China: Potato evapotranspiration and yield under different drip irrigation regimes

China: Potato evapotranspiration and yield under different drip irrigation regimes

A summary of a paper published in Irrigation Science 23: 133-143, 2004
Courtesy of Netafim University

Kang, Y., Wang, F., Liu, H. & Yuan, B.
Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing

Potato (Solanum tuberosum L.) is relatively sensitive to water stress, which in hot climates usually requires large water application for optimum production. It comprises a major food crop in most countries. In China, potato is grown mainly in the north. The total area for this crop was 4.72 million hectares in the year 2000. The objectives of the present study were: 1) to determine soil water distribution under drip irrigation for treatments of different irrigation frequencies and soil matric potentials thresholds as measured by tensiometers; 2) to examine the effect of the treatments on potato evapotranspiration (ET), yield and water use efficiency (WUE).

The study was conducted at the Luancheng Agro-ecosystems Station of the Chinese Academy of Sciences in Hebei Province. The mean annual precipitation is about 480 mm, falling mainly from July to September. Spring and early summer are normally dry. There were five treatments of irrigation at different soil water potential thresholds measured at 0.2 m depth under the drip emitter (from -15, to -55 kPa), and six treatments of different irrigation frequencies (from once a day to once every eight days). The amount of irrigation water for -15 kPa was based on evapotranspiration during the previous day as measured by lysimeter and for the other treatments the cumulative ET according to the number of days elapsed between irrigations. Drip irrigation laterals were placed in the center of raised beds along the potato plant raw. The potato variety Favorita was seeded on March 8 and harvested on June 17. NPK fertilizer (105,180,130 kg/ha, respectively) was applied at the time of plowing. Soil water potential was measured with mercury tensiometers placed at different depths in each treatment. The total ET for the entire period was estimated by the water balance method.

The daily water application varied during the season from 3 to 6 mm and the total amount of water applied for the SMP threshold treatments were: 153, 132, 111, 89, and 45 mm from -15 to -55 kPa, respectively. The cumulative seasonal amount of applied water for the frequency treatments was 142 mm. The total rainfall for the season was 104 mm. There was no drainage water from any of the treatments. The average soil matric potential (SMP) increased as irrigation frequency increased. As the target value of the SMP increased the average SMP over the whole root zone increased and conversely as the target SMP decreased the size of the dry zone under the emitters increased. Although the amount of water applied to the various frequency treatments was the same (246 mm irrigation plus rainfall) there was a difference in the ET of the treatments, increasing from every eight days to daily irrigation and resulting in improved soil moisture condition. ET decreased also with decreasing threshold SMP.

ET was a linear function of threshold SMP, increasing at a rate of approximately 2.2 mm/kPa from a value of -55 kPa up to a threshold value of -25 kPa above which ET did not change.

Yield was a linear function of the threshold SMP, decreasing at a rate of 258 kg/kPa from a value of 26.7 t/ha at SMP of -25 kPa to a value of 19 t/ha at SMP of -55 kPa. At -15 kPa yield decrease again to a value of 22.6 ton. This decrease may have been due to over irrigation and the concomitant poor aeration. Yield was also a function of irrigation frequency, decreasing from a value of 28.2 t/ha for daily irrigation to 20 t/ha for frequency of eight days. WUE decreased from 127.8 to 118.7 kg/ha-mm as threshold SMP decreased from -25 to -55 kPa, and from 131.6 to 104.1 kg/ha-mm as irrigation frequency decreased from one to eight days.

Results show that drip irrigation is suitable for the irrigation of potato in the North China Plain. Soil matrix potential measured 0.2 m under drip emitter may be used as an indicator for irrigation timing. Based on the results of potato yield, evapotranspiration (ET), and water use efficiency (WUE), a potential threshold value before irrigation of -25 kPa and daily irrigation is recommended for potato irrigation scheduling in the North China Plain.

Key words: evapotranspiration (ET), irrigation frequency, potato, potato yield, root zone, soil matric potential, soil water distribution, water stress, water use efficiency (WUE), yield

Geographic terms: China, Hebei Province