تاثیر محدودیت آبیاری بر عملکرد و کیفیت علوفه گندم و شبدر ایرانی در کشت مخلوط

یک پژوهش مزرعه‌ای در سال زراعی 95-1394 در شهرستان سلسله اجرا گردید تا اثر آبیاری محدود ناشی از آبیاری جزئی ریشه بر عملکرد و کیفیت علوفه و بهره‌وری آب گندم و شبدر ایرانی در کشت خالص و مخلوط مورد بررسی قرار گیرد. آزمایش به صورت فاکتوریل دو عاملی بر پایه طرح بلوک‌های کامل تصادفی با سه تکرار انجام شد. عامل اول روش آبیاری (آبیاری کامل و آبیاری جزئی سیستم ریشه‌ای) و عامل دوم الگوی کاشت (کشت خالص گندم، کشت خالص شبدرایرانی، کشت مخلوط روی ردیف‌های جداگانه و کشت مخلوط روی یک ردیف) بود. نتایج نشان داد که عملکرد علوفه در تمامی الگوهای کاشت به طور منفی تحت تاثیر آبیاری جزئی ریشه قرار گرفت. با اعمال آبیاری جزئی ریشه، تولید ماده خشک در کشت خالص گندم، کشت خالص شبدر ایرانی، کشت مخلوط روی یک ردیف و کشت مخلوط روی ردیف‌های جداگانه به ترتیب 16، 15، 9 و 8 درصد کاهش پیدا کرد. آبیاری جزئی ریشه باعث بهبود بهروه‌وری آب برای تولید علوفه در کلیه الگوهای کاشت شد. کشت‌های مخلوط دارای بیشترین درصد افزایش بهره‌وری آب (برای کشت مخلوط روی یک ردیف و روی ردیف‌های جداگانه به ترتیب 83 و 77 درصد) بودند. آبیاری جزئی ریشه کیفیت علوفه در کشت مخلوط را کاهش داد به طوری که adf و ndf به ترتیب 6 و 4 درصد افزایش و پروتئین خام و ماده خشک قابل هضم به ترتیب 15 و 7 درصد کاهش پیدا کردند. با این حال، کیفیت علوفه در کشت مخلوط بیشتر از کشت خالص گندم بود. نسبت برابری زمین تنها در شرایط آبیاری جزئی ریشه بیشتر از یک بدست آمد (1.024) که 8.8 درصد بیشتر از مقدار آن در شرایط آبیاری کامل ریشه بود. به عبارت دیگر برای تولید علوفه، کشت مخلوط گندم و شبدرایرانی تنها در شرایط آبیاری جزئی ریشه دارای مزیت است.

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

IntroductionOne 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 semiarid 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 rootzone 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 rootzone irrigation, where a large amount of water saving and low yield reduction is occurred by partial rootzone irrigation. The aim of this experiment was to investigate the quantity and quality of forage produced in intercropped wheat and Persian clover under partial rootzone irrigation condition.Materials and methodsThe experiment was conducted as a field experiment during 201617 growing season in Lorestan province. A twofactor 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, withinrow intercropping and betweenrow 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 rootzone irrigation. Dry matter production of sole wheat, sole Persian clover, withinrow intercropping and alternaterow intercropping was reduced 16%, 15%, 9% and 8% by partial rootzone 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 irrigationThe quality of forage produced in intercropping reduced by partial rootzone irrigation method. Digestible dry matter (DDM) of wheatPersian clover intercropping reduced by 7% with applying partial rootzone irrigation. Partial rootzone irrigation reduced crude protein content of sole Persian clover, withinrow intercropping and alternaterow intercropping by 15%, 14% and 16%, respectively. ADF and NDF of forage produced in withinrow and alternaterow intercropping of wheat and Persian clover was increased 6% and 7% by applying partial rootzone 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 alternaterow intercropping of wheat and Persian clover. The highest (104.19 kg mm1 ha1 dry matter) and lowest (43.5 kg mm1 ha1 dry matter) water use efficiency for forage production was achieved in sole wheat under partial rootzone irrigation and sole Persian clover under conventional irrigation, respectively. Partial rootzone irrigation improved water use efficiency of all planting patterns for forage production. Withinrow intercropping of wheat and Persian clover had highest (84.94 kg. mm1. ha1) water use efficiency for digestible dry matter under partial rootzone irrigation method which was 3 times more than that of conventional irrigation. Persian clover with partial rootzone irrigation produced highest crude protein (kg ha1) 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 rootzone 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 partialroot 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 rootzone irrigation, resulting in the reduction of forage qualityConclusionCompared to conventional irrigation, partial rootzone 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 rootzone 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.