Evaluation of humic substances fertigation through surface and subsurface drip irrigation systems on potato grown under Egyptian sandy soil conditions

Abstract

The aim of this study was to evaluate the effect of humic substances application in sandy soil under surface and subsurface drip irrigation systems on potato tubers yield quantity, quality, nutrients concentration in tubers and soil fertility after harvesting. For this purpose, field experiment was carried out at the experimental farm of the Agricultural Research Station, National Research Center, El-Nubaria district, Egypt during the winter season of 2007/2008. The used experimental design was split plot design with three replicates, main treatments were presented irrigation systems, i.e. surface and subsurface drip irrigation, while subtreatments were presented rates of humic substances additives which were 0, 60 and 120 kg ha⁻¹. Results showed that increasing humic substances application rates up to 120 kg ha⁻¹ enhanced tubers yield quantity, starch content and total soluble solids. The increase of humic substances application rates was associated with the decrease of nutrients leaching, which was reflected on increasing macro- and micronutrients concentration in potato tubers, as well as increasing concentration of these nutrients in soil after tubers harvesting. Subsurface drip irrigation system was found to be more efficient than surface drip irrigation system on improving tubers yield quantity, quality parameters and nutrients concentration content, in addition to soil fertility after harvesting.

Introduction

During the past century, Egyptian population has increased more than five times, from 11 million in 1907 to more than 70 million at the beginning of the year 2007, while the area of its cultivated land has changed slightly from 2.3 million hectares to approximately 3.6 million hectares during the same period, and this has led to a shortage in food supplies. Consequently, management of sandy soils through proper reclamation measures to increase crop productivity assumes a great deal of interest in a day wherein the available land area for cultivation is declining all the time.

There are specific problems in the management of sandy soils including their excessive permeability, low water and nutrient holding capacities (Suganya and Sivasamy, 2006). Therefore, managing the use of irrigation water and plant nutrients is a major challenge of sandy soil amelioration efforts.

The term ‘micro-irrigation’ refers to drip, trickle, spray, micro-jets or mini-sprinkler systems designed to use available water more effectively that slowly and frequently provides water directly to the plant root zone. Moreover, drip irrigation provides an efficient method of fertilizer delivery virtually free of cultural constraints that characterize other production systems. Subsurface drip irrigation is considered to be the most modern irrigation system with efficient water delivery that can contribute immensely on improving crop water use efficiency and conserving water (Hanson and May, 2004). Most agricultural irrigation scientists are in agreement that fertilization through subsurface drip irrigation system could be the ideal fertigation systems. Rajkumari et al. (2006) hypothesized that injecting N fertilizer into subsurface irrigation systems should in theory be as efficient as the irrigation delivery system itself is.

Achieving maximum fertigation efficiency requires knowledge of crop nutrient requirements, soil nutrient supply, fertilizer injection technology, irrigation scheduling, crop and soil monitoring techniques. If properly managed, fertigation through drip irrigation lines can reduce overall fertilizer application rates and minimize adverse environmental impact of vegetable production (Hochmuth, 1992).

Humic substances are the final component of organic matter decomposition, and its benefits in agricultural system are its ability to capture more moisture content, which will increase water use efficiency in the amended sandy soil when compared with the unamended one. This could be due to the phenomenon of swelling and retention of water by the amended soil (Suganya and Sivasamy, 2006). Otherwise, humic substances are able to complex metal ions (Stevenson, 1982) which will decrease nutrients leaching with irrigation water, and increase fertilizers use efficiency. Humic substances are relatively stable products of organic matter (Mackowiak et al., 2001); accumulate in the environmental systems to increase moisture retention and nutrient supply potentials of sandy soils (Suganya and Sivasamy, 2006).

Intense competition for reduced international supplies of cereals and other agricultural commodities is driving worldwide food price inflation, which brings with it the risk of food shortages and social unrest in low-income countries. One strategy that could help to reduce this risk is the diversification of food production to nutritious and versatile staple crops that are less susceptible to the vagaries of international markets, and the best one of such crops is potato.

Potato (Solanum tuberosum L.) is a major food crop in many countries, it rates the fourth ranking among the world's various agricultural products in production volume, and it comes after wheat, rice and corn (Fabeiro et al., 2001). Potato is relatively sensitive to water stress that yield reductions and loss in tuber grade, which makes the availability of soil water one of the most important factors affecting the yield and quality of potato (El-Ghamry and El-Shikha, 2004).

The main aim of our study is to examine the extent to which humic substances additives could be effective in improving potato tubers yield, tubers quality parameters and its nutrients concentration as well as nutrients remained in soil after harvesting stage under both surface and subsurface drip irrigation systems in sandy soil to be included in the fertigation systems.