Comparison of Rice N Uptake in Paddies with Different Organic Carbon

Abstract

Efficient use of all inputs is vital to achieve and sustain high crop

yields, maintain resource quality and minimize environmental pollution.

Fertilizer N is one of the major inputs in rice production. Blanket fertilizer

recommendations do not take into account the high field-to-field variability

and within-season dynamic changes in indigenous N supply.

Since the plant growth reflects the total N supply from all sources, plant

N status will be a good indicator of N availability to crops at any given

time. Leaf colour chart (LCC) is simple portable diagnostic tool, to

determine the timing of N top dressing. We used it to test need-based

N-management approaches for rice (Oryza sativa L.) and compared

LCC with split three rates (45, 90 and 135) and three timing at two

sites, in northern Iran. Grain yield, yield attributes, total N uptake and

fertilizer-N use efficiency were measured. All treatments showed significant

grain yield increase relative to zero-N control. Yield loss was

observed when split 135 timing was used in both sites due to lodging

and pest damage. Grain yield of LCC treatments were higher than split

treatments. The grain yield of zero-N control in site 2 was 18.5 % higher

than that of site 1 due to higher soil organic matter percent. LCC 5

treatment had higher AE than LCC 4 and fixed - 135 at the less N rate.

As a result LCC treatments indicated that N management based on LCC

shade 5 helped avoid over application of N to rice.