The Effects of Water-nitrogen Regulation on Cotton Roots in Drip-irrigated Salinized Soils

Abstract

【Objective】 Root growth and its consequence for water and nutrient uptake from soils are modulated by a multitude of biotic and abiotic factors. The aim of this paper is to study the effect of water-nitrogen coupling on the roots of cotton in drip-irrigated salinized soils. 【Method】 The experiment was conducted in pots packed with mildly salinized soil (4~5 g/kg), with the local cotton variety Nongfeng 133 used as the model plant. All pots were drip-irrigated. There were three nitrogen (urea) fertilizations: 300 (N1), 600 (N2) and 900 kg/hm2 (N3), and three irrigation treatments: 2 750 (W1), 3 750 (W2) and 4 750 m3/hm2 (W3). We measured dry-root weight to compare the difference between the treatments. 【Result】 Irrigation affected the roots more significantly than nitrogen fertilization. When nitrogen fertilization was the same, the dry root weight increased first and then fell with the increase in irrigation amount. Along the soil profile, the dry root weight decreased with the soil depth in the 0~40 cm soil layer, and increased with depth in the vicinity of the pot bottom. Increasing irrigation amount and nitrogen application in certain ranges increased dry root weight in the soil below the depth of 30 cm. Horizontally, reducing irrigation amount led to a reduction in dry root weight in the soil distant from the emitter. Increasing nitrogen application did not promote horizontal root growth. The dry root weight decreased along the soil depth, especially in the 0-30 cm soil layer in which the dry root weight declined with depth steadily. The effect of water- nitrogen coupling on the roots was significant (P<0.01). 【Conclusion】 The effect of nitrogen on the root system was modulated by soil water, and on average increasing nitrogen fertilization negatively affected root growth at significant levels.

Keywords

• salinized soil
• drip irrigation
• cotton
• water-nitrogen coupling
• root dry weight