California Crop Fertilization Guidelines

Soil nitrate samples should be taken about 10 days before a planned application ^[N19]. Nitrate is easily leached below the root zone with excess irrigation water, so the test may overestimate available N if a heavy irrigation or rainfall occurs.

Rooting depth for all dry bean types can exceed 4 feet; however, most nutrient uptake is from the top two feet ^{[N19,N25,N30]}. Soil samples for nitrate analysis should therefore be taken to a depth of two feet. The California bean production manual recommends sampling in increments of 0-6", 6-12" and 12-24", to get an idea of the proportion of soil N that is likely to be leached below the plant root zone ^[N20,N21].

Due to the variability of N in the soil, care must be taken that the sample is representative for the field. Unusual areas should be sampled separately ^[N20,N21]. See Sampling for Soil Nitrate Determination for instructions on sampling methods.

Residual soil nitrate is directly available to plants. The nitrate present in the rooting zone can therefore be subtracted from the crop N requirements to determine the amount of fertilizer N that needs to be applied, provided the nitrate is not leached below the root zone with early-season irrigation. Every ppm of residual nitrate N in one foot of soil is equivalent to 3-4 lbs N/acre. That is, an average test value of 10 ppm N in the top two feet of soil would mean that 60-80 lbs N/acre may be subtracted from the total N rate. See In-season N: Rate for more details.

Irrigation water may contribute a significant amount of N ^[N20]. Well water samples should be taken after the pump has been run for several hours, to make sure that the water sampled is representative of what the field will receive.

Nitrate-N contained in well water can be calculated as the ppm of nitrate-N x 2.72 = lbs N applied in one acre foot of water. For example, a test value of 7 ppm nitrate-N in a field receiving 2 acre-feet of water per year would mean that 38 lbs N/acre are added annually with the irrigation water.

If the concentration of nitrate rather than nitrate-N is given, multiply by 0.614 rather than 2.72 ^[N3]. More information about calculating the fertilizer N value of irrigation water can be found here.

All beans form symbiotic associations with Rhizobium bacteria, which are able to fix N from the atmosphere into a form the plant can use. Depending on the bean variety and environmental conditions, this process may supply only part of the plant's N requirement. Inoculating seeds with Rhizobia may be beneficial, when the type of bean has not been grown in the field for a while. Different types of beans form relationships with different Rhizobium strains, so care should be taken to inoculate with the correct strain.

Common beans (Phaseolus vulgaris) only need to be inoculated if they have not been grown in the field for more than 10 years ^[N2,N21]. Blackeye beans (actually a cowpea, Vigna unguiculata) should be inoculated if they have not been grown in the field before. While it has not been determined if further inoculation is necessary, it is commonly practiced ^[N14].

It's recommended to inoculate lima beans (Phaseolus lunatus) and garbanzos (Cicer arietinum) each time they are planted, unless they are in very short rotations ^[N20,N23].

Fungicides and insecticides used to treat bean seeds often kill Rhizobium cultures. Using a granular inoculum, rather than a powder or peat-based form, placed in the seed row at planting, can prevent damage to the bacteria by the fungicide ^[N20,N23].

Soil and weather conditions affect how much N the bacteria are able to fix. N fixation is highest in well-drained, neutral pH soils with good organic matter content ^[N2]. In acid soils, wet soils and under hot and dry weather conditions, N fixation may be reduced and a greater proportion of the plant's N needs will have to be supplied by fertilizer or the soil. If soil nitrate levels are high, N fixation from the atmosphere will often be reduced, and less benefit will be gained from Rhizobium inoculation ^[N2].

Several studies on irrigated garbanzos in the Central Valley have showed yield responses to broadcast and incorporated pre- plant N fertilizer ^{[N27,N28,N29]}. One study carried out at the West Side Field Station found that a pre- plant N application of 80 lbs N/acre as urea increased garbanzo yields by about 240 lbs/acre compared with a no-N control. Doubling the application rate had no effect on yield, which reached 2,700 lbs/acre ^[N29]. Another study at the same location observed that increasing the application rate from 80 to 160 lbs N/acre increased yield by 260 lbs/acre, from 4,170 lbs/acre to 4,430 lbs/acre ^[N27]. However, the entire rate in these studies was broadcast and incorporated pre-plant, suggesting that smaller rates could be appropriate if the fertilizer was banded and most of the rate sidedressed.

For lima beans, a small starter application of 8 lbs N/acre banded at planting is recommended ^[N20]. If a 8-24-6 fertilizer is used, this rate corresponds to 100 lbs/acre dry material or 10 gallons/acre of liquid fertilizer. Double this amount is suggested for common bean, which has a short season and high N requirement during vegetative growth ^[N13,N21].

California experiments with blackeyes on research stations and in farmer fields suggest that N applied pre-plant or at sowing does not usually increase yields ^[N1,N10]. However, a small amount of banded starter N can stimulate the growth of young plants, allowing them to compete better with weeds ^[N1,N10]. This benefit is likely stronger for varieties with more compact growth habits.

If beans are planted into recently incorporated small grain or corn residues, additional N may be needed to compensate for soil N tied up in residue decomposition. As a rule of thumb, 15 lbs N/acre may be applied for each ton of residue, up to 3 tons ^[N2,N7].

Starter N is normally banded with P. Bands should be placed at least 2 inches to the side and 2 inches below the seed. Fertilizer should never be placed directly in contact with the seed ^[N21]. If bands contain more than 20 lbs N/acre, seeds may be injured ^[N7]. Higher rates may be placed further away, or broadcast over the beds pre-plant and incorporated ^[N27]. However, broadcasting is probably not the most efficient strategy.

Germinating bean seeds are susceptible to salt damage and ammonium toxicity, particularly limas and common beans. Therefore, urea-based fertilizers and diammonium phosphate (DAP; 18-46-0 or 16-48-0) should be avoided, especially on dry or sandy soils. A low-N, high-P fertilizer such as monoammonium phosphate (MAP; dry 11-52-0 or liquid 10-34-0) is preferred for lima beans ^[N20]. For many bean crops, 8-24-6 is used in starter applications (Roland Meyer, personal communication).

Fact sheets of the most common fertilizers can be found on the web site of the IPNI.

Starter fertilizers are normally applied at planting. Large applications may be incorporated or injected prior to planting. However, applying a large proportion of the N requirement pre-plant is inefficient, especially for beans planted during the winter months.

Dry bean N requirements depend on the yield, the total amount of N taken up by the plant, and the amount of N the plant is able to fix from the atmosphere (See Table).

When calculating in-season application rates, the N applied pre-plant or as starter needs to be subtracted from the N requirement, as well as the nitrate present in the soil and irrigation water. See Soil Test N for more information.

Estimated N budgets for dry bean crops with a yield goal of 2500 lbs/acre. Adapted from ^{[N9,N11,N20,N21,N26]}.

The table assumes N-fixation rates ranging from of 20-40%, 20-60% and 20-50% for common, garbanzo and lima beans, respectively. A rate of 90% is assumed for blackeyes ^[N11]. Assumes garbanzo N harvest index of 0.7-0.85, which is based on studies from Australia and Saskatchewan ^[N9,N12].

Since tissue N concentration and N fixation are strongly influenced by variety, soil and weather, the ranges in the table are approximate. The proportion of N fixed from the atmosphere will be on the low end of the range in dry, hot weather or when the soil is waterlogged. High fertilizer application rates may also reduce N fixation. This makes yield maximization through fertilization an expensive strategy ^[N10].

As a general guideline, the UC bean production manuals suggest a sidedress application of 100 lbs N/acre for lima bean (yield goal 2500- 3000 lbs N/acre) and 70-100 lbs N/acre for common bean (yield goal 2000 lbs N/acre), adjusted for other nitrate sources ^[N20,N21]. This is in line with the findings of Cahn and coworkers ^[N4], who found bean yield was maximized with about 75 lbs N/acre banded near the seed at sidedressing, across all tested varieties and planting dates. Yields in this study ranged between 1600-2400 lbs/acre.

Sidedress N is normally injected in a band during cultivation ^[N21]. For most bean crops, it's suggested to shank fertilizer in 8 to 10 inches deep and at least 10-15 inches away from the bean row, to avoid pruning the roots ^[N20]. If sprinkler or subsurface drip irrigation is used, N fertilizer may also be fertigated through the irrigation water.

The source of N does not appear to affect bean performance ^[N2]. Aqua ammonia or a similar N fertilizer is commonly used for sidedressing ^[N21]. Fact sheets of the most common fertilizers can be found on the web site of the IPNI.

Sidedressing is normally done during cultivation at layby, prior to row closure and before bloom. It should not be done too late, as cultivation can seriously damage roots of established plants, and may increase disease potential ^[N1,N21].

Soil samples can be taken at any time between crops, as soil P and K change less rapidly than nitrate. However, samples should be taken at the same time each year. Rooting depth for all dry bean types can exceed 4 feet ^{[P11,P17,P21]}; however, since P and K are not very mobile in most soils, pre-plant soil samples for P and K may be taken to a depth of 6 inches ^[P12]. Parts of a field which perform differently or are differently managed should be sampled separately ^[P12]. See Soil Test Sampling for sampling instructions.

The Olsen-P test works well in soils with pH 6.5 and above, and is the test normally most appropriate in California. The Bray-1 test should be used for soils with pH below 6.5.

Critical soil levels of P and K for selected California dry bean types. Adapted from ^[P6,P12,P13].

The University of California has not published a critical soil P threshold for garbanzos. Guidelines for garbanzo production in the Palouse region of the Pacific Northwest suggest that P applications are beneficial up to an Olsen P test value of 14 ppm ^[P3]. However, a trial in Fresno County on a soil which had a pre-plant Olsen P of 7 ppm did not find any yield or quality response to P fertilizer rates ranging from 50-200 lbs P₂O₅/acre ^[P18].

Appropriate P rates are based on yield expectations and soil test P (see Table). When soil test P is intermediate, beans may be fertilized based on removal with the harvest. Beans contain about 0.4-0.5% P, meaning that for each 2000 lbs of harvested beans, 18- 23 lbs P₂O₅ (8-10 lbs P) are removed ^[P2,P10,P19]. The rates given below assume that P will be banded; if it is broadcast, rates may be doubled ^[P4].

Suggested P fertilizer application rates to lima beans based on soil test P in the top 6 inches of soil ^[P12].

Rates for common bean are similar, although when soil test P is very low, slightly higher rates may be needed to achieve a high yield goal ^[P13].

In California, blackeyes are unlikely to respond to P fertilizer if soil test P is greater than 5 ppm. An application of 100 lbs P₂O₅/acre is recommended if soil test P approaches or is below 5 ppm. This will build up soil P for several years ^[P6].

While irrigated garbanzos have been shown to respond to P applications elsewhere ^[P8], experiments to determine appropriate P rates in California have not been conclusive. An experiment on a low-P soil at the West Side Research station in Fresno County did not see any yield or quality response to P additions ranging from 50-200 lbs P/acre ^[P18]. The yields in this study averaged 4,000 lbs/acre.

Phosphorus may be held strongly on soil surfaces, especially in acidic or calcareous soils. Applying P fertilizer in concentrated bands allows the fertilizer to exceed the soil's fixation capacity and increases P availability. This is especially important early in the season, when the root system is small but a good P supply is important. Bands should be placed at least 2 inches to the side and 2 inches below the seed. Fertilizer should never be placed directly in contact with the seed, especially if it also contains N or K ^[P3,P13].

Broadcasting P is less efficient than banding. If P is broadcast higher rates should be used. Broadcast P needs to be incorporated to a depth of 4-6 inches, since P is not mobile in the soil and surface broadcast P will not be available to bean roots ^[P3].

Germinating bean seeds are susceptible to salt damage and ammonium toxicity. Therefore, urea-containing blends and diammonium phosphate should be avoided, especially in dry or sandy soils. A low-N, high-P fertilizer such as monoammonium phosphate (MAP; dry 11-52-0 or liquid 10-34-0) is preferred ^[P13].

A number of granular and liquid P fertilizers are available. Fact sheets of the most common fertilizers can be found on the web site of the IPNI.

It is important to have a good P supply during seedling development. Therefore, all P is normally applied at planting. Phosphorus is important for initiating the nodules responsible for N fixation, and although late P fertilization can help to compensate for reduced early nodulation ^[P9], a high N supply during early vegetative growth is important, especially for common bean, which has a short season ^[P5,P13].

Soil samples can be taken at any time between crops, as soil P and K change less rapidly than nitrate. However, samples should be taken at the same time each year. Rooting depth for all dry bean types can exceed 4 feet ^[K7,K15,K21]; however, since P and K are not very mobile in most soils, pre-plant soil samples for P and K may be taken to a depth of 6 inches ^[K8]. Parts of a field which perform differently or are differently managed should be sampled separately ^[K8]. See Soil Test Sampling for sampling instructions.

In California, soil available K is normally measured as ammonium-acetate extractable K ^[K8].

Critical soil levels of P and K for selected California dry bean types. Adapted from ^[K4,K8,K9].

The University of California has not published a critical soil K threshold for garbanzos.

Application rates should be based on soil test K level (see Pre-plant K).

K applications can be made based on crop removal. While K concentrations in beans vary, on average they contain about 1-2% K ^[K3,K6,K16]. This means that a 2,000 lb/acre crop would remove 24-48 lbs K₂O/acre (20-40 lbs K). This is in line with the University of California recommendation to apply about 2.5 lbs K₂O for every 100 lbs of expected yield of common bean when soil test K is very low (0-40 ppm), and about 1 lb K₂O for every 100 lbs of expected yield when it is moderate (41-80 ppm) ^[K10]. Lima beans have a somewhat lower requirement (see Table). Suggested K application rate (lbs K₂O/acre) to lima beans, based on levels of exchangeable K in the top 6 inches of soil ^[K8].

No University of California recommendations have been developed for K application to garbanzo beans or blackeyes. Average K concentrations are similar to those of common bean ^{[K13,K17,K19]}, and similar fertilizer replacement values can be assumed.

Studies with blackeyes and common bean suggest K fertilizer can help mitigate the effects of drought and salinity stress ^[K18,K20].

Potassium can be broadcast and incorporated, or banded. Since K is not very mobile in most soils, broadcast K should be incorporated to ensure good root access. Potassium fertilizer should not be placed in contact with the seed, as this can affect germination. If a heavy application is needed to correct a deficiency, it's safest to apply K before or during seedbed preparation rather than at planting ^[K11].

Many K fertilizers can be used. Salinity can damage beans' ability to germinate, so high-salt index fertilizers such as muriate of potash (potassium chloride, KCl) should be used with caution. More information on K fertilizers may be found at the IPNI website.

Potassium is normally applied at or prior to planting. When beans are grown in rotation with more demanding crops, such as cotton, K is often applied at other points in the rotation rather than before beans ^[K1].