Effect of partial root zone irrigation and fertilizing management on grain yield and water productivity of faba bean

Water is essential for the production of biomass and grain by plants. In recent years, deficit irrigation induced by partial root zone irrigation has been one of the methods used to increase water productivity in agronomic systems. In this method, only a portion of the root system is irrigated and is exposed to semi- moistened and semi dried conditions. In sustainable agriculture , on the other hand, efforts are made to reduce the use of chemical fertilizers due to their negative impact on agronomic systems, such as reducing water and plant root penetration into soil and causing soil degradation. However, plants should be supplied with nutrients through other means, such as manure and compost. In order to reduce water consumption in agricultural systems, low-intensity irrigation has always been regarded as an essential management strategy. Due to the fact that, in the majority of the country, a decrease in precipitation occurs during the reproductive growth period of crops, resulting in a limitation of grain filling, research on limited irrigation techniques that can optimally reduce water consumption in agricultural systems is a top priority.

The research was carried out in Shadegan, Khuzestan during 2018-19. A two-factor factorial experiment based on randomized complete block design and three replications were employed to compare the treatments. The first factor was the irrigation regime applied after seedling establishment. The twoirrigation treatments were total root zone irrigation (I1) and partial root zone irrigation (I2). In complete irrigation, furrows were completely irrigated. In the partial root zone irrigation method, alternate furrow irrigation was used. The control (no fertilizer), chemical fertilizer, animal manure (cow manure), and compost comprised the second factor. Urea (100 kg ha-1), triple super phosphate (100 kg ha-1) and potassium sulfate (100 kg ha-1) were used as chemical fertilizers (50 kg ha-1). Before planting, the entire amount of compost (30 t ha-1) and cow manure (30 t ha-1) was applied. Each plot's incoming water volume was measured.

The interaction between irrigation and fertilizer had a significant effect on grain number per plant, biological yield, and water productivity (P≤0.01) and grain yield (P≤0.05). With the application of chemical fertilizer and thorough irrigation, the highest grain yield (3051 kg ha-1) was achieved. Grain yield of faba bean under partial root zone irrigation and chemical fertilizer was 9.2% more than that of complete irrigation and control (no fertilizer) treatment. The application of fertilizer increased the grain yield of faba bean under partial root zone irrigation (in chemical fertilizer, animal manure and compost was 42%, 40% and 31% more than that of control (no fertilizer), respectively). However, only when chemical fertilizer was used was the grain yield of faba bean greater under partial root zone irrigation than under full irrigation and no fertilization. Other fertilizer treatments were unable to compensate for deficit irrigation's negative effects on faba bean grain yield. The highest (1.73) and lowest (0.83) of water productivity (kg grain m-3) were achieved with the application of chemical fertilizer under partial root zone irrigation and no fertilizer application under full irrigation regime, respectively. Compost did not improved water productivity under full irrigation. However, under partial root zone irrigation, compost resulted in higher water productivity compared with all fertilizer treatments under full irrigation. The highest water productivity under partial root zone irrigation (1.73) was more than 40% more than the highest water productivity under full irrigation (1.037).

The results of the present research confirm that partial root zone irrigation can help improve water productivity by reducing water consumption while maintaining grain yield. Furthermore, animal manure and compost cannot be used as a replacement of chemical fertilizers because slow release of nutrients.