1. AGSC 231 Principles of Agronomy Fertilization - I By S.K. Yau, revised April 2010

2. Content Nitrogen The main factors affecting crop response to N

3. General Introduction adequate level of soil fertility foremost requisite to economic crop production if not adequate, need to add as fertilizers or manure any practice other than fertilizer application that improves crop yield speeds up depletion of soil mineral elements

4. N deficient?

5. What deficiency?N deficiency

6. N deficient plantsN sufficient plants

7. Nitrogen - introduction What symptoms and consequences if deficient? pale yellow, and poor growth & quality

8. Strip of plants suffers from N deficiency

9. Nitrogen - introduction What symptoms and consequences if deficient? pale yellow, and poor growth & quality What will happen if adequate? healthy green, rapid stem & leaf development and growth

10. Double rate of N fertilizer

11. Any effects if N oversupplied? No toxicity effect Tends to cause lodging, poor seed development, and/or greater disease susceptibility in some crops

12. What are the main factors affecting crop response to N? 1.The soil type - N fertilizers cause a grain yield increase in crops in almost all soils, except for peat and muck soils (high in organic matter & N).

13. What are the main factors affecting crop response to N? (cont.) 2.The moisture regime under which a crop is grown has a dominant influence. In high rainfall or irrigated conditions, the optimal N rate is usually higher than in dry areas. Or in other words, N fertilization may not increase seed yield in rain-fed arid lands.

14. Response of dry matter yield to N application

15. Response of seed yield to N application affected by irrigation

16. Schematic graph showing generalized seed yield response to levels of fertilization in relation to soil moisture supply

17. Bonus Q: Why no response to N in rainfed dry areas? Not enough precipitation to dissolve the N fertilizers. Right or wrong?

18. Why in rain-fed arid lands, crops may not respond to N application? In Mediterranean areas, precipitation comes only in late fall, winter, and early spring.

19. Why in rain-fed arid lands, crops may not respond to N application? In Mediterranean areas, precipitation comes only in late fall, winter, and early spring. Crops use the stored soil moisture to grow rapidly in spring and produce seed before the hot dry summer. Excessive N application may cause excessive growth early in the season, depleting soil moisture before grain is produced.

20. What are the main factors affecting crop response to N? Crop species – some crops may not response to N application if N available deeper down in the soil profile and these crops have deep roots. Example: safflower.

21. Under rain-fed conditions

23. Please study the book on How to maintain N fertility in soil? Are there non-symbiotic N fixation? What are the common N fertilizers?

24. Summary Soil types, moisture regime, and crop species are the main factors affecting the response to N. In rain-fed, arid Mediterranean areas, crops may not respond to N application because N may cause excessive growth early in the season depleting soil moisture before grain is produced.

25. 2nd bonus Q AT AREC, what yield increase will you expect if you apply 100 kg N/ha to 1. a non-irrigated field which usually gives 1000 kg barley/ha without N application? 2. to a field with supplementary irrigation which usually gives 3000 kg barley/ha without N application?