Interactive Effects of Intraspecific Competition and Drought on Stomatal Conductance and Hormone Concentrations in Different Tomato Genotypes

Plant physiological responses to various stresses are characterized by interaction and coupling, while the intrinsic mechanism remains unclear. The effects of intraspecific competition on plant growth, stomatal opening, and hormone concentrations were investigated with three tomato genotypes (WT-wild type, Ailsa Craig; FL-a abscisic acid (ABA) deficient mutant, flacca; NR-a partially ethylene-insensitive genotype) under two water regimes (full irrigation, irrigation amount = daily transpiration; deficit irrigation, 60% of irrigation amount in full irrigation) in this study. Three kinds of competitions were designed, i.e., root and canopy competition, non-root competition, and non-canopy competition, respectively. Intraspecific competition reduced plant leaf area and stomatal conductance (gs) of wild-type tomato, accompanied by ABA accumulation and ethylene evolution. Intraspecific competition-induced decrease in gs was absent in FL and NR, indicating ABA and ethylene involved in plant response to intraspecific competition. As soil water becomes dry, the competition decreased gs by elevating ABA and ethylene accumulations. Under severe drought, the competition-induced decline in gs was covered by the severe drought-induced decrease in gs, as hydraulic signals most probably dominate. The absence of canopy competition insignificantly influenced plant stomatal opening of well-watered tomato, as canopy separation minimized the plant neighbor sensing by ethylene and other signals. Whereas under water deficit condition, the absence of canopy competition significantly reduced ABA accumulation in roots and then stomatal conductance, indicating the belowground neighbor detection signals maybe enhanced by soil drought. The absence of root competition increased ethylene evolution, confirming the importance of ethylene in neighbor detection and plant response to environmental stress.

Determination of Irrigation Time Using Plant Water Stress Index Values of Second Crop Sunflower in Semi-Arid Climate Conditions

This study was carried out in 2020 to determine crop water stress index (CWSI) by using infrared thermometer (IRT) data calculated by leaf canopy temperature measurements of the second crop sunflower genotype in semi-arid climate conditions, and to determine the relationships between irrigation time, seed yield of sunflower plant and CWSI by using these index values. Irrigation program consisted of a full irrigation and 2 different levels of stress, which were 100% (I100), 70% (I70), 35% (I35) of water losses within the effective root depth of 90 cm every 7 days. A total of 644 mm of irrigation water was applied to I100 (control) irrigation. The water consumption for full irrigation was 721 mm and the yield was 3516.00 kg/ha. Lower limit (LL) value without water stress required to determine plant water stress index was Tc-Ta=-2.528×VPD +0.749 (R2=0.814) and upper limit (UL) value, where the plant is completely under water stress, was determined as +3.27℃. Crop water stress index value threshold at which sunflower seed yield started to decrease was calculated as 0.33 using the infrared thermometer measurements at the time of irrigation. In addition, a negative correlation was obtained between sunflower seed yield and CWSI values. The results revealed that the yield tends to decrease as the CWSI increases.

Effect of Water Irrigation Amounts and Nitrogen Fertilizer Levels on Teosinte Productivity and Optimal Economic N-Rates Under Salinity Stress

The teosinte plant is one of the most important fodder crops that is affected by drought and nitrogen supply, and therefore the optimal supply of N- fertilization may be affected by the amount of irrigation water added to teosinte plants to obtain an economic crop. Two field experiments were done to study the effect of irrigation amount at three levels (100%, 80% and 120%) and nitrogen fertilizer levels (60, 90 and 120 kg N fed-1) (Feddan = 4200 m2) on the yield productivity of teosinte and determined the optimal and economic optimal N rate as affected by irrigation amount levels, and water relations. The results showed that the highest values of the fresh and dry weight of cuts, as well as plant height and stem diameter, were obtained when applying the full irrigation rate with full irrigation and 120 kg N fed-1. The results also showed that a 20% decrease in the irrigation rate led to a deterioration in the values of those parameters. Although the results showed that the full irrigation amount more saved water at two seasons under various levels of nitrogen. Moreover, all water relationships gave the best mean values for actual evapotranspiration, water utilization and use efficiencies also, higher application efficiency values at full irrigation and 120 kg N-levels than the other treatments. Also, the results showed that the economical yield of teosinte fresh cuts when using 211.01 kg N fed-1 with 120% of the recommended irrigation rate was higher when using 148.22 kg N fed-1 with the recommended irrigation rate. Therefore, we recommend using 211.01 kg N fed-1 to get an optimum economic yield of teosinte fresh cuts, especially in saline soil, with 120% of the recommended irrigation rate.

Optimization of Irrigation Water Depth under Water Limiting Condition

Water productivity is a major challenge in all agricultural regions and despite the use of pressurized irrigation system, it has not increased as expected in Iran. In addition, in spite of water shortage in Iran, gardeners because of lack of knowledge in economic consequences do not welcome deficit irrigation and irrigation scheduling. To this end, optimization of irrigation water depth in an orange orchard was conducted for two irrigation scheduling methods (with and without 4 days irrigation frequency) under water and land limitations conditions by mathematical analysis of production and cost functions. Then, their effect on the net income by changing in water and fruit price was assessed. Production and cost functions were developed based on two scenarios of applied water including only irrigation water depth and irrigation water depth plus rainfall. According to results, when water is limiting, by using the optimum water depth (Ww), 26% of irrigation water use can be saved that causes only 3–4% decrease in the net income per unit of land and 16% increase in the net income per unit of irrigation water. In addition, when water limiting is serious, using 46% deficit irrigation (Wew) is more useful and resultes the highest water productivity, even though it causes 14–17% decrease in the net income per unit of land. However in water limiting condition, if land is not limiting, using Wew causes the maximum net income per unit of land even 50–60% more than full irrigation. Moreover, using the optimum water depths in water limitation conditions (Ww and Wew) increases the water productivity 26–47% relative to full irrigation. On the other side, the net income and the amount of optimum water depths are not sensitive to the price of water at the present value of water. However, they are highly sensitive to the price of fruit. Furthermore, having an irrigation schedule causes 27% increase in the net income per unit of land. According to positive effects of deficit irrigation and irrigation scheduling on the water productivity and the income, they are highly recommended for addressing water scarcity in Iran.

Response of Pear Trees’ (Pyrus bretschneideri ‘Sinkiangensis’) Fine Roots to a Soil Water Regime of Regulated Deficit Irrigation

A field experiment was conducted to evaluate the effects of regulated deficit irrigation (RDI) on the fine root redistribution of mature pear trees in 2009 and 2010. The experiment consisted of four RDI treatments: MRDI-1 and SRDI-1, in which the trees received irrigation replacing 60% and 40% of pan evaporation (Ep) during Stage 1 (cell division stage), and MRDI-1+2 and SRDI-1+2, in which the trees received irrigation replacing 60% and 40% of Ep during Stage 1+2 (cell division and slow shoot growth stage). All the RDI-treated trees received irrigation replacing 80% of Ep (full irrigation) in other stages, and the control trees were fully irrigated during the whole growth season. The results showed that the fine root length density (RLD) of mature pear trees was reduced by water stress. The resumption of full irrigation boosted fine root growth. The RLD of the SRDI-1-treated trees in the irrigated zones recovered in early July, they maintained water and nutrient absorption during the fruit enlargement stage, and the final fruit yield was significantly improved. The RLD of trees in the irrigated zones with MRDI-1 and MRDI-1+2 recovered in July and September, respectively, but there were no significant differences in fruit yield between the MRDI-1, MRDI-1+2, and the control. This indicates that the fruit yield was not negatively or positively impacted by the redistribution of moderate water stress applied during either Stage 1 or Stage 1+2.

Impact of drought stress on biochemical responses, energy, and water productivity on maize forage (Zea mays L.)

Drought stress is the most important limiting factor in crop plants including maize (Zea mays L.), which is the third important world crop after wheat and rice. To examine the quantity and quality of forage as well as energy and water productivity of two maize varieties to drought stress, a field experiment was carried out as a split plot based on a completely randomized block design with three replications in Isfahan, Iran, during 2017 and 2018 growing seasons. The main and sub-plots were three irrigation regimes (100%, 80, and 60% full irrigation) and two maize varieties (704 and Maxima), respectively. Data analysis showed that drought stress harmed wet and dry forage yield and energy productivity, while its effect was positive on some forage quality such as ash, neutral detergent fiber (NDF), hemicellulose free cell wall (ADF), and lignin (ADL). Based on results, drought stress of 60% full irrigation resulted in reduced wet and dry forage maize yields. In addition, drought stress affected relationships among measured traits. According to increasing dried fodder and decreasing output energy under stress conditions, early mature variety Maxima is more proper to be used under drought stress. Besides, the Maxima variety was shown to be a suitable variety due to increasing dry matter and crude protein as well as decrease ADF and ADL than the 704 variety. Article Highlights We submit an original research article entitled Effect of water stress on forage yield and quality and water and energy productivity in Maize (Zea mays L.). In this paper, we indicated regarding to impacts of climate change phenomenon throughout the world on crop production, especially in arid regions such as Iran, choosing proper variety can be one of the best candidates to provide for forage. The results of present paper have shown that the drought stress had no effect on water productivity of two maize varieties. The superiority of some forage quality traits in drought stress compared to the control in maize means that in drought conditions, maize forage can be used and increase the profitability of livestock products.

Peanut yield under irrigation levels in off-season cultivation

Water deficit is considered the most critical environmental factor for peanut production in Brazil, as it constitutes one of the major constraints to the expansion of its cultivation in the suitable crop zones of the country. Determining crop water demand is fundamental to increasing yield with lower water consumption. The present study aimed to evaluate the effects of full and deficit irrigation levels (L1 = 8%, L2 = 27%, L3 = 63%, L4 = 94% and L5 = 100% replenishment of crop evapotranspiration) on the development, growth and yield of peanut crop sown in two times, February and March. Treatments were distributed in a split-plot randomized complete block design, with four replicates, using a line-source sprinkler system. Irrigation depths from 65 to 314 mm were applied with the levels L1 to L5 during the first and second cropping cycles. Full irrigation with sowing in March was more advantageous due to yield increase of up to 30% compared to sowing in February, but crop cycle was 25 days longer. Water stress caused by deficit irrigation reduced plant height, seed mass and pod yield, while full irrigation (L5) led to yields from 4,141 to 5,102 kg ha-1 for February and March, approximately three times higher than those obtained with the lowest irrigation level (L1). Highlights Peanut has great importance in the food and industry of several countries. The results of this research apply to regions that require irrigation, which is of about 70% of the areas of the globe with this legume. This paper contributes with information that emphasizes the possibility of cultivation in the drought season, aiming at the expansion of the crop and the production of quality seeds using irrigation.

Effect of Phosphorus Application Methods on Growth and Yield of Maize under Water Deficit Conditions

A field study was conducted to investigate effect of phosphorus and different levels of irrigation on growth and yield of maize at the Agronomic Research Area, Faculty of Agricultural sciences and Technology, Bahauddin Zakariya University, Multan, during autumn 2016.The Experiment was laid out in randomized complete block design (RCBD) with split plot courses of action having three replications with net plot size of 4m x 3m. The crop was sown in 75 cm spaced rows, while plant to plant distance was maintained at 30 cm with the help of dibbler. Experimental treatments comprised of two irrigation level sand four phosphorus levels. The crop was harvested at maturity and the data were recorded by using the standard procedures. Maximum grain yield was obtained at full irrigation levels where phosphorus was applied @ 100 kg ha-1. All the growth and yield parameter increased with full irrigation levels with application of Phosphorus at the rate of 100 kg ha-1 while it was decreased where half irrigation was applied. Increase in P2O5 rates upto100 kg ha-1 enhanced the plant height, cob length, cob weight, thousands grain weight, Beyond application of 100 kg P2O5 ha-1 there was no significant increase in number of grains cob-1, thousand grain weight and other growth parameters. It is recommended that maize crop should preferably be fertilized @ 100 kg Phosphorus per hectare to get maximum grain yield under the ecological conditions of Multan.