|
Establishing the Nutrient Requirements of Crops using a Systematic Approach
By T. Nagendra Rao
The soil resource base is continuously under pressure as food, fodder and fiber demands are ever increasing, while per capita availability of cultivated land is reducing. Reported annual loss of nutrients (NPK) from Indian soils is fairly large (5.4 to 8.4 mt/ha) and increasing incidence of multiple nutrient deficiencies is a growing concern (Figure 1). Thus, soils are continuously subject to change and site-specific fertility problems are occuring quite often. Under these circumstances, regular monitoring of soil fertility is a real challenge that demands rapid, reliable and less expensive techniques.
Figure 1. Food production in India vs emergence of multiple nutrient deficiencies in Indian soils
(Note: Red letters in the bars denote citation of nutrient deficiencies)
A modified procedure of the Systematic Approach (SA) outlined by Portch and Hunter (2002) was adopted to facilitates simultaneous evaluation of all essential mineral nutrients under rapidly changing soil fertility environments. The system includes soil nutrient analyses in the laboratory followed by simple green house experiments. The main idea is that before conducting any field experiment, it is always important to determine nutrient imbalances through laboratory and greenhouse experiments to prevent nutrient deficiencies from impacting on crop growth and yields. Because the analytical methods are inexpensive, repeated greenhouse experiments can be carried out in cases where there is a need for further refinement. Finally, this knowledge is then taken to field experiments to confirm and quantify nutrient requirements of field crops.
PPI/PPIC has initiated research programs in South India and Sri Lanka in collaboration with State Agricultural Universities. The Systematic Approach procedures were adopted to quickly diagnose multiple nutrient imbalances in soils and optimize the nutrient requirements of a variety of crops grown under field situations. Two case studies are presented here showing results of experiments conducted on two different soil series viz., Kalathur and Palaviduthi where rice and sugarcane were field tested.
Results:
I. Experiments on Kalathur Series (Typic Haplusterts), Tamil Nadu:
Greenhouse experiments carried out on a Kalathur series of Tamil Nadu have indicated that among the nutrients evaluated, N,P,K and Zn are the ones limiting crop growth. The relative yields of sorghum as an indicator crop were 61, 66, 75 and 75%, respectively, compared to the optimum treatment, when these nutrients are missing (Figure 2). Field experiments on rice established that application of 170, 55, 42 and 6.5 kg/ha N-P2O5-K2O-Zn has given yields close to 7 t/ha ((Murugappan and Malarvizhi, 2001). Skipping any of these nutrients from optimum dose drastically impacted the crop yields (Figure 3).
Figure 2. Relative Yields obtained with various nutrients under green house experiments
Figure 3. Response of rice to nutrient application under field experiments
II. Experiments on Palaviduthi Series (Typic Haptulastalfs), Tamil Nadu:
Experiments have established that N, P, K, Fe and Zn are the most limiting nutrients. Skipping of these nutrients from optimum has resulted in lower relative yields of up to 62, 66, 78, 80 and 84% of optimum, respectively (Figure 4). Using this information and conducting field experiments on sugarcane has established that all those five nutrients are needed to obtain good cane yields. A nutrient combination of 310,160,250,72 and 31 kg/ha N-P2O5-K2O-Fe-Zn was considered optimum and it has produced cane yields of up to 126 t/ha (Figure 5). Skipping any of those nutrients from the optimum dose has reduced the yields (Balaji, 2005).
Figure 4. Relative yields obtained in green house experiments using sorghum as indicator plant
Figure 5. Sugarcane yields with optimum nutrient doses vsmissing nutrients in field experiments
Conclusion:
It has been observed that rapidly changing soil fertility, and related nutrient imbalances, are the prime causes of declining crop productivity. There is no short cut to improve crop yields without replenishing deficient nutrients, correcting imbalances in the soils and improving soil fertility. Thus, soil fertility evaluation must become a continuous process. Developing an inventory of soil fertility information at the soil series level through the use of the Systematic Approach procedures is quite useful. The experimental results have indicated that the Systematic Approach evaluation is important for appropriately assessing the soil fertility problems. Information obtained from laboratory and greenhouse studies have predicted nutrient requirements of crops. This is ultimately confirmed through field studies.
Sources:
Balaji, T. (2005) Evaluation of Balanced Fertilization for Maximizing the Yield and Quality of Sugarcane in Theni District. Ph.D. Thesis, Dept. of Soils and Environment, Agril. College & Res. Inst., TNAU, Madurai.
Murugappan, V. and Malarvizhi, P. (2001) Systematic Approach for Evolving fertilizer Optima in Rice Based Cropping Systems. Final Report, PPIC supported research project, Tamil Nadu Agricultural University, Coimbatore.
Sam Portch and Hunter, A. (2002) A Systematic Approach to Soil Fertility Evaluation and Improvement, Modern Agriculture and Fertilizers, Spl. Publication No. 5, PPI/PPIC China Program. (To order this publication, contact Dr. T. N. Rao, Deputy Director, PPI/PPIC-India Programe. E-mail: tnrao@ppi-ppic.org)
|