No abstract

Drip irrigation has recently been proposed as a water-saving method for rice cultivation. Growers have observed that rice yields are less under drip irrigation than under flood irrigation; however, the reason is unclear. The objective of this two-factor experiment was to compare the effects of irrigation method (flood irrigation and drip irrigation) and soil temperature (18, 24, and 30°C) on rice physiology and yield. The results showed that at 30°C soil temperature, drip irrigation reduced the photosynthetic activity of rice compared with flood irrigation. Drip irrigation also (i) increased the activities of superoxide dismutase by 5% and catalase by 27% and (ii) reduced endogenous hormone concentrations. At 18°C soil temperature, drip irrigation significantly increased SOD (+ 7%) and CAT (+ 23%) and significantly reduced GA (− 25%) and IAA (− 16%) concentrations compared with flood irrigation. The ZR+Z concentrations were 13% less in drip irrigation than in flood irrigation at low soil temperature. The negative effects of low soil temperature (18 and 24°C) were greater under drip irrigation than under flood irrigation, suggesting that low soil temperature exacerbated the stress that rice was under in the drip irrigation system. Drip irrigation significantly reduced the secondary spikelet number compared with flood irrigation. This led to a significant yield reduction. Overall, the combination of low soil temperature and drought stress may be the main reason for the marked decline in the yield of drip-irrigated rice in northern Xinjiang Province.

Drip-irrigated rice (Oryza sativa L.) is susceptible to iron (Fe) deficiency. The major possible cause of Fe deficiency is the changes in the water regime, which mainly affects the redox potential (E_h) of the soil dictating the solubility of Fe. However, how high soil E_h affects soil available Fe and rice Fe uptake is unclear. In this paper, we investigated the effect of soil E_h on rice Fe uptake under different water management strategies (drip irrigation (DI), flood irrigation (FI) and forced aeration of soil in flooding irrigation (FIO)). The results showed that the diethylenetriaminepentaacetic acid (DTPA)-extractable Fe and Fe^(II) concentration in the soil, Fe concentration and chlorophyll contents of leaves and biomass of rice in FIO were greater than those in DI but significantly less than those in FI. The Fe uptake of the plant in DI was the lowest, but which in FI was the highest. Overall, FIO resulted in a significant reduction in Fe uptake of rice, but greater than that in DI. We concluded that both the decreased soil water content and the increased soil E_h were important factors that caused Fe deficiency of drip-irrigated rice.

Drip irrigation can produce high rice yields with significant water savings; therefore, it is widely used in arid area water-scarce northern China. However, high-frequency irrigation of drip irrigation with low temperature well water leads to low root zone temperature and significantly reduce the rice yield compared to normal temperature water irrigated rice, for example, reservoir water. The main purpose of this paper is to investigate the effects of low soil temperature on the yield reduction of drip irrigated rice in the spike differentiation stage. The experiment set the soil temperatures at 18°C, 24°C and 30°C under two irrigation methods (flood and drip irrigation), respectively. The results showed that, at the 30°C soil temperature, drip irrigation increased total root length by 53% but reduced root water conductivity by 9% compared with flood irrigation. Drip irrigation also increased leaf abscisic acid and proline concentrations by 13% and 5%, respectively. These results indicated that drip irrigated rice was under mild water stress. In the 18°C soil temperature, drip irrigation reduced hydraulic conductivity by 58%, leaf water potential by 40% and leaf net photosynthesis by 25% compared with flood irrigation. The starch concentration in male gametes was also 30% less in the drip irrigation treatment than in the flood irrigation treatment at soil temperature 18°C. Therefore, the main reason for the yield reduction of drip irrigated rice was that the low temperature aggravates the physiological drought of rice and leads to the decrease of starch content in male gametes and low pollination fertilization rate. Low temperature aggravates physiological water deficit in drip irrigated rice and leads to lower starch content in male gametes and low pollination fertilization rate, which is the main reason for the reduced yield of drip irrigated rice. Overall, the results indicated that the low soil temperatures aggravated the water stress that rice was under in the drip irrigated environment, causing declines both in the starch content of male gametes and in pollination rate. Low temperature will ultimately affect the rice yield under drip irrigation.

No abstract