Tahira Abbas, *Dr. Rashad M. Balal, Dr. Saeed Ahmad, *Dr. M. Afzal and M. Adnan Shahid
Institute of Horticultural Sciences, University of Agriculture 38040 Faisalabad.
*University College of Agriculture, University of Sargodha, Sargodha.
Citrus is a leading fruit crop of Pakistan. The genus Citrus is the member of family Rutaceae in plant kingdom with diversity of species. Kinnow mandarin (C. reticulataBlanco) is the best one amongst other species due to its high yield, fresh consumption, aromatic flavor, high processing quality and better adaptation to agro-environmental conditions of Punjab. It is a rich source of vitamin C, and provides some macro and micro nutrients such as calcium, phosphorus and iron. Citrus fruit prevents liver, lungs and skin cancers, heart diseases, birth defects and contributes to a balanced and healthy life style to humans. Importance of citrus to agriculture and world’s economy is demonstrated by its wide distribution and large-scale production. It is economically potential fruit and is grown in more than fifty two countries of the world. Pakistan is bestowed with suitable climate to grow citrus especially Kinnow mandarin. Citrus occupies an area of 193,000 hectares with annual production of 1472,000 tons (MINFAL, 2006-07).
Sustainability in agriculture is an important goal, which can be gained through the effective and economic utilization of natural resources as well as careful management of agricultural inputs. Fertilizers are the important input, which is proved to be essential for better and quality production. The rising prices, timely availability, adequate doses and purity of fertilizers are the important considerations now days. Deficient and excessive fertilization induces ill-effects on crop health and produce quality. The fertilizer requirements of plants differ with nature and age of plant, edaphic and climatic factors. Balanced nutrients availability at the proper growth stage improves yield, quality and other growth characters. Organic matter (O.M) acts as store house of nutrients and can reduce the use of mineral fertilizers. Organic fertilization enhances vegetative growth, nutritional status and reduces the residual effects of nitrates and nitrites in fruits.Organic matter significantly affects the soil microbial activity, soil aggregation and utilization of chemical fertilizers. Soil organic matter status in orchards can be raised by adopting conventional methods like utilization of farm yard manure (FYM), crop residues, composts and growing cover crops (Green Manuring) etc. The adaptation of these practices by farmers is rare because of unavailability of materials, economic condition of farmers and possible risk of damaging root system of fruit trees while incorporating cover crop etc.
Non conventional sources utilized for improvement of soil organic matter status include use of humate products as bio-fertilizers and bio-stimulants, which should be encouraged among farmers. They prove to be an immediate source of improving soil fertility. It is advantageous over conventional organic matter sources because of easy availability, feasibility in using over large area, immediate response to plants, less handling problems and keeping the environment, pollution free.
Farmers are following a recommended pattern of fertilization in citrus but 3-4 folds low productivity as compared to other countries, indicate the need for further improvement. This improvement can be encountered through the supplementation of various organic bio-stimulants and bio-fertilizers with the recommended fertilization pattern. These bio-stimulants are helpful in enhancing the efficiency of fertilizers by providing suitable environment for effective plant growth. These bio-stimulants beneficially alter the soil conditions and encourage the soil microbial growth.
The reasons which contribute largely for low average yield of the Kinnow mandarin in the country are the improper use of fertilizer and less use of bio-fertilizers. Bio-fertilizers play a vital role in improving the fruit quality as well as production by increasing the nutrient uptake of plants. Due to population pressure in the country, our agricultural products fail to meet the food, feed, fodder and industrial raw material demands. Therefore, it is necessary to utilize suitable available bio-fertilizers to enhance our food quality and quantity. Synthetic fertilizers are very costly and do not fulfill the farmer’s demand, so there is a need to use biochemicals like humic acid and micro nutrients to increase yield with superior quality fruits. Among these bio-stimulants, humic substances are identified as beneficial source for supplying humic acid, fulvic acid and humins. Humic substances are organic in nature with significant distribution in soil, fresh water, sewage, compost, oceans, lignite and brown coals. These are partially decomposed material, originated as a consequence of biological and chemical breakdown of animal and plant life. It estimates the production potential of the soil.
Humic substances (humic and fulvic acid) constitute 65-70 % of the organic matter in soils. Humic acid is one of the major components of humic substances which are dark brown in color. These humic substances represent major constituent of soil organic matter (humus), which contributes to physical and chemical properties of soil. Humic acid is a condensed, complex mixture of aromatic organic acids. It contains sulfur, nitrogen and phosphorous in varying percentage and some metals like Ca, Mg, Cu and Zn etc. It is insoluble in water but alkali soluble which renovate the organic matter status of the soil and enrich it for better crop growth. Humic acid is reported to be more beneficial in soils with less than 2 % organic matter contents.
Humic acid can be used for soil amendment to improve soil quality and health, which ultimately improves fruit quality and production. It biologically stimulates the plant growth, chemically changes the fixation properties of the soil, improves cation exchange capacity and modifies the soil, physically. Addition of humic acid in the soil stimulates enzyme activity, photosynthesis, increases root growth, respiration, maintains the transpiration rate, increases the permeability of plant membranes, promotes uptake of nutrients, increases protein and vitamin contents and yield of dry matter. Humic acid improves the soil physical conditions by making it more friable or crumbly, by increasing soil aeration, by improving soil drainage and soil moisture retention. Chemically, it increases buffering properties, chelates metal ions under alkaline conditions, retains water soluble inorganic fertilizers in the root zones and releases them to plants, when needed. Moreover it promotes the conversion of a number of elements like nitrogen (N), phosphorus (P), iron (Fe+2, Fe+3), copper (Cu), calcium (Ca), magnesium (Mg), lead (Pb) into available forms to plants. Humic acid influences the plant growth depending upon the concentration used and performs as harmone like substance, which enhances the growth. Humic acid is found to affect the morphological, physiological and biochemical attributes of different crops, thus enhancing the yield and fruit quality.
Humic acid positively alter the soil fertility status and reported to reduce the hazardous effects of synthetic fertilizers. It is used as a supplement to chemical fertilizers to enhance their utilization in many crops including watermelon, squashes, potato, grapes, tomato, strawberry, pepper, cucumber, spinach, lemon, grapefruit, apple and guava and citrus. Humic acid complexes with colloidal soil surface, which prevent its leaching and minimize the adverse residual effects of pesticides by immobilization. It removes excessive pesticides from soil, thus helpful in environment protection. It also retards the induction of chlorosis by improving the Mg++and Fe++uptake by plants. It also reduces fertilizer requirement of the crop by encouraging the activity of microorganisms which enhances the plant growth.