Author
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Alva, Ashok |
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Submitted to: Proceedings of the International Fertigation Symposium
Publication Type: Proceedings Publication Acceptance Date: 7/1/2005 Publication Date: N/A Citation: N/A Interpretive Summary: Improvements in fertilizer delivery techniques are sought for two reasons: (i) application of fertilizer in small doses spread across the entire growing season in an effort to match the crop nutrient requirements, to improve nutrient uptake efficency, minimize losses, thus to maximize the returns per unit amount of fertilizer; and (ii) minimize nutrient leaching below the rootzone, particularly of nitrate form of nitrogen, which can have negative impact on raising its concentration in the groundwater above the maximum contaminant limit that is recommended for drinking water quality. In the case of large spacing planted tree crops, drip or under-the-tree micropsprinklers (microirrigation) provide an opportunity to irrigate a certain portion of the total planted area, thus contribute to increased water uptake efficiency. Application of fertilizers through irrigation system is referred to an 'fertigation'. Fertigation through microirrigation system provides a technique of application of water and nutrients to an area of the soil where most of the roots are present to coincide with the timing of nutrient requirement by the trees. Therefore, fertigation is expected to increase the nutrient uptake efficency, thereby minimizing leaching losses compared with the application of fertilizer in dry granular form broadcast over a large soil area at less frequent intervals. In this paper, the recent long-term experimental data on citrus to compare the fertigation and dry granular broadcast methods are summarized. In addition to the tree response, fruit yield and quality, the changes in groundwater nitrate concentrations impacted by the different fertilizer delivery methods are discussed. Technical Abstract: Advances in micro irrigation techniques, i.e. drip and under the tree sprinklers, have facilitated greater adaptation of fertigation especially for perennial crops including citrus. It is generally believed that fertigation improves nutrient uptake efficiency, thereby it is preferable to the dry fertilizer broadcast application by increasing the yield as well as crop quality and minimizing loss of nutrients, i.e. leaching of NO3-N below the root zone. The evaluation of tree response to changes in nutrient management requires long term studies because of large nutrient reserve in the woody portion of the tree. In this paper we have summarized the recent studies on evaluation of fertigation for citrus. Two year studies on newly planted citrus trees showed no significant difference between the fertigation and dry fertilizer broadcast treatments. This is in part due to very low nutrient demand during at least two years after planting. Conditioning the trees with different nutrient management programs since the planting and evaluation done during the seven and eight-year old trees showed significantly greater fruit yield as well as total soluble solids yield with fertigation as compared to those with dry granular fertilizer broadcast application. The optimum N rate with continuous fertigation treatment was lower by 35kg.ha-1 as compared with that for the dry fertilizer broadcast treatment. Six year study on twenty-plus year old ‘Hamlin’ orange trees on ‘Cleopatra mandarin’ rootstock showed no significant difference between the fertigation and dry fertilizer broadcast treatments. A five-year study on thirty-five plus year old ‘Valencia’ orange trees on ‘Rough Lemon’ rootstock showed a significant decrease in surficial aquifer NO3-N concentration under the trees which received total fertigation as compared to that of the trees which received dry granular broadcast (3 appl/year) of similar N rates. In the former, the groundwater NO3-N concentrations were below the maximum contaminant limit (MCL) of 10 mg/L while those of the latter were above the NO3-N MCL throughout the duration of the study. |
