Forage yield and quality of intercropped wheat and Persian clover as affected by partial root zone irrigation

Introduction One of the most common ways to increase the quality of cereal forage is to mix them with legume family plants. Growing of crop mixtures with legumes, which is named intercropping, can amplify the forage quality of livestock diet. The main obstacle for agriculture in arid and semi-arid areas is the limitation of available water resources. Thus, the management of limited water for irrigation is crucial. Several patterns have been introduced for saving water in agricultural systems. Partial root-zone irrigation is a method which has been considered in recent years for saving water. In this irrigation method, half of root system is irrigated and other half is exposed to dry soil, so that the irrigation water amount is much lower than that of conventional irrigation. Increasing water use efficiency is one of the most important benefits of partial root-zone irrigation, where a large amount of water saving and low yield reduction is occurred by partial root-zone irrigation. The aim of this experiment was to investigate the quantity and quality of forage produced in intercropped wheat and Persian clover under partial root-zone irrigation condition. Materials and methods The experiment was conducted as a field experiment during 2016-17 growing season in Lorestan province. A two-factor factorial experiment based on randomized complete block design with three replications was employed to compare the treatments. The fist factor was irrigation (conventional irrigation (I1) and partial root zone irrigation (I2)) which was applied after seedling establishment. The second factor was planting pattern including sole wheat, sole Persian clover, within-row intercropping and between-row intercropping. Water consumption was measured during growing period. At harvest time, forage yield and quality (in terms of CP, DDM, CF, NDF, and ADF) were determined. Water use efficiency was measured for forage yield and. Land equivalent ratio was used to evaluate the advantage of intercropping. Results and discussion The forage yield of all planting patterns was negatively affected by partial root-zone irrigation. Dry matter production of sole wheat, sole Persian clover, within-row intercropping and alternate-row intercropping was reduced 16%, 15%, 9% and 8% by partial root-zone irrigation, respectively. LER was more than one (1.024) only under partial root zone irrigation which was 8.8% more than that of conventional irrigation. In other word, for forage production, intercropping of wheat and Persian clover has advantage only under partial root zone irrigation The quality of forage produced in intercropping reduced by partial root-zone irrigation method. Digestible dry matter (DDM) of wheat-Persian clover intercropping reduced by 7% with applying partial root-zone irrigation. Partial root-zone irrigation reduced crude protein content of sole Persian clover, within-row intercropping and alternate-row intercropping by 15%, 14% and 16%, respectively. ADF and NDF of forage produced in within-row and alternate-row intercropping of wheat and Persian clover was increased 6% and 7% by applying partial root-zone irrigation, respectively. Persian clover had the highest WSC. The lowest WSC was achieved in sole cropping of wheat. However, Persian clover had the lowest crude fiber (CF) which was not significantly difference with alternate-row intercropping of wheat and Persian clover. The highest (104.19 kg mm-1 ha-1 dry matter) and lowest (43.5 kg mm-1 ha-1 dry matter) water use efficiency for forage production was achieved in sole wheat under partial root-zone irrigation and sole Persian clover under conventional irrigation, respectively. Partial root-zone irrigation improved water use efficiency of all planting patterns for forage production. Within-row intercropping of wheat and Persian clover had highest (84.94 kg. mm-1. ha-1) water use efficiency for digestible dry matter under partial root-zone irrigation method which was 3 times more than that of conventional irrigation. Persian clover with partial root-zone irrigation produced highest crude protein (kg ha-1) for the consumption of each unit of water. Except sole wheat, water use efficiency (for crude protein production) of other planting pattern improved about 50% with partial root-zone irrigation. Positive effects of wheat shading on Persian clover helped Persian clover to maintain its leaf water content, showing that Persian clover was less affected by partial-root zone irrigation in intercropping and was able to produce more dry matter, resulting in higher DM of intercropping. Increasing ADF and ADF of sole and intercropped forage showed that more fiber was accumulated in plants with partial root-zone irrigation, resulting in the reduction of forage quality Conclusion Compared to conventional irrigation, partial root-zone decreased forage production of sole and intercropping patterns. However, water consumption of wheat and Persian clover significantly decreased in all cropping stands, resulting in the increase of water use efficiency on the basis of forage quantity and quality. As a final remark, our experiment has confirmed the hypothesis that partial root-zone irrigation could be a good irrigation management of wheat and Persian clover intercropping for forage production in areas with a sever limitation in irrigation water supply.