كليدواژه :
بهينه‌سازي مصرف نيتروژن , شاخص تغذيه نيتروژني , كمبود نيتروژن , كمبود نيتروژن , مدل‌سازي , مديريت دقيق نيتروژن
چكيده فارسي :
بهبود رشد گياه زراعي با كاربرد كود نيتروژن مي‌تواند به‌ميزان قابل توجهي عملكرد محصول را افزايش و بازده اقتصادي را بهبود بخشد. با اين‌حال، استفاده بيش از حد از كود نيتروژن در نظام‌هاي كشت فشرده منجر به كاهش كارايي زراعي مصرف نيتروژن، افزايش انتشار گاز‌هاي گلخانه‌اي و آلودگي آب و خاك شده است. غلظت نيتروژن بحراني (Nc) حداقل نيتروژن مورد نياز براي حداكثر رشد گياه است و مي‌تواند به‌عنوان ابزاري براي مديريت دقيق نيتروژن در طي فصل رشد استفاده شود. مطالعه فعلي با هدف تعيين منحني رقيق شدن غلظت نيتروژن بحراني بر مبناي ماده خشك برگ (LDM) در كلزاي بهاره (Brassica napus L.) انجام شد. براي اين منظور، يك آزمايش مزرعه‌اي با هفت سطح مصرف صفر، 50، 100، 150، 200، 250 و 300 كيلوگرم نيتروژن خالص در هكتار انجام گرفت و ماده خشك و غلظت نيتروژن برگ دو رقم كلزاي بهاره در طي فصل رشد اندازه‌گيري شد. منحني رقيق شدن غلظت نيتروژن بحراني برگ كلزاي بهاره با رابطه Nc=5.08LDM-0.06 توصيف شد. شاخص تغذيه نيتروژني (NNI) بسته به‌ميزان مصرف نيتروژن در رقم دلگان از 0/72 تا 1/14 و در رقم هايولا 401 از 0/53 تا 1/15 متغير بود. كمبود نيتروژن تجمعي (Nand) در رقم دلگان بين 11/61- و 107/09 كيلوگرم نيتروژن در هكتار و در رقم هايولا 401 بين 24/22- و 129/64 كيلوگرم نيتروژن در هكتار تعيين شد. همبستگي مثبت معني‌داري بين اختلاف ميزان مصرف نيتروژن (ΔN) با تغييرات شاخص تغذيه نيتروژني (ΔNNI) و كمبود نيتروژن تجمعي (ΔNand) وجود داشت. به‌طور كلي، منحني رقيق شدن غلظت نيتروژن بحراني و شاخص تغذيه نيتروژني و كمبود نيتروژن تجمعي مشتق از آن به‌خوبي وضعيت محدوديت و عدم محدوديت تغذيه نيتروژني را در دو رقم كلزاي بهاره مشخص كرد و مي‌تواند به‌عنوان شاخص قابل‌اطميناني از وضعيت نيتروژن گياه زراعي در طي فصل رشد استفاده شود.
چكيده لاتين :
Introduction
Supplementing crop growth with nitrogen (N) can significantly increase yields. However, the excessive use of N in
intensive cropping systems has led to lower N use efficiency, an increase in greenhouse gas emissions as well as
water pollution. The critical N concentration (Nc) is the minimum N required for maximal growth and can be used as
a tool for accurate N management during the growing season. Leaf dry matter (LDM) is an important indicator of
crop growth potential and a measure of light-energy utilization, and yield formation in rapeseed. LDM increases as
more N fertilizer is applied, although differences in LDM are small under high fertilization levels. Therefore,
construction of a N
c curve based on LDM during the vegetative growth of spring rapeseed would be a worthwhile
objective. Our aims in the present study were (i) to construct a leaf Nc curve, (ii) to compare this curve with
published data, and (iii) to explore its potential for estimating spring rapeseed leaf N status.
Materials and Methods
A field experiment with seven levels of N fertilizer including 0, 50, 100, 150, 200, 250 and 300 kg.ha-1 was
performed, and LDM and leaf N concentration (LNC) of two spring rapeseed cultivars were measured during the
growing season. The procedure used for constructing the leaf Nc curve was first proposed by Justes et al. (1994).
The N nutrition index (NNI) on each sampling date was calculated by dividing LNC by leaf Nc concentration. The
accumulated N deficit (Nand) in leaves for each sampling date was determined by subtracting the N accumulation in
leaves under the N
c condition from actual N accumulation in leaves under different N rates.
Results and Discussion
N application rate exhibited a significant effect on LDM during the vegetative growth of rapeseed. The LDM
increased gradually with increasing N utilization. LDM ranged from 0.06-3.83 ton.ha-1 for Hyola 401 cv. and from
0.06-3.56 ton.ha-1 for Dalgan cv. LNC generally increased with increasing N application. LNC remained relatively
stable during the early growth but decreased gradually as cultivars reached the flowering stage. LNC values ranged
from 2.44-6.2% for Hyola 401 cv. and from 3.14-6.1% for Dalgan cv. The leaf Nc concentrations in Hyola 401 and
Dalgan cultivars declined with increasing LDM and the curve for these cultivars was fitted according to the equation
N
c=5.08LDM-0.06. The similar trends of decline in leaf N dilution have been previously reported in winter wheat,
maize and rice, when N dilution was estimated on the whole plant or specific plant organs basis. NNI values began
to decrease with the decrease in the quantity of applied N. NNI values varied from 0.72-1.14 in the Dalgan cv. and
from 0.53-1.15 in the Hyola 401 cv. The NNI values were greater than one for non-N limiting treatments and less
than one for N-limiting treatments. These results confirm that NNI can provide accurate and quantitative insight into
the N nutrition status of rapeseed. The Nand values ranged between -11.61-107.09 kg N ha-1 in the Dalgan cv. and
between -24.22-129.64 for the Hyola 401 cv. depending on the N dosage. Nand decreased with increased N rates,
while intensified gradually over growth progress of rapeseed and reached its peak at flowering stage for N-limiting
treatments. These results confirmed the usefulness of Nand for assessing N nutrition in spring rapeseed. There was a
significant positive correlation between the changes in N application rates (ΔN) and the changes in NNI (ΔNNI),
and between ΔN and the changes in Nand (ΔNand). Generally, the Nc dilution curve, NNI, and Nand derived from it
well recognized nutrition status of two cultivars under N-limiting and non-N limiting conditions, and can be used to
as a reliable indicator of the crop N status during the growing season. Conclusion
The N concentration in the canopy leaves decreased with advancing maturity, while a higher N application rate
generally exhibited a higher leaf N concentration. The present Nc dilution curve based on LDM provides an insight
into N nutrition status in spring rapeseed plant and can serve as a novel tool to improve N fertilization management
in rapeseed.
