Fertilizer Effects on Soil Moisture Changes during Crop Growing Seasons of Dryland Agriculture in Northwestern Alberta, Canada

Efficient use of limited soil moisture resources is important for crop production in dryland agriculture in the study area. Understanding the changes in soil moisture during crop growing seasons can improve crop production. The objectives of the current study were to assess the effects of fertilizer application on soil moisture content (SMC) and its depletion patterns during the growing season. Changes in SMC in the 0-10, 10-20, 20-30, and 30-40 cm depths soil were monitored during the 2013-2015 growing seasons under canola (Brassica napus L.) and barley (Hordeum vulgare L.) crops with 0 and 100% rates of commercial chemical fertilizers. The crops were grown using direct seeding (DS) on a clay loam soil in the southeast Peace Region (legal: NW7-77-20W5; GPS: 5539′38.43′′ N, 1176′10.64′′ W) of Alberta, Canada. Fertilizer application reduced the SMC at all the soil depths during considerable crop growing seasons. Depletion of SMC started earlier in fertilized pots in 2013 and 2014, but not in the drier early season of 2015. Rapid depletion during the early and middle of growing seasons was followed by slower or no soil moisture depletion by crops near the end. The SMC tended to be somewhat lower under 100 than 0% fertilizer by the end of the growing seasons, with few exceptions. The start of SMC depletion and appearance of fertilizer rates effect after seeding was also influenced by the amount of SMC at seeding in spring, i.e. earlier in dry year of 2015 than in other years with higher SMC in spring and more rain. The results demonstrated that applying fertilizer increased soil water use by plants regardless of the crop type or growing season. They also indicated that if more soil moisture was available, the differences between fertilizer treatments might have continued for extended periods, and yields of fertilized crops may have benefitted more.


Introduction
The water used by dryland crops produced in the study area comes from rain during the growing season, the stored SMC from rain/snow before seeding, and water depleted from the root zone (stored soil moisture: at seeding-at harvest of the crops). The temporal and spatial changes in the soil moisture during the growing season depend on the amount of rain during the growing season and SMC depletion by crops from different depths in the soil profile. In such areas, rainfall, water shortage, low nutrient availability, and low water-use efficiency (WUE) are the main factors limiting crop growth (Zhang et al., 1998;Li et al., 2001). Wallace (2000) emphasized the need to increase WUE by more effectively using water resources for plant production to meet the challenge for us and future generations to provide a stable and secure food supply and the efficient use of our natural resources of soil, water, and air. The increasing variability in both temperature and precipitation throughout the world raises the question of how to enhance WUE under current cropping systems, and climate change increases the urgency for optimizing the factors to enhance the stability of crop production across a range of climates (Hatfield, 2011). 10 P, 41 N + 20 P, and 64 N + 25 P, kg ha -1 ) than no fertilize at the tillering, stem elongation, booting, grain filling, and harvesting stages of tef (Eragrostis tef (Zucc)) crop. The results from the above studies imply that when fertilizer rate increases, there is increased soil water depletion by the plants because more nutrients are available regardless of crop type or variety (Caviglia & Sadras, 2001;Huang et al., 2003;Zhang et al., 2006;Zou et al., 2012;. Ritchie and Johnson (1990) stated that fertilization significantly influenced soil water content because fertilization stimulates plant growth, affecting plants' use of soil water and its distribution. Other reports have shown that adequate nutrient supply can contribute to increased water and nutrient uptake (more water used) by plants from the soil for producing better crop growth (Salvagiotti et al., 2008, Setiyono et al., 2010. Reports have also stated that long-term N and P fertilization considerably increased crop water use for transpiration, decreasing soil moisture in a soil profile (Caviglia & Sadras, 2001;Huang et al., 2003;Zhang et al., 2006;. Nielsen and Halvorson (1991) stated that generally plant height, above-ground biomass, leaf area index, rooting depth, water use, and grain yield increased with increasing N rate. However, increasing N rate increased rooting volume and lowered water stress under adequate water supply, but increased water stress when the excessive transpiration demand of the resulting larger leaf area and vegetative mass was not fully compensated by the increased rooting volume. They found the corn (Zea mays L.) grain yield was linearly correlated with increased cumulative evapotranspiration from N application, but increasing levels of N fertility was detrimental to winter wheat (Triticum aestivum L.) yields when water-limiting conditions reduced evapotranspiration rates to less than 62% of potential evapotranspiration. Wallace (2000) concluded the challenge for us and future generations would be to provide a stable and secure food supply and the efficient use of our natural resources, soil, water, and air.
Plant's ability to obtain water and nutrients from the soil has been related to their capacity to develop their root systems. Greater length, surface area, and volume of canola and barley roots with 100 than 0% fertilizer were reported during the early growing season of 2015 under both the minimum tillage and direct seeding systems (Gill, 2021). Gan et al. (2011) suggested that a crop's root system can compensate by increasing or relocating maximal root growth to higher soil moisture regions, thus helping maintain plant growth under dry soil conditions (Rendig & Taylor, 1989). The root length density of crops during the dry season tended to decrease mid-season at shallow soil depths, whereas it continued to increase throughout the growing season at deeper soil depths (Moroke et al., 2005). These changes were parallel to the maximum soil moisture depletion trend from successively deeper layers as the season progressed.
Farmyard manure combined with inorganic fertilizers was shown to play important roles in better water penetration (Hati et al., 2006), and firm and deep establishment of crop roots . Fertilizers and manure helped plants extract water from deeper soil layers and maintain high relative plant water content under soil moisture stress conditions in rain-fed farming (Hati et al., 2006). Such integration is regarded as a fundamental approach to improving efficient water use in crop production (Mohanty et al., 2007).  stated that manure application or increasing the fertilizer application rate could reduce soil water evaporation, make reasonable use of soil water and improve water-use efficiency at different growth stages of maize. Campbell et al. (1988) observed that the yield increase of spring wheat per unit of moisture use during 1967-1984 tended to be greater for the better-fertilized rotations and that precipitation during the grain-filling period was most important. Increased barley, canola, and wheat yields were observed with fertilizer applications during the 2010-2015 (Gill, 2019).
The preceding literature review demonstrated the effects of additional nutrients on the soil moisture changes and crop growth under several climatic, agronomic, and soil conditions. However, there has been limited research on the effects of fertilizer on SMC and its depletion patterns during the growing seasons under rainfed agriculture conditions prevailing in the study area. We hypothesized that SMC and its depletion pattern during the growing season and residual SMC would be affected by fertilizer rates. Thus, changes in SMC and its depletion pattern were monitored during three growing seasons of canola (Brassica napus L.) and barley (Hordeum vulgare L.) that received 0 and 100% fertilizer rates.
More details on the treatments and experimental layout are available in Gill (2019). Briefly, the four fertilizer rates (0, 60, 100, and 140% of the soil tests-based recommendations) were replicated four times in two adjoining areas (canola and cereal sites) from 2010-2015 (6 years), under DS (direct seeding) and MT (minimum tillage) systems. A canola-cereal rotation (most commonly used by farmers in the area) was used on both sites.
For the present study, the soil moisture data were collected during 2013, 2014, and 2015 from the canola and barley plots that had received 0 and 100% fertilizer rates under the DS system. Soil test-based N, P, K, and S amounts were applied in the 100% fertilizer rate plots (Table 1). Fertilizers were applied at seeding, using combinations of seed row placed 11-52-0, and banded away from seed row 46-0-0, 0-0-60, and 20.5-0-0-24 commercial fertilizers.  ; 14, 2013, 6, 2014, and 28, 2015. Spring soil moisture (SSM) and monthly precipitation during the growing season data were obtained from the weather station at Ballater in Alberta, located 5 km from the site ( Table 2). Soil moisture was measured from the depths of 0-10, 10-20, 20-30, and 30-40 cm, designated as 5, 15, 25, and 35 cm depths for presentation, respectively. The frequency of measuring the SMC was decided considering that plots were not too wet and occurrence of rainy and dry periods during the growing season of crops. A profile probe (PR2-UM-3.0) and a moisture meter (HH2 version 4.0) of the Delta T Devices Ltd, 2008, 130 Low Road, Burwell, Cambridge, CB25 0EJ (www.delta-t.co.uk) were used to measure soil moisture. The profile probe has a sealed polycarbonate rod (~2.5 cm diameter) with paired stainless steel electronic sensors at fixed intervals along its length. When power is applied, each pair of sensors generates a simple analog DC voltage (100MHz) that transmits an electromagnetic field extending about 10 cm in the soil. The moisture meter was used to apply power to the profile probe sensors, measure the output signal voltage returned, and convert it to soil moisture units (volumetric) using a linearization table and soil-specific parameters. The signal's strength is related to the permittivity of soil, predominantly dependent on its water content (permittivities: ≈ 81 for water, ≈ 4 for soil, and ≈ 1 for air, Farad m -1 ). Specified fiberglass access tubes (2.5 cm diameter) were installed at the start of each growing season to insert the profile probe for readings at different soil depths.
The soil moisture data for the 0 and 100% fertilizer rates are presented in Figures 1-6, with their standard deviations indicated by vertical lines. The differences between the soil moisture data for the 0 and 100% fertilizer rates at different soil depths (5, 15, 25, and 35 cm) were compared using the Paired sample t-test for each soil depth. The standard error (SE) values and significance of the level of differences from the Paired sample t-t between th  The SMC at all four depths did not show any change until 44 DAS (Figures 1a and 1b), apparently due to very little water use during the crop-emergence and early growth periods and adequate rain received to cover the water use by the crop under both fertilizer rates (  Vol. 14, No. 3;2022 The SMC at all four depths increased or did not show any change until six (6) DAS due to rain and very little water use during the crop's emergence period (

2014 Season
The growing season started with 81% of the normal SSM but had only 47% of normal rain during the growing season with lower than the average amounts received each month (Table 2).

Canola
The SMC at 5 cm depth increased until 23 DAS due to rain ( Figure 3a, umn, soil the moisture content of the soil, but with rare exceptions, soil moisture depletion occurs during the growing season. Crop yields suffer in years with less than normal rainfall, especially when SMC is low at the start of the growing season. Soil moisture depletion occurred under both crops at the 5, 15, 25, and 35 cm depths during 2013, 204, and 2015, which was expected under the dryland conditions prevailing in the study area (Figures 1 to 6). The changes in SMC during and at the end of crop growing seasons, provide information on how fertilizer addition can influence the extent and timing of soil moisture depletion.
During much of the three growing seasons of both crops, SMC at the monitored soil depths was lower with 100 than 0% fertilizer (Figures 1 to 6). However, the duration of these periods of differences between the two fertilizer treatments varied without any consistent trend for the year, crop, or soil depth. For canola, this period lasted for 39-70, 29-86, 49-56, and 49-70  Two reasons were considered responsible for no consistent trend in the duration when SMC was less in 100 than 0% fertilizer. One, there was an almost equal amount of soil water under both fertilizer treatments at seeding time (Figures 1 to 6). Second, there is a progressive reduction in the ability of plants to use water as the soil moisture level decreases because water gets held more tightly by soil particles. So with more water being extracted by plants in 100% fertilizer treatment from the amount present at seeding, it became more challenging for the plants to extract more water when the SMC fell below a certain level. Thus the 0% fertilizer could catch up, eventually resulting in much smaller differences in SMC between the two fertilizer treatments.
Consistent with the lower soil moisture under 100 than 0% fertilizer in the present study, McKell et al. (1959) stated that fertilized plants reduced SMC compared to non-fertilized plants. Tesfahunegn (2019) concluded that the decrease in SMC with increased fertilizer rates was associated with increased crop water demand associated with higher crop yield. Ritchie and Johnson (1990) stated that fertilization stimulates plant growth and thus more soil water use. Other reports have also shown that additional nutrient supply can increase water and nutrient uptake by plants from the soil and produce better crop growth (Salvagiotti et al., 2008;Setiyono et al., 2010). Previous research has also shown that long-term N and P fertilization considerably increase crop water use for transpiration, resulting in decreased SMC (Caviglia & Sadras, 2001;Huang et al., 2003;Zhang et al., 2006;. The implication is that when fertilizer rate increases, there is higher soil water depletion by the plants due to more nutrients available regardless of the type of crop or variety (Caviglia & Sadras, 2001;Huang et al., 2003;Zhang et al., 2006;Zou et al. 2012;. Soil moisture depletion by both crops in 2013 started earlier under 100 than 0% fertilizer at all the soil depths, except for reseeded barley at 5 cm depth (Figures 1 and 2). Similarly in 2014, an earlier start of soil moisture depletion was noticed with 100 than 0% at all the soil depths for both crops, except canola at the 5 cm depth (Figures 3 and 4). The 2013 and 2014 results showed that more vigorous root growth with fertilizer application resulted in earlier soil moisture use. Gill (2021) observed greater length, surface area, and volume of canola and barley roots with 100% than 0% fertilizer during the early growing season of 2015 under both the minimum tillage and direct seeding systems.
Unlike the 2013 and 2014 results, the 2015 data did not show a fertilizer effect on the start of soil moisture depletion time (Figures 5 and 6). As a result of lower spring soil moisture and less rain in June 2015, relative to 2013 and 2014, soil moisture was depleted from drier soil irrespective of the fertilizer rate (Table 1).
In the study where the soil moisture data were collected, the canopy of both canola and barley usually had lighter colour and delayed development in the 0% compared to 100% fertilizer rate treatments in all years, as shown by using pictures of canola canopy in 2015 (Picture 1, Gill, 2019). Canola plant height also showed significant increase from fertilizer application, while the increase in barley height was not significant (Table 7, Gill, 2019). Even with limited soil moisture in the early growing season of 2015, early season root growth of barley and canola was better under 100 than 0% fertilizer (Gill, 2021). Compared to 0% fertilizer, canola seed yield increase with 100% fertilizer was 2.31 (162%), 2.16 (116%), and 3.02 (202%) Mg ha -1 during the 2013, 2014, and 2015 seasons, respectively (Gill, 2019). Corresponding increase for the barley seed yield was 0.96 (21%), 0.77 (15%), 0.61 (25%) Mg ha -1 . These results clearly show that same or only somewhat more water extraction with 100 compared to 0% fertilizer resulted in large seed yield increases for both crops. On a loam soil from 1967 to 1984 years, Campbell et al. (1998) reported higher wheat yield per unit of water use from better-fertilized rotations. Srivastava et al. (2020) stated that water use efficiency for corn grain yield was higher for both rainfed (N60-N100) and irrigated (N75-N125) in comparison with N0 nitrogen level. Oberle and Keeney (1990) observed that for rainfed environments, preplant and early season precipitation amounts were important factors in explaining yield responses and were the factors that caused optimal N rates for maximum corn yield; and N management could cause variation in yield with no differences in amounts of water use. Hatfield et al. (2001) stated that modifying nutrient management practices can increase WUE by 15 to 25%. Results from these studies implies that growth of both plants and roots is improved from early growth period and more seed yield is produced per unit of water used by crops when fertilized relative to no fertilizer. Further, improved water use efficiency of crops with fertilizer application can reduce the carbon footprint per unit of seed production and reduce the environment impact of crop production.
By the end of the growing season, both canola and barley tended to deplete soil moisture to a lower level under 100 than 0% fertilizer, with some exceptions. Thus somewhat less residual SMC may be expected after crops that receive 100 compared to the 0% fertilizer rate. Srivastava et al. (2020) observed cumulative evapotranspiration to be higher for both rainfed (N60-N100) and irrigated maize (N75-N125) in comparison with N0 nitrogen level. Shahadha et al. (2021) found with increasing N rate under high rainfall amounts, the crop transpiration increased whereas the soil evaporation decreased. However, soil water dynamics and crop evapotranspiration were not affected by N application rates under low rainfall amount. Less soil moisture in fertilized crops during the crop growth periods and after harvests may have positive and negative aspects. Positively, more depletion of soil moisture means more rain infiltration, with less water runoff and soil erosion in years with adequate rain. Negatively, if the root zone soil is not fully charged before the start of the next crop, the subsequent crop can suffer from water stress in dry areas.
After rapid depletion of soil moisture during their early and middle periods, crops' slower or no soil moisture depletion could be due to the reduced ability of plants to extract soil water from relatively drier soil. At lower SMC levels, the remaining water is held more tightly by soil particles (higher matric suction), or the crops being near maturity were using less water. Lower SMC at later crop growth stages suggested a lack of available SM for optimum crop growth that probably limited crop yields, especially during the 2014 and 2015 seasons.
Less SM depletion from deeper than from shallower soil depths during the early crop growth period was considered to be the result of evaporation from the surface soil plus initial shallow rooting depth (Figures 1-6). Increased SM depletion from the deeper soil during the later part of the growing seasons indicated greater root growth in the deeper soil and less water available at shallower depths. Earlier reports have shown that the root systems of crops can increase or relocate maximal root growth to regions with more water in the soil profile, thereby maintaining plant growth under dry conditions (Rendig & Taylor, 1989). Moroke et al. (2005) observed that the root length densities of sorghum (Sorghum bicolor) and sunflower (Halianthus annus) near the soil surface increased rapidly initially and then declined, while they increased throughout the growing season in the deeper soil: and depletion of soil water from the different soil depths corresponded to the root length density. During a dry year, the root length density at shallow soil depths tended to decrease during mid-season but continued to increase throughout the growing season at deeper soil depths (Moroke et al., 2005). Fan et al. (2016) stated that soil water depletion by crops depends not only on the total root system but also on the depth-wise distribution of roots. These statements support our result of more soil moisture depletion from deeper soil depths as the season progressed.
Overall, more soil moisture depletion under 100 than 0% fertilizer during considerable parts of crop growing seasons indicated an improved ability of crops to extract soil water under 100% fertilizer. The smaller differences in SMC near the end of crop growing season under both fertilizer levels indicate that if more soil moisture was available, the differences might have continued for more extended periods. The implication is that yields of the fertilized crops may have benefitted more than the unfertilized crops from additional moisture.

Conclusions
Soil moisture at the monitored depths was depleted by canola and barley crops during 2013, 2014, and 2015. The data indicated a relatively lower soil moisture level under 100% when compared to 0% fertilizer during most parts of the growing seasons. This demonstrated an improved ability of fertilized plants to extract soil water. There was generally an early start to soil water depletion when fertilizer was added. With some exceptions for the 5 and 15 cm depths, both crops could deplete soil moisture to a somewhat lower level under 100 than 0% fertilizer by the end of the growing season. Soil moisture availability probably limited crop production, especially during the 2014 and 2015 seasons. Under the area's dryland agriculture conditions, fertilizer application could alter the soil moisture depletion pattern during the growing season and somewhat reduce residual soil moisture at crop harvest. Fertilizer application also improved the water use efficiency by crops. In jas.ccsenet.org Journal of Agricultural Science Vol. 14, No. 3;2022 summary, these findings indicated that fertilizer application might reduce soil moisture availability for subsequent crops, mainly when moisture is limiting during the next growing season, but fertilizer use is recommended due to improved plant and root growth, seed yield and water use efficiency.