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A field experiment based on a monolith method using flooding irrigation under mulch film (FI) as a control was conducted to investigate soil salinity dynamics under drip irrigation with mulch film (DI) and its effects on cotton root length. The average soil salinity increased with duration of irrigation, but salt distribution in the soil profile was uneven and showed strong accumulation in the soil between adjacent mulch films. With advancing growth of cotton plants, the area of salt accumulation gradually expanded, especially from 110 to 125 days after sowing (DAS), when salinity distinctly increased in the 0- to 40-cm soil depth and at distances 30–70 cm from drip lines; the electrical conductivity (EC) under DI in all soil samples was at least 3 mS cm−1and in some cases exceeded 5 mS cm−1. Root length declined significantly by 18.1% from 110 to 125 DAS under DI. The soil area showing the greatest decline in root length under DI coincided with the main site of salt accumulation. Correlation analysis of soil EC and root length density indicated the root length declined when soil salt content exceeded 2.8 mS cm−1. However, under FI salt accumulation barely exceeded 2.8 mS cm−1and no reduction in root length was observed. The results indicated that the main reason for decreased root length in cotton under DI was localized accumulation of salinity. [ABSTRACT FROM AUTHOR]

A pot experiment was carried out with the following treatments: non-mycorrhizal control and inoculation by arbuscular mycorrhizal fungi (Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe or Sclerocystis sinuosa Gerd. & Bakshi) at four P levels (0, 9.5, 19, and 38 mg P kg[sup -1]). Cotton (Gossypium arboreum L. cv. Xin-lu-zao No.l) was used as the host plant. The [sup 15]N-labeled urea (2.5% abundance) was mixed with soil thoroughly at a rate of 100mg Nkg[sup -1]. Colonization by the two arbuscular mycorrhizal fungi significantly improved the growth of cotton plants at all P levels compared with non-mycorrhizal plants. Nitrogen concentration in shoots was not significantly affected by arbuscular mycorrhizal fungi, while the nitrogen content was significantly higher in mycorrhizal plants than in non-mycorrhizal plants. The [sup 15]N atom % excess in mycorrhizal plant was significant lower than that in non-mycorrhizal plants. Considering the derivation of the nitrogen in the cotton plants, mycorrhizal fungi had no significant influence on uptake of nitrogen derived from fertilizer, but increased nitrogen derived from soil significantly. Colonization by mycorrhizal fungi increased the amount of soil available nitrogen ("A[sub N]" value). The results indicate that arbuscular mycorrhizal fungi may facilitated plant acquisition of nitrogen from sources which are not or less available to non-mycorrhizal plants. [ABSTRACT FROM AUTHOR]