Balanced and Integrated Nutrient Management in Soybeanbased Cropping Systems

In an era of multiple nutrient deficiencies, a single nutrient approach can lower fertilizer-use efficiency. Balanced nutrition implies that there are no deficiencies, excesses, antagonisms or negative interactions. All deficient nutrients must be at an optimum rate by themselves and in relation to each other, enabling positive interactions to enhance yields. Field trials conducted in different villages of central India on black soils deficient in nitrogen, phosphorus, sulphur and zinc have shown that balanced fertilization (BF) through the application of NPKSZn at recommended rates (25 kg N, 60 kg P2O5, 20 kg K2O, 20 kg S and 5 kg Zn ha-1) produced a higher soybean seed yield by 30-35% over farmers' usual practice (12.5 kg N and 30 kg P2O5 ha-1) (Fig. 8.1). Omitting the application of phosphorus (NKSZn treatment) and sulphur (NPKZn treatment) had resulted in a 15-19% reduction in

■ NPKSZn

H NKSZn

0 NPSZn

g NPKZn

□ NPKS

FP

H FP+S+Zn

c C3

Fig. 8.1. Effect of balanced fertilization on soybean seed yield (I indicates the LSD at P = 0.05) (reprinted with permission from Subba Rao et al., 2006).

FP, farmers' practice.

Fig. 8.1. Effect of balanced fertilization on soybean seed yield (I indicates the LSD at P = 0.05) (reprinted with permission from Subba Rao et al., 2006).

FP, farmers' practice.

soybean seed yield as compared to NPKSZn treatment. Similarly, the soybean seed yield was reduced significantly when zinc was not applied. The application of sulphur (20 kg ha-1) and zinc (5 kg ha-1) along with farmers' practice produced 19% more soybean yield over farmers' practice alone (Subba Rao et al, 2006).

The interactive advantage of the combined use of all possible sources of nutrients and their scientific management in integrated nutrient management (INM) has proved superior to the use of each component alone for optimum growth, yield and quality of different crops and cropping systems in specific agro-ecological situations. The basic concept underlying the principle of INM is to maintain or adjust plant nutrient supply to achieve a given level of crop production by optimizing the benefits from all possible sources of plant nutrients. The basic objectives of INM are to reduce the inorganic fertilizer requirement or use, restore organic matter in soil, enhance nutrient-use efficiency by synergetic interactions and maintain soil quality in terms of physical, chemical and biological properties. Bulky organic manures may not be able to supply adequate amounts of nutrients; nevertheless, their role is important in meeting the above objectives. Organic manures are known to decrease phosphorus adsorption/ fixation and enhance phosphorus availability in phosphorus-fixing soils (Reddy et al., 1999a). Organic anions formed during the decomposition of organic inputs can compete with phosphorus for the same sorption sites and thereby increase phosphorus availability in the soil (Iyamuremye et al., 1996) and improve utilization by crops. Reddy et al. (1999b) observed

Table 8.4. Apparent phosphorus recovery (APR) of fertilizer phosphorus in soybean and wheat (mean of 5 years) (reprinted with permission by Elsevier from Reddy et al., 1999b).

Rate of fertilizer phosphorus (kg P ha-1)

(t ha-1)ab APR by soybean (%) APR by wheat (%)

0 (0)

_

36.6

30.0

19.0

_

35.1

27.8

17.7

4 (5.6)

-

44.1

31.8

19.1

_

33.4

32.8

19.2

8 (11.2)

_

46.5

35.2

22.7

_

35.9

33.9

23.1

16 (22.4)

_

47.0

35.8

23.2

_

40.3

38.5

26.9

Mean

_

43.6

33.2

21.0

_

36.2

33.2

21.6

aManure with fertilizer phosphorus applied to soybean, whereas wheat received only fertilizer phosphorus.

bFigures in parentheses are phosphorus applied through manure.

aManure with fertilizer phosphorus applied to soybean, whereas wheat received only fertilizer phosphorus.

bFigures in parentheses are phosphorus applied through manure.

higher apparent phosphorus recovery by a soybean-wheat system on ver-tisol with a combination of fertilizer phosphorus and manure (Table 8.4). Organic manures play a direct role in supplying macro- and micronutri-ents and an indirect role by improving the physical, chemical and biological properties of soils. These manures, besides supplying nutrients to the current crop, very often have a substantial residual effect on succeeding crops in the system. The integrated use of chemical fertilizers and FYM has had a marked influence on improving the physical, chemical and biological quality of soil.

In the recent past, several INM strategies have been developed for soybean-based cropping systems in India and other countries. On-farm trials conducted on farmers' fields in central India have revealed that the INM module, comprising '50% NPKS + 5 t FYM ha-1 + Rhizobium to soybean and 75% NPKS + phosphate-solubilizing bacteria (PSB) to wheat' increased the soybean seed yield by 46% and the wheat grain yield by 24% over farmers' practice (Table 8.5) (Sammi Reddy et al., 2007).

Conservation tillage and double-cropping practices may alter fertilizer nitrogen requirements due to a lowered soil nitrogen supply. Hairston et al. (1987), working on an Okolona silty clay soil in Mississippi, found that 25 lb N acre-1 (28 kg N ha-1) increased soybean yield only when planted no-till into wheat stubble and demonstrated a lack of benefit when straw was removed, burned or incorporated. In addition, net returns were increased the most in response to nitrogen fertilization for the no-till treatment. In central India, wheat residue incorporation/surface retention with or without FYM/poultry manure resulted in higher crop yields and led to an improvement in organic carbon and nutrient availability of soil under a soybean-wheat system as compared to residue burning. The value to cost

Table 8.5. Economics of integrated nutrient management (INM) in soybean (average of years 2005 and 2006) (reprinted with permission from Sammi Reddy et al., 2007).

Mean grain

Gross

Details of the nutrient

yield

income

Total costa

Net returns

management option

(kg ha-1)

(Rs ha-1)

(Rs ha-1)

(Rs ha-1)

VCR

100% NPKSZn to soybean and

1,953

21,483

10,919

10,564

0.97

100% NPKS to wheat (BF)

50% NPKS + 5 t FYM ha-1 to

2,051

22,561

10,520

12,041

1.14

soybean and 75% NPKS to

wheat (INM 1)

50% NPKS + 5 t FYM ha-1 +

2,182

24,002

10,545

13,457

1.28

Rhizobium to soybean and 75%

NPKS + PSB to wheat (INM 2)

Farmers' practice

1,727

18,997

9,693

9,304

0.96

BF, balanced fertilization through inorganic fertilizers only; PSB, phosphate-solubilizing bacteria; VCR, value to cost ratio.

100% NPKSZn: soybean - 25 kg N, 60 kg P2O5, 20 kg K2O, 20 kg S and 5 kg Zn ha-1; wheat - 120 kg N, 60 kg P2O5, 20 kg K2O and 20 kg S.

Farmers' practice: soybean - 12.5 kg N and 30 kg P2O5 ha-1; wheat - 80 kg N and 50 kg P2O5 ha-1. aTotal cost includes the cost of fertilizers, manure and all other costs of cultivation.

BF, balanced fertilization through inorganic fertilizers only; PSB, phosphate-solubilizing bacteria; VCR, value to cost ratio.

100% NPKSZn: soybean - 25 kg N, 60 kg P2O5, 20 kg K2O, 20 kg S and 5 kg Zn ha-1; wheat - 120 kg N, 60 kg P2O5, 20 kg K2O and 20 kg S.

Farmers' practice: soybean - 12.5 kg N and 30 kg P2O5 ha-1; wheat - 80 kg N and 50 kg P2O5 ha-1. aTotal cost includes the cost of fertilizers, manure and all other costs of cultivation.

ratio (VCR) was 14.7 for residue incorporation and 3.1 for residue retention (Reddy, 2007a).

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