Soil Matric Potential Threshold Research Articles

Simulation of Mulch and No-Mulch Conditions for Various Soil Matric Potential Thresholds for Drip-Fertigated Guava ( Psidium guajava L.) in the Semiarid Region of Northwest India

AbstractField experiments were conducted in a semiarid region of Punjab state, northwest India, for 2 years to evaluate an efficient irrigation schedule for guava under mulch and no-mulch conditions. The experiment involved the effect of mulching and three irrigation threshold values [I1 (−20 kPa); I2 (−40 kPa); and I3 (−60 kPa)] on guava plants under drip irrigation and fertigation. Soil matric potential, irrigation amount, soil water content, and fertilizer (N, P, and K) content were measured, and seasonal crop evapotranspiration as well as water and fertilizer use efficiency were computed regularly during the growing period of the crop. The calibrated two dimensional (2D)/three-dimensional (3D) model was used to simulate soil matric potential, and water and fertilizer movement in the soil under guava trees for mulch and no-mulch conditions. Simulated water movement, soil matric potential, and N, P, and K movement statistically matched those measured using the tensiometers, soil water probes, and soi...

Influence of mulches on urban vegetation construction in coastal saline land under drip irrigation in North China

In order to generate information for reclaiming coastal saline sandy-loam soil for urban vegetation construction around Bohai Bay in North China, a field experiment combined with drip irrigation and setting a gravel–sand layer beneath the saline soil but above the water table was conducted to study the effect of mulches on irrigated water amount, soil salt control and willow (Salix babylonica L.) growth, and construction costs were also estimated during 2012 and 2013. The three mulch treatments were control treatment with no mulch (C1), black shading net mulch (C2) and straw mulch (C3). In order to leach salts in the soil profile, irrigation was triggered by the soil matric potential threshold at 20-cm soil depth of −5kPa in the early stage, and this was changed to −10kPa until the end of the first growing year, and to −20kPa for the second year. The results showed that (1) the straw mulch consumed the least irrigation water, followed by the black shading net mulch and the control treatment. Compared to the control treatment, the amount of irrigation for the straw mulch had decreased by 12% in 2012 and 27% in 2013. (2) The salinity reduction was mainly related to rainfall and the strategy of drip irrigation; and the mulches, especially straw mulch, decreased the risk of salt accumulation in early spring. (3) The best growth characteristic of plants and the optimal investment cost were for straw mulch, and the high investment cost in 2012 was due to soil preparation cost and the willows, gravel and sand cost was high and then it had decreased by 90% in 2013. From the combined points of water saving, plant growth and investment cost, the use of straw mulch with drip irrigation could aid in urban vegetation construction on coastal saline land in North China.

Effects of different drip irrigation regimes on saline–sodic soil nutrients and cotton yield in an arid region of Northwest China

A field experiment was conducted on a saline wasteland in Xinjiang, Northwest China, during 2008–2010 to evaluate the nutrient behavior and cotton yield during reclamation, applied by different drip irrigation regimes. The experiment included five treatments in which the soil matric potential (SMP) thresholds at 20cm depth were controlled at −5, −10, −15, −20 and −25kPa. The results indicated that both soil salinity and sodicity declined significantly at 0–40cm depth and greater reductions were achieved at higher SMP thresholds (−5 and −10kPa) than in other treatments. The distributions in soil inorganic nitrogen (N) and available phosphorus (P) and potassium (K) in the soil profile were mainly influenced by the point-source characteristic of drip irrigation, drip irrigation regime and fertilization mode. With the reclamation of both soil chemical and physical properties, there were dramatic increases in soil N, P and K concentration by the end of 2010. The soil nutrient concentrations in N, P and K were all proportional to the SMP thresholds, as higher SMP could result in greater reductions in soil salinity and sodicity. Since crop growth became more vigorous during reclamation, there was also a considerable increase (9.7–31.9%) in soil organic carbon by the end of 2010, and the concentrations were also proportional to SMP thresholds. The highest cotton yield was obtained in S1 (−5kPa) treatment for both 2009 (2.87Mgha−1) and 2010 (3.60Mgha−1). Additionally, the soil C:N ratios were inversely proportional to the SMP thresholds in 2009 and 2010. Considering the soil reclamation efficiency, soil nutrient stocks and cotton yield, SMP thresholds of −5 and −10kPa could be used as effective measures to trigger irrigation in the first 3 years of saline–sodic soil reclamation in Xinjiang, Northwest China.

Effect of soil matric potential on wolfberry (Lycium barbarbum L.) yield, evapotranspiration and water use efficiency under drip irrigation

The experiment was undertaken in order to investigate the effect of soil matric potential (SMP) on wolfberry yield, evapotranspiration (ET), water use efficiency (WUE) and the implications for soil water management under drip irrigation in the Yinchuan Plain arid region of Northwest China. The experiment consisted of five treatments, which maintained SMP at a depth of 0.2 m immediately under a drip emitter releasing water at -10 (S1), -20 (S2), -30 (S3), -40 (S4) and -50 kPa (S5), respectively, after wolfberry had been planted. The results showed that during the growing season, the target SMP value of the five different treatments was maintained within the experimental design range and the irrigation volume and ET declined as the target SMP value decreased. The temporal and spatial soil water content (SWC) changes observed in the soil profile suggested that the S1 and S2 treatments could meet the crop water absorption demand because the soil moisture was over 15 % and soil water was in excess of crop needs. However, the soil water content for S3, S4 and S5 was less than 15 %, which produced visible water stress in the crop. Statistical analysis for the change values in the electrical conductivity of the saturated soil-paste extract (ECe) showed the significant differences between the different SMP treatments in the middle layer (40 – 80 cm) and the plots S2 (-20 kPa) had the better effect of the soil salinity leached. The highest yield was achieved in the S2 plots and the lowest fresh to dry weight ratio was found in the S3 plots, which also produced the highest quality seed. WUE was in the order S3 > S5 > S2 > S4 > S1. Based on a comprehensive analysis that included irrigation volume, ET value, crop yield and WUE, it is recommended that the SMP threshold should be controlled in the range from -20 to -30 kPa, which was the most favorable drip irrigation schedule for increasing yields and irrigation efficiency. The study should provide information that could be used in other regions suffering from drought and water scarcity. Key words: Deep percolation, irrigation volume, soil salinity, soil water content (SWC), vacuum tensiometers.

Assessment of secondary soil salinity prevention and economic benefit under different drip line placement and irrigation regime in northwest China

This study was conducted in order to evaluate the prevention of secondary soil salinity and the economic benefits of different drip line designs and irrigation regimes in northwest China. A three-year experiment (2008–2010) was carried out in the Xinjiang Autonomous Region of China and included five water treatments and two drip line designs. Irrigation was triggered by the soil matric potential (SMP) threshold at 20-cm soil depth, at −10, −20, −30, −40 and −50kPa for single and double lateral irrigation placements after cotton was established. Soil salinity was significantly affected by the irrigation regime and drip line design. The single line design was more efficient at salt leaching and the areas of low electrical conductivity zones in the soil profile existing throughout the growth season were directly proportional to the SMP threshold. Moreover, the critical SMP value (CSV), which is the lowest SMP threshold that can prevent salinization of soil, was significantly related to soil depth and drip line placement. The lowest CSV of −43kPa was obtained under single line design within the 0–40cm soil depth interval. Seed cotton yields were positively correlated with the SMP thresholds and planting years; and the highest yield of 6.41 Mg/ha was achieved under the double lateral design for SMP of −20kPa in 2010. Economic evaluation showed that total investment cost was around 10% lower for single compared to double lateral design, whereas double laterals produced more net income. From the combined point of economic return and soil salinization prevention, a SMP threshold of −20kPa with double line design was found to be most appropriate for scheduling of cotton drip irrigation and agronomic practices in Xinjiang.

Responses of drip irrigated tomato (Solanum lycopersicum L.) yield, quality and water productivity to various soil matric potential thresholds in an arid region of Northwest China

Considering the current water scarcity of Northwest China, aiming at sustainable agricultural development in this region, it is required to identify and apply the most appropriate practices for water-saving, and yield and water productivity improvement. Relative to the tomato crop, a two-year field experiment was conducted in an arid region of Northwest China using drip irrigation and transparent plastic mulch to study the impacts of various soil matric potential thresholds (−10, −20, −30, −40 and −50kPa) on yields, fruit quality and water productivity. A soil water balance was performed to estimate the seasonal actual ET (ETa) for every treatment and to relate it with the volume of water applied and yields achieved. Crop coefficients were determined from the crop density and height; for the non-stressed treatment the values of 0.30, 1.10 and 1.05 were obtained for the initial, mid-season and late season stages, respectively. A linear relationship between seasonal ETa and applied water was obtained. Tomato yields and ETa decreased with decreasing applied water but fruit quality did not: it was best under mild to moderate water stress (−30 to −40kPa). Water productivity based on marketable-quality yields was the greatest when applied irrigation was 90% of the amount of irrigation required for no stress. This condition corresponds to a soil matric potential threshold of −40kPa. However, a smaller stress may be desired in terms of irrigation management and a threshold of −30kPa is then recommended.

Irrigation scheduling strategies based on soil matric potential on yield and fruit quality of mulched-drip irrigated chili pepper in Northwest China

A two-year field experiment was conducted with drip irrigation and plastic mulch to investigate an appropriate irrigation management strategy for chili pepper (Capsicum annuum L.). Five treatments, with the soil matric potential (SMP) threshold range of −10 to −50kPa at intervals of 10kPa, were applied in this study and are correspondingly referred to as T1 to T5. Leaf area index, plant height, soil water content, yield, and total soluble solids (TSS) were measured, and seasonal crop evapotranspiration (ET), water productivity (WP), and irrigation water productivity (IWP) were computed regularly. Results showed that the differences in leaf area index, plant height, above-ground biomass, and crop yield in treatments T1 though T4 were similar (P>0.05), but higher (P<0.05) than those of treatment T5. Irrigation amount and crop ET generally decreased with decreasing SMP threshold. Threshold values with SMPs from −10kPa to −30kPa caused a reduction of irrigation amount by 22–43% and crop ET reduction by 11–25%. Higher TSS, larger percentage of marketable fruits, and higher WP and IWP were found for treatments T3 and T4 in both growing seasons. The highest SMP threshold (−10kPa) and lowest SMP threshold (−50kPa) greatly reduced the WP and IWP. Therefore, a SMP threshold range of −30kPa to −40kPa at 20cm depth was recommended for irrigation management of chili pepper under mulched-drip irrigation conditions in the arid region of Northwest China.

Growth and yield of oleic sunflower (Helianthus annuus L.) under drip irrigation in very strongly saline soils

A four-year trial was set up to test the feasibility of growing oleic sunflower in a very strongly saline wasteland with drip irrigation in the Ningxia plain of Northwest China. The soil salinity expressed as electrical conductivity of the saturation paste extract (EC e ) was around 28 dS/m, and soil nutrient was deficient in the upper 120 cm depth. The experiment included five soil matric potential (SMP) treatments, with the SMP at 20-cm depth immediately under the emitters maintained to be higher than −5, −10, −15, −20 and −25 kPa after sunflower establishment. Drip irrigation consistently created a favourable soil moisture and low-salinity region in the root zone when the SMP was maintained higher than −25 kPa. The sunflower dry seed yield decreased by 3.8 % for each unit increase in seasonal average soil salinity in the root zone. Plant vegetative growth, yield characteristics, irrigation frequency and irrigation amount all increased with the increase in SMP from −25 to −5 kPa, and the highest irrigation water use efficiency was available when the SMP was between −10 and −15 kPa (the amount of applied water was around 750 mm). Leaching of salts by drip irrigation gradually turned the very strongly saline soil into a moderately saline soil. This research suggests that drip irrigation can be successfully used in oleic sunflower cultivation in this highly saline soil and a SMP threshold between −10 and −15 kPa is suggested for irrigation scheduling.

Effects of different water levels on cotton growth and water use through drip irrigation in an arid region with saline ground water of Northwest China

Due to the mismanagement of water and fertilizer application, cotton cultivation in Xinjiang Northwest China is faced with the problems of soil deterioration and groundwater table ascension. This study was conducted to evaluate the effects of different levels of water applied through drip irrigation on cotton yield and water use in an arid region of Northwest China. The experiment included five water treatments in which the soil matric potential (SMP) at a depth of 20cm was controlled higher than −10kPa (S1), −20kPa (S2), −30kPa (S3), −40kPa (S4), and −50kPa (S5) after cotton was established. The results revealed that the highest cotton evapotranspiration (ETc) was achieved under S1 (−10kPa) treatment and the ETc, deep percolation and the ratio of deep percolation with irrigation water all increased with increasing SMP threshold. After three years experiment, no salt accumulation in surface soil layer was found under our irrigation schedule. The highest seed cotton yield was obtained when the SMP threshold was controlled above −30kPa in 2008, and −20kPa in 2009 and 2010. Moreover, the highest yield obtained after 3 years was 42% higher than the average yield achieved by local farmers in the area. Additionally, the water use value (WUE and IWUE) tended to increase as the SMP threshold decreased in 2009 and 2010. Considering the cotton yield and the impact of irrigation on the underground water table, an SMP higher than −20kPa at 20cm can be used as an indicator for cotton drip irrigation scheduling and agronomic practices in this area to help alleviate the dangerous increase in the water table while increasing the cotton seed yield.

Salt distribution and the growth of cotton under different drip irrigation regimes in a saline area

A 3-year experiment was conducted in an extremely dry and saline wasteland to investigate the effects of the drip irrigation on salt distributions and the growth of cotton under different irrigation regimes in Xinjiang, Northwest China. The experiment included five treatments in which the soil matric potential (SMP) at 20 cm depth was controlled at -5, -10, -15, -20, and -25 kPa after cotton was established. The results indicated that a favorable low salinity zone existed in the root zone throughout the growing season when the SMP threshold was controlled below -25 kPa. When the SMP value decreased, the electrical conductivity of the saturation paste extract (EC(e)) in the root zone after the growing season decreased as well. After the 3-year experiment, the seed-cotton yield had reached 84% of the average yield level for non-saline soil in the study region and the emergence rate was 78.1% when the SMP target value was controlled below -5 kPa. The average pH of the soil decreased slightly after 3 years of cultivation. The highest irrigation water use efficiency (IWUE) values were recorded when the SMP was around -20 kPa. After years of reclamation and utilization, the saline soil gradually changed to a moderately saline soil. The SMP of -5 kPa at a depth of 20 cm immediately under a drip emitter can be used as an indicator for cotton drip irrigation scheduling in saline areas in Xinjiang, Northwest China.

Using plant water status to define threshold values for irrigation management of vegetable crops using soil moisture sensors

Thresholds of soil matric potential (SMP) and available soil water content (AWC) required to prevent water limitations between irrigations were determined for bell pepper, melon, and spring and winter tomato grown in Mediterranean-type greenhouses on the south-eastern coast of Spain. Thresholds were identified by measuring the divergence of leaf water potential of un-watered plants from that of well-watered plants. Soil matric potential thresholds were −58 kPa for pepper, −35 kPa for melon, and −38 to −58 kPa for tomato. In general, SMP thresholds were more negative under lower evaporative demand conditions such as during autumn and winter months. Available soil water content thresholds, for a given crop and drying cycle, differed appreciably depending on soil depth and the method used to calculate the values. For the four crops studied, AWC thresholds calculated at 0–40 cm were 13–15% higher than those calculated at 0–20 cm. Each AWC threshold for 0–20 cm depth was 21–29% lower when AWC was based on laboratory rather than field determinations of field capacity and permanent wilting point. For a given method of calculating AWC, AWC threshold values were similar for different crops and drying cycles, suggesting limited sensitivity of the AWC approach. Using the manufacturer's calibration, the capacitance sensor used for SWC measurements overestimated SWC by an average of 36%. An in situ calibration provided generally good agreement with the actual SWC between 0.15 and 0.22 cm 3 cm −3; however, for higher SWC values, the in situ calibration underestimated SWC. The results of this study demonstrated the uncertainty of using recommended fixed AWC threshold values for irrigation management, using SWC sensors, because of issues related to the definition of rooting depth, measurement of FC and PWP, sensor calibration, and sensor accuracy across the relevant range of water contents. These data suggest that SMP thresholds are much more reliable than AWC thresholds for scheduling irrigations in greenhouse-grown vegetable crops. Technical issues regarding on-farm measurement of SMP and SWC are discussed.

Potato evapotranspiration and yield under different drip irrigation regimes

A field experiment comparing different irrigation frequencies and soil matric potential thresholds on potato evapotranspiration (ET), yield (Y) and water-use efficiency (WUE) was carried out in a loam soil. The experiment included five treatments for soil matric potential: F1 (-15 kPa), F2 (-25 kPa), F3 (-35 kPa), F4 (-45 kPa) and F5 (-55 kPa) and six treatments for irrigation frequency: N1 (once every day), N2 (once every 2 days), N3 (once every 3 days), N4 (once every 4 days), N6 (once every 6 days) and N8 (once every 8 days). Results indicate that both soil matric potential and drip irrigation frequency influenced potato ET, Y and WUE. Potato ET increased as irrigation frequency and soil matric potential increased. Comparing soil water potential, the highest ET was 63.4 mm (32.1%) more than the lowest value. Based on irrigation frequency treatments, the highest ET was 36.7 mm (19.2%) more than the lowest value. Potato Y and WUE were also found to increase as irrigation frequency increased. Potato Y increased with an increase in soil water potential then started to decrease. The highest Y and WUE values were achieved with a soil matric potential threshold of -25 kPa and an irrigation frequency of once a day.

Optimization of water for fruit trees by a computerized irrigation system

irrigation according to programmable threshold soil matric potential (SMP) levels. The SMP control determined the water content and the irrigated soil volume and possibly the size of the active root system. This method enabled water to be supplied at the rate of consumptive use of the trees, and should eliminate water and mineral percolation to soil layers below the active root zone. During 3 consecutive years treatments consisting of high and low SMP threshold levels and a common commercial irrigation regime according to pan evaporation coefficients were applied. The control of SMP may stimulate root production in a limited volume of soil and thereby induce physiological root restriction effects such as reduction of vegetative to reproductive growth ratio. The main result obtained was a decrease in vegetative growth without impairing crop load (the ratio of reproductive to vegetative growth - kg fruit/cm2 trunk growth) and fruit size in the low SMP treatment irrigated with 213 mm less water than the treatment according to pan evaporation. It was concluded that this system of irrigation may reduce the size of the trees, and thereby increase light penetration, improve fruit quality, and lower the cost of production. This method will permit the planting of economically successful high density orchards.