Pradesh, plants experience water deficit due to negative balance between precipitation and evaporation. The situation is aggravated by low humidity and high temperature which accentuates evaporative demand. In heavy rainfall areas of North Eastern states, no irrigation is practised.
Mandarin growing in Malnad, Wynad, Palani, Shevaroy and Nilgiri Hills are mostly under rainfed conditions. Moisture stress caused during November to March induces dormancy and is a substitute for low temperature. But the failure of blossom shower and subsequent failure of precipitation demands for irrigation otherwise no flowering or fruit set occurs.
Water requirement of acid lime under tropical conditions of South India was found to be 875 mm per year. Application of 40 litres water per tree was found to be optimum in Dehradun valley. Minimum water need of seedling to save it from permanent wilting was found to be 2.25 litres per plant which could maintain turgidity. It is a practice to supply 60-90 litres water per tree at 7-10 days interval depending upon season in well grown orchards of mandarin and sweet orange under Maharashtra conditions. Maximum water use efficiency in Kinnow, when irrigated was provided at 100-135 cumulative pan evaporation (CPE). Vegetative growth and the second stage of fruit growth are most sensitive to soil moisture conditions. The average weight and juice content has positive correlation with water while sugar and acidity has negative correlation.
Citrus trees are highly sensitive to excess moisture and water-logging conditions. The trees require good soil aeration. The excessive irrigation may result in poor soil aeration leading to reduced growth and yield, predisposing the trees to root rot and other diseases. Excessive irrigation also results in the leaching of essential nutrients from soil as well as in accumulation of certain undesirable salts if the irrigation water is not of good quality.
Citrus trees are sensitive to salinity and the total soluble salts in the irrigation water should not exceed 1000 ppm. Over-irrigation of citrus causes decline of orchards in most cases. Water-logging, particularly near the tree trunk can be avoided by providing mounds of earth around the tree trunk well below the bud union.
Drip Irrigation in Kinnow:
The drip irrigation system in kinnow enables efficient and judicious use of water along with improvement in yield.
2. Intercropping:
In order to utilize the vacant land to generate income till the plants become productive, intercropping is recommended. However, indiscriminate use of exhaustive intercrops may lead to decline of orchards.
Intercropping should not be done in the bearing orchard. But in young and non-bearing orchards, intercropping upto 4 years with a leguminous crop such as guara, moong, mash, cowpea, gram and pea may be done. Guara-wheat rotation with guara as a green manure can be taken in sweet oranges for 5-6 years. Sufficient space should, however, be left unsown to permit young trees to make unrestricted growth.
More of fertilizers should be added to meet the requirements of the intercrop. The fruit tree and intercrops should be provided with independent irrigation system. Tall and exhaustive crops like cotton, chari, bajra, maize, berseem, bhindi and creeper types vegetables should not be grown in the orchards.
During summer season, vegetables like round melon, pumpkin, onions and bittergaurd and leguminous crops like moong, mash, moth and cowpeas may be grown. Guara may be grown as fodder or as green manure crop. Chillies should not be grown in a citrus orchard as they have proved to be harmful to the citrus plants. During winter season, turnip cauliflower, carrot and radish can be grown. Peas and gram make excellent intercrops as they enrich the orchard soil. Senji may be grown as fodder or as a green manure crop.
In Darjeeling, cabbage and peas were found beneficial in mandarin orchards from the cost- benefit analysis. Under Coorg conditions, mixed cropping with Robusta coffee was more remunerative than monoculture, though plant vigour of Coorg mandarin was comparatively suppressed. The best arrangement was Coorg mandarin altered with six rows of Robusta coffee.
Berseem proves to be harmful to citrus trees because it requires frequent irrigation while the citrus trees do not require the same amount of water during winter. Therefore, Barseem is incompatible in irrigation requirements with citrus.
3. Weed Management:
The citrus orchards are infested with monocot and dicot weeds which compete with the main crop for winter, nutrients and space. Besides harbouring the insect pests, the weed roots also secrete toxins which adversely affect growth and fruit bearing.
Cultivation has been the major method of weed control in citrus orchards but it has many drawbacks as it damages feeder roots. Frequent tillage destroys the structure of the surface soil, thus lowering the water holding capacity and permeability of the soil. The weeds like Cynodon dactylon and Cyprus rotundus are difficult to eradicate by light digging or other cultural practices. Moreover, hand weeding is expensive and laborious. Weed management has become an expensive aspect in the cultivation of citrus crops. The cost of cultivation can be considerably reduced by adopting chemical weed control in place of conventional hand weeding.
4. Manuring and Fertilization:
One of the major causes of citrus decline in India is improper and inadequate nutrition. In Punjab, the deterioration and unthrifty growth of citrus trees is reported to be due to lack of adequate nutrition. Citrus trees require a judicious supply of plant nutrients for proper growth and regular harvest of high quality fruits. The ill-fertilized trees may have hidden hunger and in acute cases may show a variety of deficiency symptoms. Fertilizer recommendations have been made based both on experience and experimental results to achieve optimum orchard performance.
For proper growth and development of citrus, about 17 elements have been known to have important role to play. Apart from major nutrients like N, P, K, Ca, Mg, and S, citrus requires micronutrients like Zn, Cu, Mn, Fe, B, Mo, etc. Inadequate nutrition of citrus plants causes serious disorders and may eventually lead to decline of the orchards. Chapman reported that about 18 tonnes of citrus fruits remove about 21 kg nitrogen, 5 kg phosphorus, 41 kg potassium, 19 kg calcium, 3.6 kg magnesium, 2.3 kg sulphur, 40 g boron, 9 g copper, 50 g iron, 13 g manganese and 13 g zinc.