Effects of irrigation threshold and lateral depth on tomato growth in greenhouse

Soil water is critical for crop growth, yield and water use efficiency. In order to study mutual responsive mechanism between root growth and different irrigation methods (e.g., deficit and lateral irrigation) on soil water distribution, root distribution and dry matter distribution in tomato, a test of subsurface drip irrigation was conducted in a sunlit greenhouse in Dazhai Villiage, Dazhai Town, Yangling City, Shaanxi Province. The study was designed as a 2-factor experiment-lateral depth (D) and irrigation threshold (I). The lateral depth was divided into 4 levels (0 cm, 10 cm, 20 cm and 30 cm) below the surface of ridges and the irrigation threshold set at 50%, 60% and 75% of field capacity. Each treatment was repeated 3 times. The results showed that lateral depth had a significant effect on water consumption of tomato under mild water deficit (75% of field capacity) and moderate-mild water deficit (60% of field capacity) conditions, while lateral depth of 10-20 cm was much better for root water uptake than other treatments. Increase in lateral depth reduced the distribution of roots in the 0-20 cm soil layer, but promoted the growth of roots in the 20-60 cm soil layer. Lateral depth had a significant effect on root growth in the 0-10 cm, 20-30 cm and 30-40 cm soil layers, but had no significant effect on root growth in the 50-60 cm soil layer. Root length and root surface area of fine roots (with diameter less than 1 mm) and coarse roots (diameter greater than 1 mm) of tomato were significantly affected by irrigation threshold. However, lateral depth only had a significantly effect on root length and root surface area of fine roots. Then mild water deficit and lateral depth of 20 cm favored root length and surface area growth of fine roots, but reduced the growth of coarse roots. Mild water deficit and lateral depth of 20 cm better favored total dry matter accumulation, while the 75% of field capacity treatment increased root dry matter allocation. Then lateral depth of 20 cm promoted dry matter accumulation of stems and leaves, but reduced the distribution ratio of root dry matter. For the observed responses, information on how root distribution and dry matter allocation in tomato adapted to different irrigation methods provided a useful guide for field production practices and possible indicator mechanisms for high quality/yield.